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Title: The Waste Products of Agriculture
Author: Albert Howard
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THE WASTE PRODUCTS OF AGRICULTURE (1931)
Their Utilization as Humus
BY ALBERT HOWARD, C.I.E., M.A.
Director of the Institute Of Plant Industry, Indore,
and Agricultural Adviser to States in Central India and Rajputana
AND
YESHWANT D. WAD, M. Sc.
Chief Assistant in Chemistry, Institute of Plant Industry, Indore
To
SIR REGINALD GLANCY
K.C.I.E., C.S.I., C.I.E., I.C.S.
Member of the Council of India
Formerly Agent to the Governor-General in Central India
First President of the Board of Governors of the Institute of Plant
Industry, Indore (1924-1929)
PREFACE
One of the main features of crop production at the present day is waste.
Except in the Far East, where the large indigenous population has to be
fed from the produce of the country-side, little is being done to
utilize completely the by-products of the farm in maintaining the
fertility of the soil. The ever-growing supplies of agricultural
produce, needed by industry and trade, have been provided either by
taking up new land or by the purchase of artificial manures. Both these
methods are uneconomic. The exploitation of virgin soil is a form of
plunder. Any expenditure on fertilizers which can be avoided raises the
cost of production, and therefore reduces the margin of profit. It needs
no argument to urge that, in maintaining the fertility of the soil, the
most careful attention should be paid to the utilization of the waste
products of agriculture itself before any demands are made on
capital--natural or acquired.
For the last twenty-six years, the senior author has been engaged in the
study of crop production in India and in devising means by which the
produce of the soil could be increased by methods within the resources
of the small holder. These investigations fell into two divisions: (1)
the improvement of the variety; and (2) the intensive cultivation of the
new types. In the work of replacing the indigenous crops of India by
higher yielding varieties, it was soon realized that the full
possibilities in plant breeding could only be achieved when the soil in
which the improved types are grown is provided with an adequate supply
of organic matter in the right condition. Improved varieties by
themselves could be relied on to give an increased yield in the
neighbourhood of ten per cent. Improved varieties plus better soil
conditions were found to produce an increment up to a hundred per cent
or even more.
Steps were therefore taken: (1) to study the conversion of all forms of
vegetable and animal wastes into organic matter (humus) suitable for the
needs of the growing crop; and (2) to work out a simple process by which
the Indian cultivator could prepare an adequate supply of this material
from the by-products of his holding. In other words he has been shown
how to become a chemical manufacturer. This task involved a careful
study of the various systems of agriculture which so far have been
evolved and particularly of the methods by which they replenish the soil
organic matter. The line of advance in raising crop production in India
to a much higher level then became clear. Very marked progress could be
made by welding the various fragments of this subject--the care of the
manure heap, green-manuring and the preparation of artificial farmyard
manure--into a single process, which could be worked continuously
throughout the year and which could be relied upon to yield a supply of
humus, uniform in chemical composition and ready for incorporation into
the soil. This has been accomplished at the Institute of Plant Industry
at Indore. The work is now being taken up in Sind and at various centres
in Central India and Rajputana.
The Indore process for the manufacture of humus is described in detail
in the following pages. It can be adopted as it stands throughout the
tropics and sub-tropics, and also on the small holdings and allotments
of the temperate zone. How rapidly the method can be incorporated into
the large-scale agriculture of the west is a question which experience
alone can answer. It will in all probability depend on how far the
process can be mechanized.
In the field of rural hygiene there is great scope for the new method.
It can be applied to the utilization of all human, animal and vegetable
wastes in such a manner that the breeding of flies is prevented, the
water and the food-supply of the people safeguarded and the general
health of the locality improved. Cleaner and healthier villages will
then go hand in hand with heavier crops.
A.H.
Y.D.W.
Indore
6 April, 1931
CONTENTS
I INTRODUCTION
II ORGANIC MATTER AND SOIL FERTILITY
III THE SOURCES OF ORGANIC MATTER
IV THE MANUFACTURE OF COMPOST BY THE INDORE METHOD
V THE CHIEF FACTORS IN THE INDORE PROCESS
VI APPLICATION TO OTHER AREAS
APPENDIXES:--
A The Manurial Problem in India
B Some Aspects of Soil Improvement in Relation to Crop Production
C Nitrogen Transformation in the Decomposition of Natural Organic
Materials at Different Stages of Growth
D An Experiment in the Management of Indian Labour
Of composts shall the Muse disdain to sing?
Nor soil her heavenly plumes? The sacred Muse
Nought sordid deems, but what is base nought fair,
Unless true Virtue stamp it with her seal.
Then, planter, wouldst thou double thine estate,
Never, ah! never, be asham'd to tread
Thy dung-heaps. (From Grainger's The Sugar Cane.)
INTRODUCTION
The maintenance of the fertility of the soil is the first condition of
any permanent system of agriculture. In the ordinary processes of crop
production, fertility is steadily lost; its continuous restoration by
means of manuring and soil management is therefore imperative.
In considering how the ideal method of manuring and of soil management
can be devised, the first step is to bring under review the various
systems of agriculture which so far have been evolved. These fall for
the most part into two main groups: (1) the methods of the Occident to
which a large amount of scientific attention has been devoted during the
last fifty years; and (2) the practices of the Orient which have been
almost unaffected by western science.
The systems of agriculture of the Occident and of the Orient will now be
briefly considered with a view of extracting from each ideas and results
which can be utilized in the evolution of the ideal method of
maintaining and increasing the fertility of the soil.
NOTE: In the general organization of agriculture, Europe stands mid-way
between the east and the west and provides, as it were, the connecting
link between these two methods of farming.
THE AGRICULTURAL SYSTEMS OF THE OCCIDENT
The most striking characteristic of the agriculture of the west is the
comparatively large size of the holding. Large farms are the rule; small
holdings are the exception.
NOTE: The growth of allotments for the production of vegetables in the
neighbourhood of urban areas is a comparatively recent phenomenon and
only affects a small area.
The large farms of the west are for the most part engaged in the
production of food and a few raw materials like wool for the urban
populations of the world, which are mainly concerned with manufacture
and trade. To produce these vast supplies, and at the same time to place
them on the markets at low rates, practically all the unoccupied
temperate regions of the world, which are suitable for the white races,
have already been utilized. The best areas of North America, of the
Argentine, of South Africa and large tracts of Australia and practically
the whole of New Zealand have during the last hundred years been
exploited to produce the endless procession of cargoes of food and raw
materials required by the great markets of the world.
The weakness of this system of agriculture lies in the fact that it is
new and has not yet received the support which centuries of successful
experience alone can provide. At first it was based on the exploitation
of the stores of organic matter accumulated by virgin land, which at the
best could not last for more than a limited number of years. Even now
there is practically no attempt to utilize the large quantities of wheat
straw and other vegetable wastes for keeping up the store of organic
matter in the soil. The new areas of North America for example soon
showed signs of exhaustion. Manuring has become necessary as in the case
of the older fields of Europe. To supply the large quantities of
combined nitrogen needed, all possible sources except the right one--the
systematic conversion of the waste products of agriculture into
humus--have one after the other been utilized: guano from the islands
off the Peruvian coast, nitrate of soda from Chile, sulphate of ammonia
from coal and more recently synthetic nitrogen compounds obtained from
the atmosphere. These substances are supplemented by another class of
nitrogenous organic manures such as artificial guanos, dried blood and
slaughter-house residues, oil cakes and wool waste--the by-products of
agriculture--and by another group of artificials--the various phosphatic
and potassic fertilizers. These supplies of concentrated manures have
enabled agricultural production to be kept at a high level. The fact of
their existence for a time tended to distract attention from the fullest
utilization of the by-products of the farm. Recently, however, a change
has taken place and a large amount of scientific effort has been devoted
to the problems which centre round the waste products, both animal and
vegetable, of agriculture itself. The need of keeping up the supply of
organic matter in the soil is now widely recognized.
After the large size of the holding and the necessity of manuring, the
high cost of labour is another leading characteristic of western
farming. The number of men per square mile of agricultural land who
actually work is low.
NOTE: The comparative figures of crop production per worker for the
five-year period preceding the War, prepared by the United States
Department of Agriculture, are instructive. The number of workers
employed per 1,000 acres of crop land was approximately 235 in Italy,
160 in Germany, 120 in France, 105 in England and Wales, 60 in Scotland
but only 41 in the United States. In Canada, according to Riddell, the
1911 figures show that every 1,000 acres called for only 26 workers.
This observer states that in the three prairie provinces (Alberta,
Manitoba, Saskatchewan) the figures are even more striking: the area
under field crops was 17,677,091 acres, and the numbers engaged in
agriculture was 283,472, so that each person so employed was responsible
for 62 acres. Every 1,000 acres required only 16 workers. Since these
data were published, further statements have appeared from which it
would seem that the size of the working population in agriculture in
North America has shrunk still further.
This state of things has arisen from the dearness and scarcity of
labour, which has naturally led to the study of labour-saving devices
including the use of machinery. Whenever a machine can be invented which
saves human labour its spread is rapid. Engines of various kinds are the
rule everywhere. The inevitable march of the combine-harvester, in all
the wheat-producing areas of the world, is the latest example of the
mechanization of the agriculture of the west. Another feature of this
extensive system of large-scale agriculture is the development of food
preservation processes, of transport and of marketing, by which the
products of agriculture are cheaply and rapidly moved from the field to
the centres of distribution and consumption. There is no great dearth of
capital at any stage. Money can always be found for any new machine and
for any new development which is likely to return a dividend. Land and
capital are abundant; efficient transport and good markets abound. The
comparatively small supply of suitable labour and its high cost provide
the chief agricultural problems of the west.
This system of agriculture is essentially modern and has developed
largely as one of the consequences of the discovery of the steam engine
and the rapid exploitation of the supplies of coal, oil and water-power.
It has only been made possible by the existence of vast areas of virgin
land in parts of the earth's surface on which the white races can live
and work. As already mentioned the weak point in this method of crop
production is that it is new and lacks the backing which only a long
period of practical experience can supply. Mother Earth is provided with
an abundant store of reserve fertility which can always be exploited for
a time. Every really successful system of agriculture however must be
based on the long view, otherwise the day of reckoning is certain.
Side by side with this method of utilizing the land there has been a
great development of science. Efforts have been made to enlist the help
of a number of separate sciences in studying the problems of agriculture
and in increasing the production of the soil. This has entailed the
foundation of numerous experiment stations, which every year pour out a
large volume of printed results and advice to the farmer. At first the
scientific workers naturally devoted themselves to solving local
problems and to furnishing scientific explanations of various
agricultural practices. This phase is now passing. A new note is
beginning to appear in the publications of the experiment stations,
namely that of direction and advice which can only be advanced by men
whose education and training combine the ideas of science with the aims
of the statesman. The feeling is not only growing but is being expressed
that it is no longer the business of science merely to solve the
problems of the moment. Something more is needed. The chief function of
science in the agriculture of the future is to provide intelligent
direction in general policy and to point the way.
THE AGRICULTURAL SYSTEMS OF THE ORIENT
Peasant Holdings
The chief feature of the agricultural systems of the east is the small
size of the holding. The relation between man-power and cultivated area
in India is given in Table I. In this table, based on the Census Report
of 1921, the number of workers and the acreage cultivated have been
calculated for the chief provinces of British India. Incidentally these
figures illustrate how intense is the struggle for existence in this
portion of the tropics.
TABLE I.--THE RELATION BETWEEN MAN-POWER AND CULTIVATED AREA IN INDIA
Provinces Number of acres cultivated by 100 ordinary cultivators
Bombay 1,215
North-West Frontier Province 1,122
Punjab 918
Central Provinces 848
Burma 565
Madras 491
Bengal 312
Bihar and Orissa 309
Assam 296
United Provinces 251
These minute holdings are frequently cultivated by extensive methods
(those suitable for large areas) which neither utilize the full energies
of man and beast nor the potential fertility of the soil. Such a system
of agriculture can only result in poverty. The obvious line of advance
is the gradual introduction of more intensive methods, for which the
supply of suitable manure, within the means of the average cultivator,
is bound to prove an important factor.
If we turn to the Far East, to China and Japan, a similar system of
small holdings is accompanied by an even more intense pressure of
population both human and bovine. In the introduction to Farmers of
Forty Centuries, King states that the three main islands of Japan had in
1907 a population of 46,977,003, maintained on 20,000 square miles of
cultivated fields. This is at the rate of 2,349 to the square mile or
more than three people to each acre. Note that these figures agree very
closely with those quoted in the Japan Year Book of 1931 in which the
number of persons per square kilometre is given as 969: equivalent to
2,433 to the square mile.
In addition Japan fed on each square mile of cultivation a very large
animal population--69 horses and 56 cattle, nearly all employed in
labour; 825 poultry; 13 swine, goats and sheep. Although no accurate
statistics are available in China, the examples quoted by King reveal a
condition of affairs not unlike Japan. In the Shantung Province, a
farmer with a family of twelve kept one donkey, one cow and two pigs on
2.5 acres of cultivated land--a density of population at the rate of
3,072 people, 256 donkeys, 256 cattle and 512 pigs per square mile. The
average of seven Chinese holdings visited gave a maintenance capacity of
1,783 people, 212 cattle or donkeys and 399 pigs--nearly 2,000 consumers
and 400 rough food transformers per square mile of farm land. In
comparison with these remarkable figures, the corresponding statistics
for 1900 in the case of the United States per square mile were:
population 61, horses and mules 30.
The problems of tropical agriculture for the most part relate to small
holdings. The main purpose of this peasant agriculture is crop
production; animal husbandry is much less important. In India the crops
grown fall into two classes--(1) food and fodder crops and (2) money
crops. The former includes, in order of area: rice, millets, wheat,
pulses and fodder crops, barley and maize and sugar-cane. The money
crops are more varied; cotton and oil seeds are the most important,
followed by jute and other fibres, tobacco, tea, opium, indigo and
coffee. It will be seen that food and fodder crops comprise 82 per cent
of the total area under crops and that money crops, as far as extent is
concerned, are relatively unimportant.
TABLE II.--AGRICULTURAL STATISTICS OF BRITISH INDIA, 1926-27
Area, in acres, under food and fodder crops
Rice 78,502,000
Millets 38,776,000
Wheat 24,181,000
Gram 14,664,000
Pulses and other good grains 29,154,000
Fodder crops 8,940,000
Condiments, spices, fruits,
vegetables, and misc. food crops 7,537,000
Barley 6,387,000
Maize 5,555,000
Sugar 3,041,000
TOTAL, FOOD AND FODDER CROPS 216,737,000
Area, in acres, under money crops
Cotton 15,687,000
Oil seeds, chiefly rape and
mustard, sesamum, groundnuts
and linseed 14,999,000
Jute and other fibres 4,411,000
Dyes, tanning materials, drugs,
narcotics and miscellaneous crops 1,729,000
Tobacco 1,055,000
Tea 738,000
Opium 59,000
Indigo 104,000
Coffee 91,000
TOTAL, MONEY CROPS 38,873,000
The primary function of Indian agriculture is to supply the cultivator
and his cattle with food. Compared with this duty all other matters are
subsidiary. The houses are built of mud, thatched with grass and are
almost devoid of furniture. Expenditure on clothing and warmth is, on
account of the customs of the country and the nature of the climate,
much smaller than in European countries. Nevertheless, the cultivators
require a little money with which to pay the land revenue and to
purchase a few necessaries in the village markets. Hence the growth of
money crops to the extent of about one-fifth the total cultivated area.
The produce, after conversion into cash, is afterwards either worked up
in the local mills or exported. To some extent food crops are also money
crops. The population of the towns and cities is largely fed from the
produce of the soil, while in addition a small percentage of the total
food grains produced is exported to foreign countries. In some crops
like sugar-cane, the total out-turn is insufficient for the towns and
large quantities of sugar are imported from Java, Mauritius and the
continent of Europe.
When we come to the details of soil management, a further striking
difference between the methods in vogue in the west and on the peasant
holdings of the east is at once manifest. In China, fertility has for
centuries been maintained at a high level without the importation of
artificial manures. Although it was not till 1888, after a protracted
controversy lasting thirty years, that western science finally accepted
as proved the important part played by pulse crops in enriching the
soil, nevertheless centuries of experience had taught the peasants of
the east the same lesson. The leguminous crop in the rotation is
everywhere one of their old fixed practices. Moreover, on the alluvium
of the Indo-Gangetic Plain, the deep, spreading root-system of the
pigeon pea (Cajanus indicus Spreng.) is utilized by the peasantry as an
efficient substitute for the periodical subsoil ploughing which these
closely-packed, silt-like soils require. In the case of the best
cultivators, the general soil management and particularly the
conservation and utilization of combined nitrogen has already reached a
high level. This has been described, in the case of the United Provinces
of India, by Clarke in a recent paper which has been reproduced as
Appendix B. In China and Japan not only the method of soil management
but also the great attention that is paid to the systematic preparation,
outside the field, of food materials for the crop from all kinds of
vegetable and animal wastes compelled the admiration of one of the most
brilliant of the agricultural investigators of the last generation. The
results are set out by King in his unfinished work--Farmers of Forty
Centuries--which should be prescribed as a textbook in every
agricultural school and college in the world.
Another feature of this agriculture is the cultivation of rice wherever
the soil and water-supply permit. In the scientific consideration of the
methods of soil management under which the rice crop of the Orient is
produced, practical experience at first seems to contradict one of the
great principles of the agricultural science of the Occident, namely the
dependence of cereals on nitrogenous manures. Large crops of rice are
produced in many parts of India on the same land year after year without
the addition of any manure whatever. The rice fields of the country
export paddy in large quantities to the centres of population or abroad,
but there is no corresponding import of combined nitrogen.
Taking Burma as an example of an area exporting rice beyond seas, during
the twenty years ending 1924, about 25,000,000 tons of paddy have been
exported from a tract roughly 10,000,000 acres in area. As unhusked rice
contains about 1.2 per cent of nitrogen the amount of this element,
shipped overseas during twenty years or destroyed in the burning of the
husk, is in the neighbourhood of 300,000 tons. As this constant drain of
nitrogen is not made up for by the import of manure, we should expect to
find a gradual loss of fertility. Nevertheless this does not take place
either in Burma or in Bengal, where rice has been grown on the same land
year after year for centuries. Nearly the soil must obtain fresh
supplies of nitrogen from somewhere, otherwise the crop would cease to
grow. The only likely source is fixation from the atmosphere, probably
in the submerged algal film on the surface of the mud. This is one of
the problems of tropical agriculture which calls for early
investigation.
Another important difference between the east and the west concerns the
supply of labour. In the Orient it is everywhere adequate, as would
naturally follow from the great density of the rural population. Indeed
in India it is so abundant that if the time wasted by the cultivators
and their cattle for a single year could be calculated as money, at the
local rates of labour, a perfectly colossal figure would be obtained.
One of the problems underlying the development of agriculture in India
is the discovery of the best means of utilizing this constant drain, in
the shape of wasted hours, for increasing crop production. There is
therefore no lack of human labour in developing the agriculture of the
east. Another favourable factor is the existence of excellent breeds of
work-cattle and of the buffalo.
NOTE: The buffalo is the milch cow of the Orient and is capable not only
of useful labour in the cultivation of rice, but also of living and
producing large quantities of rich milk on a diet on which the best
dairy cows of Europe and America would starve. The digestive processes
of the buffalo is a subject which appears to have escaped the attention
of the investigators of animal nutrition.
The last characteristic of this ancient system of agriculture is lack of
money. Again there is a great contrast between the east and the west.
There is little or no spare capital for the improvement of the holding.
Over large tracts of India at any rate, the cultivators are in the hands
of the moneylender and indebtedness is the rule. For many years one of
the pre-occupations of Government has been the discovery of safeguards
by which the cultivator can be saved from the worst consequences of his
own folly--reckless borrowing for unproductive purposes--and maintained
on the land. The recent development of co-operation and the rapid
increase in the number of primary credit societies has only been
possible because of this volume of indebtedness.
PLANTATIONS
While small holdings, accompanied by a dense population, are an
important feature of eastern agriculture, nevertheless there are
exceptions. Throughout this portion of the tropics European enterprise
has removed the original forest and established in its place extensive
plantations of such crops as sugar-cane, tea, rubber and coffee. The
labour for these estates is obtained from indigenous sources; the
capital and management are contributed by Europeans. Plantations of this
kind are common all over the east and are an important feature of the
agriculture of Java, Ceylon, the Federated Malay States, Assam and the
uplands of Southern India. One of the features of this agriculture is
the attention paid to manurial problems. Comparatively large sums of
money are expended every year in the purchase of artificial manures,
mainly for keeping up the supply of combined nitrogen. During a tour in
Ceylon in 1908, when visits were paid by the senior author to a number
of tea estates, the managers invariably produced their manurial
programme on which suggestions were always invited. Ceylon at that time
offered a tragic example of the damage which results from uncontrolled
tropical rainfall on sloping land, from which the forest canopy had been
removed without providing a proper system of terracing combined with
surface-drainage. Over large areas of hilly country, formerly forest and
now exclusively under tea, practically the whole of the valuable surface
soil rich in humus had been lost by denudation. The tea plant was
producing crops from the relatively poor subsoil, supplemented by the
constant application of expensive manures.
In a recent review of this question in Crop Production in India
published in 1924, the damage which has resulted from erosion on the
plantations of the Orient was referred to (pp. 14-5) as follows:--
It is in the planting areas of the east, however, that the most
striking examples of soil denudation are to be found. Instances
of damage to the natural capital of the country are to be seen on
the tea estates near Darjeeling, on the hill-sides in Sikkim on the
upper terraces in the vale of Kashmir, in the Kumaon Hilis, on
the tea estates in Ceylon and Assam, and in the planting districts
of Southern India and the Federated Malay States. In most of
these areas forest land was so abundant that the need for the
preservation of the soil was not at first recognized. Thanks to the
efforts of Hope, a former scientific officer employed by the tea
industry in Assam the control of the drainage and the checking
of erosion are now widely recognized and are being dealt with by
the planters in many parts of India. A great impetus to this
work was given by the publication in India of a detailed account of
the methods in use by the Dutch planters in Java, where the
terracing and drainage of sloping land, under tea and other crops
has been carried to a high stage of perfection. In this island
the area of land available for planting is strictly limited, while
the feeding of the large indigenous population is always a
serious problem. As a consequence the development of the island is
very strictly controlled by the Government, and one of the
conditions of planting new forest lands is the provision of a
suitable system of terraces combined with surface-drainage.
The advantage is not all on the side of the State. The manuring of
tea soils in Java is far less necessary than in Ceylon and
India, while one important consequence of the retention of the
valuable soil made by the forest is healthy growth, which
suffers remarkably little damage from insect and fungoid pests.
UNDEVELOPED AREAS
Very large stretches of the Orient are still under forest and at present
carry a very small population, supported by hunting, fishing and by the
small cultivated areas surrounding the villages. These undeveloped
forest areas occur everywhere, particularly in the Malay Archipelago,
the Federated Malay States, Burma and the low country of Ceylon. In the
search for the ideal method of manuring in the tropics, the greatest
care will have to be taken to preserve the valuable surface soil
whenever the forest canopy has to be removed for the creation of new
cultivated land. Some at any rate of these potentially rich tracts are
almost certain to be taken up during the present century. They will
therefore provide ample opportunities of applying any lessons in soil
management, which science can extract from experiment and from
experience. The serious mistakes of the past must not be repeated when
the time comes for developing the vast areas of tropical forest still
untouched.
It will be evident that the systems of agriculture of the west and of
the east are very different and that the two have little or nothing in
common. In a sense these two methods of managing land remind one of the
two sides of a coin. The one supplements the other: each can be regarded
as a part of one great whole. Clearly when attempting to evolve the
ideal system of manuring and soil management of the future, both of
these widely different methods of agriculture must be studied. This has
been done by the senior author for the last twenty-six years in various
parts of India--on the alluvium of the Indo-Gangetic plain at Pusa in
Bihar, on the loess soils of the Quetta Valley on the Western Frontier
and on the black cotton soils of peninsular India at Indore. The chief
climatic factors at Indore are represented in Plate II. The climate of
Quetta resembles generally that of Persia, where the rainfall is
received mainly during the winter months, often in the form of snow. At
these three centres a method of utilizing all the vegetable and animal
wastes of the holding has gradually been evolved. The latest scientific
work of the Occident and particularly that recently accomplished at the
experiment station of New Jersey, together with the practices in vogue
in India and the Far East, have been welded together and synthesized
into a system for the continuous manufacture of manure throughout the
year so that it forms an integral part of the industry of agriculture.
In considering all this information--the various agricultural systems in
use at the present time, as well as the large volume of scientific
papers dealing with manurial questions, which have been poured out by
the experiment stations during the last fifty years, we have been
impressed by the evils inseparable from the present fragmentation of any
large agricultural problem and its attack by way of the separate
science. All this seems to follow from the excessive specialization
which is now taking place, both in the teaching and in the application
of science. In the training given to the students and in much of the
published work, the tendency of knowing more and more about less and
less is every year becoming more marked. For this reason any review of
the problem of increasing soil fertility is rendered peculiarly
difficult, not only by the vast mass of published papers but also by
their fragmentary and piecemeal nature.
No extra labour is required in our manure factory. No imported chemicals
such as Adco are needed in this process. No capital is required at any
stage of the manufacture. The methods now in use at Indore form the main
subject of this book, which also attempts to deal with a number of
related matters such as--the role of organic matter in the soil, the
methods of replenishing the supply of organic matter now in use and the
recent investigations which have been carried out on the conditions
necessary for converting raw organic residues into humus which can be
immediately nitrified in the soil and so made use of by the plant. The
Indore process can easily be carried out, not only in the tropics but
also on the small holdings of the temperate regions and on the
allotments (provided space is made available) in the neighbourhood of
urban areas, where it is now the practice to burn most of the vegetable
waste. How rapidly the system can be introduced into the farming systems
of the Occident is a question to which no answer can be given until the
ideas in this book have been fully tried out in western agriculture. It
is not impossible that they may founder for a time on the present high
cost of labour. The method however is in full accord with the
well-marked tendency in western agriculture towards a more intensive
production. The inevitable change over from extensive to intensive
methods has already begun. For production to be more economical, the
acre yield must be increased. Already in the United States the
suggestion has been made that the line of advance in crop production
lies in restricting the area cultivated. A portion of the impoverished
prairie lands should go back to grass. The crops needed should be raised
from a smaller area. These ideas will become practicable the moment the
farmer learns how to utilize the waste products of his fields in
increasing the fertility of the soil. This is the greatest need of
agriculture at the present day.
BIBLIOGRAPHY
CLARKE, G.--'Some Aspects of Soil Improvement in Relation to Crop
Production,' Proc. of the Seventeenth Indian Science Congress, Asiatic
Society of Bengal, Calcutta,1930, p. 23.
DUCKER, H. C.--'Soil Erosion Problems of the Makwapala and Port Herold
Experiment Stations, Nyasaland,' Empire Cotton Growing Review, 8, 1931,
p. 1O.
FELSINGER, E. O.--'Memorandum on a System of Drainage Calculated to
Control the Flow of Water on Up-country Estates, with a view to
reducing Soil Erosion to a Minimum,' Tropical Agriculturist, 71, 1928,
p. 221; 74, 1930, p. 68.
HOWARD, A.--Crop Production in India, a Critical Survey of its Problems,
Oxford University Press, 1924.
HOWARD, A. and HOWARD, G. L. C.--The Development of Indian Agriculture,
Oxford University Press, 1929.
KING, F. H.--Farmers of Forty Centuries or Permanent Agriculture in
China, Korea and Japan, London, 1926.
LIPMAN, J. G.--'Soils and Men,' Proc. of the Inter. Congress on Soil
Science, Washington, D.C., 1928, p. 18.
MATTHAEI, L. E.--'More Mechanization in Farming, International Labour
Review, Geneva, 23, 1931, p.324.
PERCY, LORD EUSTACE--Education' at the Cross Roads, London, 1930.
Report of the Royal Commission on Agriculture in India Calcutta, 1928.
RIDDELL, W. A.--'The Influence of Machinery on Agricultural Conditions
in North America,' International Labour Review, Geneva, 13, 1926, p.
309.
WAGNER, W.--Die Chinesische Landwirtschaft, Berlin, 1926, p 222.
Chpater II
ORGANIC MATTER AND SOIL FERTILITY
The ancients and the moderns are in the completest agreement as to the
importance of organic matter in maintaining the fertility of the soil.
This is evident when the methods of crop production in the time of the
Romans are compared with the views now held by many of the leading
experiment station workers in the United States and other parts of the
world. In Roman times, the management of the manure heap had already
reached an advanced stage. In 40 B.C. Varro drew attention to the great
importance of the complete decay of manure before it was applied to the
land. To bring this about, the manure heap, during the period of
storage, had to be kept moist. In A.D. 90 Columella emphasized the
importance of constructing the pits (in which farmyard manure was
stored) in such a manner that drying out was impossible. He mentions the
need of turning this material in summer to facilitate decay, and
suggested that ripened manure should always be used for corn, while the
fresh material could be applied with safety to grass land. The Romans
therefore not only understood the importance of organic matter in crop
production but had gone a long way towards mastering the principle that,
to obtain the best results, it is necessary to arrange for the decay of
farmyard manure before it is applied to arable land. It is interesting
to turn from the writings of the ancients to the account of the
symposium on 'Soil Organic Matter and Green-manuring' arranged by the
American Society of Agronomy at Washington D.C. on 22 November 1928, the
main results of which appeared in the Journal of the American Society of
Agronomy of October 1929. Without exception, the investigators who took
part in this conference laid the greatest emphasis on the importance of
keeping up the supply of organic matter in the soil, and on discovering
the most effective and the most economical method of doing this under
the various conditions, as regards moisture, which the soils of the
United States present.
During the 2,000 years which have elapsed since Varro wrote in 40 B.C.
and the American investigators met in 1928, there has occurred only one
brief period during which the role of organic matter was to some extent
forgotten. This took place after Liebig's Chemistry in its Application
to Agriculture and Physiology first appeared in 1840. Liebig emphasized
the fact that plants derive their carbon from the carbon dioxide of the
atmosphere and advanced the view that, in order that a soil may remain
fertile, all that is necessary is to return to it, in the form of
manure, the mineral constituents and the nitrogen that have been taken
away in the crop. The discovery of the true origin of the carbon of
plants not unnaturally suggested that the organic matter in the soil was
of little consequence. Nitrogen and minerals only remained, the latter
being found in the plant ashes. When therefore analyses of the crops had
been made, it would be possible to draw up tables showing the farmer
what he must add in the way of nitrogen and minerals in any particular
case. These views and the controversies to which they gave rise,
combined with the results of the Rothamsted experiments (started by
Lawes and Gilbert in 1843) led to the adoption of artificial manures by
many of the farmers of Europe. The Rothamsted experiments undoubtedly
proved that if the proper quantities of combined nitrogen, phosphates
and potash are added to the soil, satisfactory crops for many years can
be obtained without the addition of organic matter beyond that afforded
by the roots of the crops grown. Further, the results of hundreds of
trials, in the course of ordinary farming practice, confirmed the fact
that the judicious addition of nitrogenous artificial fertilizers can,
in the great majority of cases, be relied on to increase the yield. It
was only natural that results of this kind, combined with the important
fact that the application of artificials often pays in practice,
produced a marked effect on current opinion and also on teaching. For
nearly a century after Liebig's ideas first appeared, the majority of
agricultural chemists held that all that mattered in obtaining maximum
yields was the addition of so many pounds of nitrogen, phosphorus and
potassium to the acre. Beyond this the only other factor of importance
was the liming of acid soils. The great development of the artificial
manure industry followed as a matter of course.
The place of organic matter in the soil economy was forgotten. The old
methods of maintaining soil fertility naturally fell into the
background.
For a time all seemed to go well. It is only in comparatively recent
years that experiment station workers have begun to understand the part
played in crop production by the micro-organisms of the soil and to
realize that the supply of artificials is not the whole story. Something
more is needed. The need for the maintenance of the supply of organic
matter soon became apparent. The view now beginning to be held is that,
only after the supply of organic matter has been adequately provided
for, will the full benefit of artificials be realized. There appears to
be a great field for future experiment in the judicious use of
artificials to land already in a fair state of fertility.
In all this however there was one important exception. In the Orient,
the artificial manure phase had practically no influence on indigenous
practice and passed unheeded. The Liebig tradition failed to influence
the farmers of forty centuries. No demand for these products of the west
exists in China. At the present day it would be difficult to purchase
such a substance as sulphate of ammonia in the bazaars of rural India.
SOIL HUMUS, ITS ORIGIN AND NATURE
What is the origin and nature of the organic matter or soil 'humus' and
what part does it play in soil fertility? These matters form the subject
of the present chapter.
NOTE: In the presentation which follows, the fullest use has been made
of (1) one of the papers of Waksman (Paper No. 276 of the Journal
Series, New Jersey Agricultural Experiment Station, Department of Soil
Chemistry and Bacteriology, afterwards published in Soil Science, 22,
1926, p. 123) and (2) of the symposium on soil organic matter and
green-manuring which appeared in the issue of the Journal of the
American Society of Agronomy of October 1929. These important
contributions to the subject have made it easy briefly to sketch the
necessary scientific background for the presentation of the Indore
process.
The organic matter found in the soil consists of two very different
classes of material: (1) the constituents of plants and animals which
have been introduced into the soil and are undergoing decomposition;
various unstable intermediate products which have been formed under
certain environmental conditions; substances like lignified cellulose
which are more resistant to decomposition and which may persist in the
soil for some time; and (2) number of valuable materials which have been
synthesized by the numerous groups of micro-organisms which form the
soil population. The soil organic matter is thus a heterogeneous mass of
substances which is constantly undergoing changes in composition. When
its composition reaches a certain stage of equilibrium, it becomes more
or less homogeneous and is then incorporated into the soil as 'humus'.
This definition of soil organic matter, which is due to Waksman, is of
great importance. Soil organic matter or 'humus' is not merely the
residue left when vegetable and animal residues decay. It contains in
addition the valuable materials synthesized and left behind by the fungi
and bacteria of the soil population. Moreover it is a product of the
general soil conditions which obtain in any particular locality, and
therefore varies in composition and character from one soil type to
another. It is not the same all over the world. The soil humus for
example of the black cotton soils of India is not identical with that of
the alluvium of the Indo-Gangetic plain.
The various steps in the formation of soil organic matter are somewhat
as follows. When the fresh remains of plants or animals are added to the
soil, a portion of this organic matter is at once attacked by a large
number of the micro-organisms present. Rapid and intense decomposition
ensues. The nature of these organisms depends on the soil conditions
(mechanical and chemical composition and physical condition) and on the
soil environment (moisture content, reaction and aeration, and the
presence of available minerals). The decomposition processes can best be
followed by measuring one of the end-products of the reaction--carbon
dioxide. The rate of evolution of this gas depends on the nature of the
organic matter, on the organisms which take part in the process and on
the soil environmental conditions. As soon as the readily decomposable
constituents of the plant and animal remains (sugars, starches, pectins,
celluloses, proteins, amino-acids) have disappeared, the speed of
decomposition diminishes and a condition of equilibrium tends to become
established. At this stage only those constituents of the original
organic matter, such as the lignins which are acted upon slowly, are
left. These and the substances synthesized by the micro-organisms
together form the soil humus and then undergo only a slow transformation
during which a moderate but constant stream of carbon dioxide is
liberated. At the same time the nitrogen of this soil humus is similarly
converted into ammonia which, under favourable conditions, is then
transformed into nitrate. It will be clear therefore that the soil
organic matter or humus is a manufactured product and that its
composition is not everywhere the same, but will vary with the soil
conditions under which it is produced. Like all manufactured articles,
it must be properly made if it is to be really effective. Too much
attention therefore cannot be paid to its preparation.
After the production of humus and its incorporation into the soil mass,
the next step is its utilization by the crop. This can only take place
when this organic matter is decomposed by the micro-organisms of the
soil. This process is very slow, as can be seen by placing a quantity of
soil under favourable environmental conditions and measuring the rate of
decomposition, either by the evolution of carbon dioxide or by the
accumulation of ammonia and nitrate nitrogen. Since the ratio between
the carbon and nitrogen content of the humus in normal cultivated soils
is more or less constant, approaching 10:1, the evolution of carbon
dioxide will be accompanied by the liberation of available nitrogen.
This oxidation of the carbon and of the nitrogen is comparatively very
slow, as only slow-growing groups of microorganisms are capable of
attacking it. These organisms are aerobic and moreover can only work
effectively when the general soil reaction is favourable. Their
activities are therefore hastened in non-acid peat soils by draining, in
acid peat soils by draining and liming, and in acid soils by liming.
It will be clear that the utilization of vegetable and animal wastes in
crop production involves two definite steps: (1) the formation of humus
and its incorporation into the soil and (2) the slow oxidation of this
product accompanied by the production of available nitrogen. Both of
these stages are brought about by micro-organisms for which suitable
environmental conditions are essential. The requirements of the first
phase--the preparation of humus and its incorporation into the soil
mass--are so intense that if the process takes place in the soil itself,
it is certain to interfere with the development of the crop. The needs
of the second phase--the utilization of humus--are much less intense and
can proceed in the soil without harm to the growing plant. From the
point of view of crop production therefore, it will be a distinct
advantage to separate these two stages and to prepare the humus outside
the field. In this matter the Chinese have anticipated the teachings of
western science. The cultivators of the Orient were the first to grasp
and act upon the master idea that the growth of a crop involves two
separate processes, the preparation of food-materials from vegetable and
animal wastes which must be done outside the field, and the actual
growing of the crop. Only in this way can the soil be protected from
overwork
THE FORMATION OF HUMUS AS A RESULT OF THE SYNTHESIZING ACTIVITIES OF
MICRO-ORGANISMS
Although the important part played by microorganisms in the formation of
soil humus has only very recently been fully understood, nevertheless
the older literature contains a number of useful contributions
to the subject. Most of these early papers appeared towards
the end of the last century; many of them related to other branches
of knowledge and were not written from the point of view of agriculture.
They have been summed up by Waksman, from whose paper the
following account has been prepared. Post-Ramann and Muller considered
that the 'humus' bodies obtained from soil often consist of the
chitinous remains of insects and animal excrete. Wettstein and
Winterstein showed that chitin is characteristic of various fungi and
not of bacteria. Schmook advanced the view that the protein nitrogen in
the soil was mostly present in the bodies of bacteria and protozoa.
Trussov showed that the protoplasm of fungi is a source of humus in the
soil. Schreiner and Storey suggested that various characteristic
constituents of the soil are probably synthesized by micro-organisms.
The earlier work on this subject has been considerably developed, first
by Falck and more recently by Waksman. Falck showed that organic matter
in forest soils can be transformed into different types of humus in at
least three ways: (1) The yearly additions of raw organic matter are
completely decomposed by fungi (microcriny) accompanied by the synthesis
of fungus protoplasm, which serves as an excellent fertilizer for the
forest trees. In this process the celluloses are decomposed completely,
whereas the lignins are more resistant. (2) The decomposition of the
organic matter is begun by fungi and then carried on by lower
invertebrates and bacteria (anthracriny). The fungus mycelium as well as
the original organic matter are devoured by various larvae producing a
dark 'humus' mass which, in the presence of bases, is oxidized by
bacteria with the ultimate liberation of carbon dioxide and the
formation of nitrate. (3) The formation of peat (anthrogeny), which
Falck explains as resulting from the absence of an abundant fungus
development. Waksman carried the subject still further and called
attention to the similarity between the carbon-nitrogen ratio of the
soil organic matter and that of the protoplasm of the soil fungi and
other micro-organisms, and suggested that these probably make up a large
part of the soil 'humus'. He further pointed out that when cellulose is
added to the soil, it decomposes only in proportion to the available
combined nitrogen present. This is because the decomposition is brought
about by fungi and bacteria, both of which require combined nitrogen.
The ratio between the amount of cellulose decomposed and the nitrogen
required is about 30:1, so that, for every thirty parts of cellulose
decomposed by the fungi and bacteria, one part of inorganic nitrogen
(ammonium salt or nitrate) will be built up into microbial protoplasm.
In the presence of sufficient combined nitrogen and under aerobic
conditions, the decomposition of cellulose is very rapid. The same is
true of vegetable wastes like straw, maize stalks, wood products and
other materials rich in celluloses, pentosans and lower carbohydrates
but poor in nitrogen. These facts explain the injurious effects on crop
growth which follow the addition of straw and green-manure to the soil.
The decomposition of these materials removes large quantities of
combined nitrogen from the soil solution. This nitrogen is then
temporarily stored in the form of microbial protoplasm, when for a time
it is placed beyond the reach of the growing crop.
Since Waksman's paper appeared in 1926, an important contribution to
this subject has recently been made by Phillips, Weite and Smith. The
results of these investigators (which agree with our experience at
Indore) has removed the impression that lignin is comparatively
resistant to the action of micro-organisms. Under suitable conditions,
soil organisms are capable of decomposing lignin as found in lignified
plant materials (cornstalks, oat hulls, corn cobs and wheat straw), the
rate of decomposition being as great as that of cellulose and pentosans.
THE ROLE OF HUMUS IN THE SOIL
From the immediately practical point of view, the actual role of humus
in the soil is of even greater interest than its formation, nature and
decomposition. This material influences soil fertility in the following
ways:--
1. The physical properties of humus exert a favourable influence on the
tilth, moisture-retaining capacity and temperature of the soil as well
as on the nature of the soil solution.
2. The chemical properties of humus enable it to combine with the soil
bases, and to interact with various salts. It thereby influences the
general soil reaction, either acting directly as a weak organic acid or
by combining with bases liberating the more highly dissociating organic
acids.
3. The biological properties of humus offer not only a habitat but also
a source of energy, nitrogen and minerals for various micro-organisms.
These properties--physical, chemical and biological--confer upon humus a
place apart in the general work of the soil including crop production.
It is not too much to say that this material provides the very basis of
successful soil management and of agricultural practice.
THE WASHINGTON SYMPOSIUM ON SOIL ORGANIC MATTER
Once the origin and nature of the soil organic matter is understood and
the importance of this material in soil fertility is appreciated, the
next step is to consider how best to make use of this information and to
weld it into farming practice. With this object in view a symposium on
soil organic matter and green-manuring was arranged at Washington D.C.
on 22 November 1928, when the following papers were read and
discussed:--
I. 'The Relation of Soil Type to Organic Matter.' C. F. Marbut.
2. 'Organic Matter Problems in Humid Soils.' T. Lyttleton Lyon.
3. 'Organic Matter Problems Under Dry-Farming Conditions.' J. C. Russell
4. 'Organic Matter Problems in Irrigated Soils.' P. S. Burgess.
5. 'Chemical and Microbiological Principles Underlying the Use of
Green-Manures.' S. A. Waksman (by title only).
6. 'Influence of Organic Manures on the Chemical and Biological
Properties of Arid Soils.' J. E. Greaves.
7. 'Green-Manuring and Its Application to Agricultural.' A. J. Pieters
and Roland McKee.
In dealing with the question of organic matter in humid soils, Lyon
first presented a critical survey of the literature dealing with the
losses of nitrogen in soils and concluded that:--
1. The loss of gaseous nitrogen may, under some conditions, cause a
greater removal of nitrogen from a soil than occurs through absorption
by crop plants.
2. The conditions which favour a large loss of this kind are: (a)
tillage or stirring the soil in any way, (b) absence of plant growth,
(c) high nitrogen content of a soil, (d) application of large quantities
of nitrogenous manures, and (e) possibly the application of lime to some
soils.
3. The loss of gaseous nitrogen does not take into account the amount
fixed by soil organisms and therefore the calculated losses are less
than actually occurred.
These losses of gaseous nitrogen from the soil may arise in five
possible ways:--
1. There may be an escape of part of the ammonia during the process of
ammonification.
2. There may be a reduction of nitrates to form nitrogen as a result of
alternating oxidation and reduction.
3. There may be a loss of gaseous nitrogen in the oxidation of ammonia
to nitrous acid since nitrogen is possibly an intermediate product in
this process.
4. A loss of nitrogen may result from the interaction of nitrous acid
with the NH2 group of the amino-acids.
5. A loss of gaseous nitrogen may occur as a result of the decomposition
of ammonium nitrite in the process of nitrification.
In connexion with these losses of nitrogen it was pointed out in the
discussion that the following two facts must be considered: (1) The
ratio of carbon to nitrogen in the soils of the humid regions tends to
maintain itself in the region of 10:1. If the organic residues left in
the soil or applied to it afterwards have a higher carbon-nitrogen ratio
than 10:1, an adjustment is soon effected, the extra carbon disappearing
into the atmosphere as carbon dioxide. If the carbon-nitrogen ratio is
less than 10:1, there is likely to be a loss of nitrogen before the
ratio is adjusted. (2) The nitrogen content of any given soil tends to
come to an equilibrium at a point which depends upon the nature of the
soil, the effective climate and the cropping system. When therefore the
nitrogen supply is increased in any way, the excess is soon dissipated
when the soil comes under cultivation.
The information placed before the meeting by Russel (Nebraska) on the
role of organic matter under dry-farming conditions was most
instructive, and throws a flood of light on the consequences which are
certain to follow the continuous cropping of virgin land without manure.
A rapid and continuous fall in the total organic matter content,
accompanied by loss of nitrogen, occurs together with a corresponding
falling off in cropping power. Side by side, the water-holding capacity
of these soils decreases, while the structure and tilth exhibit marked
degeneration. All this has naturally led to attempts being made to
restore the original content of organic matter. The results obtained,
however, have been most disappointing, for the reason that most of these
efforts have been directed towards the direct incorporation of
green-manures and raw organic matter like straw into the soil under
conditions of low rainfall. In many cases more harm than good has
resulted. Russel concludes that the problem of the restoration of
organic matter under dry-land conditions is extremely complicated and
difficult and leans to the view that the solution of the problem might
after all be found in the direction of nitrogenous fertilizers.
Experience at Indore, however, suggests that all these difficulties
could at once be avoided if the available supplies of green-manure,
straw and other raw organic matter could first be composted outside the
field before being applied to the land. The American farmers are
obviously trying to overwork the soil and Mother Earth naturally
objects.
The application of organic matter to the soil is followed by a number of
important indirect results. These were dealt with by Greaves in a most
interesting communication, in which the results obtained over a number
of years on two different types of Utah soils were discussed. The first
(Nephi) was typical dry-farm soil, the second was under irrigation
(Greenville). In both the results were similar. The application of
organic matter increased the ammonifying, nitrifying and nitrogen fixing
processes of the soil. The gains in nitrogen, due to non-symbiotic
nitrogen fixers, occurring under greenhouse conditions, varied from 0 to
304 lb. per acre foot of soil. The greatest gains occurred when legumes
were used in the manure. The gain occurring in the soil under field
conditions, and attributed to non-symbiotic nitrogen fixation, was 44
lb. per acre annually. Approximately 3,000 lb. of applied organic
material were decomposed every year.
The last paper of the symposium dealt with the practice of
green-manuring throughout the United States, with the various crops
which are turned under, and with the great need for further exact
experimentation on this question. Pieters and McKee state: 'In reviewing
the experimental work that has been done with green-manures in the
United States and the practices that are now followed it is evident that
much work remains to be done before many questions can be settled or
answered. Some of these fall clearly in the field of chemistry, others
in physiology, and still others in bacteriology or other specialized
fields of biology. Some, however, are strictly agronomic problems or so
directly involved with crop production that their solution can perhaps
best be undertaken by the agronomist or carried on with his active
co-operation. It takes but a hasty survey to indicate the wide scope
this work must cover in order to answer the specific questions for the
many soil types, various climatic conditions, and for each of the large
number of agronomic and horticultural crops involved.' In no case is
there any reference in this paper to the growing of green-manures for
the express purpose of providing material for composting, possibly
because the need for this material has not yet been fully realized and
because of the labour involved. Green-manuring in the United States, as
in India and other parts of the world, is still in the empirical stage.
Green crops are grown merely to provide a supply of organic matter for
turning into the soil. What happens afterwards is a matter of chance. If
the results are favourable, so much the better; if anything untoward
occurs, one must hope for better things next time. That such an
uncertain practice persists at all in the United States and that it
appears to be spreading can only be explained by the great need of these
depleted soils for fresh supplies of organic matter.
BIBLIOGRAPHY
LIEBIG, J.--Chemistry in its Application to Agriculture and Physiology,
1840.
PHILLIPS, M., WETTE, H. D., and SMITH, N. R.--The Decomposition of
Lignified Materials by Soil Microorganisms,' Soil Science, 30, 1930, p.
383.
RUSSELL, E. J.--Soil Conditions and Plant Growth, London, 1927.
RUSSELL, E. J. and RICHARDS, E. H.--'The Changes taking place during the
Storage of Farmyard Manure,' Journ. Of Agric. Science, 8, 1917, p. 495.
'Symposium on Soil Organic Matter and Green-Manuring,' Journ. of the
American Society of Agronomy, 21, 1929, p. 943
WAKSMAN, S. A.--'The Origin and Nature of the Soil Organic Matter or
Soil "Humus": 1--Introductory and Historical,' Soil Science, 22, 1926,
p. 123.
Chapter III
THE SOURCES OF ORGANIC MATTER
A number of sources of soil organic matter exist, namely: (1) the roots
of crops left behind at harvest, including the weeds turned under in the
course of cultivation; (2) the algae met with in large quantities in
rice fields, on the surface of the soils of tropical countries during
the rainy season and to some extent in all soils; (3) green-manure; (4)
farmyard manure; (5) artificial farmyard manure. In addition to these
supplies, certain by-products of industries, such as oil-cakes and
wool-waste, are also employed as sources of organic matter. These,
however, are small in total amount and need not be considered. Except in
China and Japan and to a limited extent in India, little or no use is
made of night soil in crop production.
THE ROOT-SYSTEMS OF CROPS
It is not always realized that about half of every crop--the
root-system--remains in the ground at harvest time and thus provides
automatically a continuous return of organic matter to the soil. The
weeds and their roots turned in during the ordinary course of
cultivation add to this supply. When these residues, supplemented by the
fixation of nitrogen from the atmosphere, are accompanied by skilful
soil management, crop production can be maintained at a moderate level
without the addition of any manure whatsoever. A good example of such a
system of farming without manure is to be found on the alluvial soils of
the United Provinces, where the field records of ten centuries prove
that the land produces fair crops year after year without any falling
off in fertility. A perfect balance has been reached between the
manurial requirements of the crops harvested and the natural processes
which recuperate fertility. A similar, although not so striking a
result, is afforded by the permanent wheat plot at Rothamsted, where
this crop has been grown every year on the same land without manure
since 1844. This plot, which has been without manure of any kind since
1839, showed a slow decline in production for the first eighteen years
after which the yield has been practically constant. Systems of soil
management such as these provide, as it were, the base line for the
would-be improver. Nothing exists in the world's agriculture below this
level. At the worst, therefore, the organic matter of a soil, constantly
cropped without manure, does not disappear altogether. The wheel of life
slows down. It does not stop.
SOIL ALGAE
One source of readily decomposable organic matter, which is available in
India just at the moment when the cold season crops need it, is to be
found in the shape of a thick algal film on the surface of cultivated
soils during the second half of the rains. This film has also been
observed in Africa, Ceylon and Java, and is probably universal during
the rainy season in all parts of the tropics. As is well known, there
are two periods in India when the crop is in greatest need of combined
nitrogen: (1) at the break of the monsoon in June and July, and (2) when
the cold season crops are sown in October after the rains. These latter
are planted at a time when the available nitrogen in the surface soil is
likely to be in great defect. The land has been exposed to heavy rain
for long periods; the surface soil is often waterlogged. Nitrates under
such conditions are easily lost by leaching and also by
de-nitrification. The conditions are therefore altogether unfavourable
for any approach towards an ample supply of nitrate when sowing time
comes round in early October. How do the cold weather crops obtain a
sufficient supply of this essential food material? It is more than
probable that the deficiency is made up for, in part at least, by the
rapid decay of the algal film (which also appears to be one of the
factors in nitrogen fixation) during the last cultivations preceding the
sowing of the cold weather crop in October. It is possible that some
changes may have to be made in soil management with a view to
stimulating the growth of this algal film. One of the beneficial effects
of growing a green-manure crop like sann hemp for composting, during the
early rains, may prove to be due to the favourable environment provided
for the rapid establishment of the algal film. On monsoon fallow land it
will probably be found best to suspend surface cultivation during the
second half of the rains when the film is most active. There is already
among the cultivators of India a tendency to stop stirring the surface,
from the middle to the end of the rains, even when this involves the
growth of weeds. This coincides with the period when the algal film is
most noticeable. The indigenous practices may therefore prove to be
based on sound scientific principles. Here are ready to hand several
interesting subjects which urgently call for study under actual tropical
conditions. When this is undertaken, the investigation should include:
(1) the conditions most favourable for the establishment of the algal
film; (2) the part played by algae and associated bacteria in nitrogen
fixation; (3) the role of algae in banking easily destroyed combined
nitrogen during the rains; and (4) the supply of easily decomposable and
easily nitrifiable organic matter for the use of the cold weather crops.
In the rice fields of the tropics, the algal carpet is even more evident
than on ordinary cultivated soils. The total weight of organic matter
added every year to each acre of rice land in the shape of algal remains
must be considerable and must serve as a useful addition to the store of
organic matter. Apart from the fixation of nitrogen from the air, it may
help to explain why such heavy crops of paddy can be obtained in India,
year after year on the same land, without manure.
GREEN-MANURES
Since the investigations of Schulz-Lupitz first showed how open sandy
soils in Germany can be rapidly improved in texture by the incorporation
of green-manures, the future possibilities of this method of enriching
the land became apparent to the investigators of the Occident. After the
role of the nodules (found on the roots of leguminous plants) in the
fixation of atmospheric nitrogen was proved, the problems of
green-manuring have naturally centred round the utilization of the
leguminous crop in adding to the store of organic matter and combined
nitrogen in the soil. At the end of the last century it seemed so easy,
by merely turning in a leguminous crop, to settle at one stroke and in a
very economical fashion the great problem of maintaining soil fertility.
At the expenditure of a very little trouble, the soil might be made to
manure itself. A supply of combined nitrogen, as well as a fair quantity
of organic matter, might be provided without any serious interference
with ordinary cropping. These expectations have led to innumerable
green-manuring experiments all over the world with practically every
species of leguminous crop. The results however have left much to be
desired. In a few cases, particularly on open soils and where the
rainfall, after the ploughing in of the green crop, is well distributed,
the results have been satisfactory. On rice lands, where abundance of
water ensures the maintenance of swamp conditions, somewhat similar
results have been obtained. In the vast majority of cases, however.
green-manuring has been disappointing. As a general method of soil
improvement, the game is hardly worth the candle. On the monsoon fed
areas of India the rainfall is often so uncertain, after the green crop
is ploughed in, that for long periods decay is arrested. Sowing time
arrives at a stage when the soil contains a mass of half-rotted
material, with insufficient nitrogen and moisture for the growth of a
crop. Failure results. The crops raised after green-manure are worse
than those obtained on similar land left fallow. For this reason
green-manuring has not been taken up by the people in India, in spite of
the experiments and propaganda of the Agricultural Department.
It soon became evident, during the early years of the present century in
India, that no matter what the rainfall and the soil conditions may be,
a definite time factor is in operation in green-manuring. A period of
not less than eight weeks must elapse, between the ploughing in of the
green crop and the planting of the next, if satisfactory results are to
be obtained. This was well brought out in the green-manuring experiments
on tobacco, carried out at Pusa between 1912 and 1915. Some years later,
the explanation of this factor, as well as the general conditions
necessary for the decay of a green-manure crop were furnished by the
work done at the New Jersey experiment station by Waksman and his
co-workers. The decay and incorporation of green-manure in the soil has
been shown to be a very complex process, depending on: (1) the chemical
composition of the plants which make up the green-manure, which in turn
largely depends on the age of the crop when ploughed in; (2) the nature
of the decomposition of the various groups of organic complexes in the
plant by the different types of soil organisms, which in turn is
influenced by such factors as moisture, aeration, and the supply of
available nitrogen and phosphates needed by these organisms, and (3) the
metabolism of the microorganisms taking part in the decay of the green
crop.
The process of incorporation takes place on the following lines. When
the green-manure crop is ploughed in, the first stages of decay are
brought about by fungi, which require for their activities ample
supplies of air, moisture and combined nitrogen, as well as the soluble
and easily decomposable carbohydrates supplied by the green crop. If the
supply of nitrogen provided by the green-manure is insufficient, the
stores of soluble nitrates in the soil solution are utilized by the
fungi. Decay is rapid provided all these essential factors are
simultaneously arranged for. The result is that the whole energies of
the soil at this period are given up to the needs of the fungi of decay,
which synthesize large quantities of protoplasm from the materials
supplied by the green crop and the soil solution. During this phase,
most of the nitrogen present is built up into mycelial tissue, and is
therefore not immediately available for the growth of crops. The next
stage is the decay of the remainder of the green-manure, including the
mycelial tissue itself, by various groups of bacteria, followed by the
incorporation of the whole mass into the soil organic matter. This must
first be nitrified before the soil solution and the crop can obtain any
benefit from this form of manuring. Clearly all this takes time, and
needs abundance of oxygen as well as a continuous supply of soil
moisture. If any of the limiting factors--nitrogen supply, air or
moisture--are in defect, it is obvious that the final stage of
nitrifiable organic matter will not be quickly reached. The soil will
not only contain a mass of undigested material, but will be poor in
available nitrogen and perhaps low in moisture as well. Seeds sown in
such a soil can only result in a poor crop. The investigations of the
New Jersey experiment station explain the importance of the time-factor
in green-manuring, and incidentally show that the ordinary
green-manuring experiments in India cannot possibly succeed. The sooner
they are discontinued the better. Nothing is to be gained by attempting
the hopeless task of manufacturing soil organic matter under conditions
which cannot be controlled.
The question at once arises as to whether the green-manuring process
can be regulated in such a manner that the results can be relied upon? A
number of attempts have been made in this direction in India, of which
that carried out by Clarke at Shahjahanpur is the most promising. Green
crops of sann hemp (Crotalaria juncea L.) have been successfully
utilized for the growth of sugar-cane. The secret of the Shahjahanpur
process is to provide ample moisture, by means of irrigation, for the
first stages of the decay of the green-manure. The rainfall, after the
hemp crop is ploughed in, is carefully watched. If it is less than five
inches during the first fortnight of September, the fields are
irrigated. This enables the first phase of the decay of the green crop
by the soil fungi to be completed. Practically all the nitrogen is then
in the form of easily decomposable mycelial tissue. During the autumn,
nitrification is prevented by drying out the surface soil. The nitrogen
is, as it were, kept in the bank till the sugar-cane is planted under
irrigation in March. Nitrification then sets in and the available
supplies of combined nitrogen are made use of by the sugar-cane. In this
way crops of over thirty tons of cane to the acre have been grown
without the addition of any manure beyond the hemp, grown on the same
land the previous rains and treated in the manner indicated above. These
results do not appear to have been obtained with any other crop than
sugar-cane planted in March. It would be interesting to have figures for
wheat, sown in October, i.e. about six weeks after the hemp was ploughed
under. It is probable that even with irrigation, this interval is
insufficient for the proper incorporation of the green crop into the
body of the soil organic matter and its subsequent nitrification. In
this case, the Shahjahanpur method, valuable and interesting as it is,
can only have a limited application.
Is it possible to devise a method of green-manuring, by means of the
leguminous crop, which avoids all risks, is certain, and also makes the
fullest use of this system? There are two possible ways in which the
growing of a leguminous green-manure crop may benefit the soil. These
are: (1) the well-known advantages of such crops in the rotation in
increasing the nitrogen supply and in stimulating the micro-organisms in
the soil, and (2) the effects of incorporating the green crop into the
store of soil organic matter. Lohnis, however, showed, in many
green-manuring experiments with leguminous crops, that the same results
were obtained when the crop was removed as when it was ploughed under--a
conclusion which is in full accord with Waksman's work. It follows from
this that the double advantage of a leguminous green-manure crop can
only be achieved provided fall use of the crop itself can be found
outside the field, either as fodder for animals, for making silage or as
material for the manufacture of compost. This latter method has been
successfully worked out at Indore, and will be described in the next
chapter. The real place of the leguminous crop in green-manuring seems
to be in providing material for the manufacture of organic matter in a
compost factory, specially designed for the purpose.
The exact period in the life history of the green crop, when it should
be reaped for composting, is an important matter. If the crop is cut
before the grand period of growth is completed, the maximum amount of
vegetable waste will not be obtained. On the other hand, an early
harvest will yield a product rich in nitrogen and suitable for rapid
decay (Appendix C). Late harvesting is also attended with disadvantages.
If reaped after flowering begins, the green crop will have used up a
good deal of the rich nodule tissue which will then be temporarily
removed from the soil and will not benefit the next crop. Further, the
older the crop, the more unfavourable the carbon-nitrogen ratio becomes.
The best stage for removal will be just before flowering begins. At this
point, most of the nitrates in the soil solution have been absorbed by
the crop and have been banked, either in the form of an easily
decomposable root-system or as compost material, the chemical
composition of which is exactly what is needed to improve the
carbon-nitrogen ratio of the other vegetable wastes of the farm. When
the green crop is reaped at this stage the following advantages are
obtained: (1) The nitrates of the soil solution are safely banked. (2)
The next crop derives the maximum benefit from an easily decomposable
and uniformly distributed root-system, rich in combined nitrogen, the
decay and incorporation of which is well within the powers of the soil.
(3) The store of vegetable waste for composting is increased in amount
and improved in chemical composition by the uniform distribution of the
combined nitrogen throughout the tissues of the green crop.
FARMYARD MANURE
From the beginning of agriculture, the utilization of farm wastes,
rotted by means of the urine and dung of animals, has been the principal
means of replenishing soil losses. Even at the present day, in spite of
the establishment of numerous experiment stations and the employment of
an army of investigators, the methods in vogue in the preparation and
storage of this product leave much to be desired. Even under the
covered-yard system, when the dung and litter are left under the animals
until a layer several feet thick is produced, and the product is
protected from the weather, as much as fifteen per cent of the valuable
nitrogen is lost. When the dung is carted out into a heap to ripen, as
is the usual practice, the losses of nitrogen are even greater. Russell
and Richards, who some years ago carried out an elaborate investigation
on the storage of farmyard manure at Rothamsted, concluded that: (1) the
system of leaving the manure under the beasts till it is required for
the fields, as in the box or covered-yard system, is the best whenever
this is practicable; (2) the ideal method of storage is under anaerobic
conditions at a temperature of 26 degrees C.; (3) the manure heap, however
well made and protected, involves losses of nitrogen; and (4) the best
hope of improvement lies in storing the manure in watertight tanks or
pits, so made that they can be completely closed and thereby allow the
attainment of perfect anaerobic conditions. These investigations,
published in 1917, clearly indicate that one of the reasons for the
present imperfect management of farmyard manure lies in the fact that
the conditions are sometimes aerobic, at others anaerobic, whereas they
should be one or the other throughout. In other words, there is no
proper management of the air supply. Moisture is not usually in defect,
except in hot countries like India where there is abundant air but often
little moisture. Taking Great Britain and India as extreme cases of the
management of farmyard manure, we find one or other of the following
conditions in operation. In Great Britain, the irregular air supply of
the manure heap leads to serious losses of nitrogen.
The final product is not a fine powder but a partially rotted material,
which cannot be incorporated into the pore-spaces of the soil until
further decay has taken place. The soil therefore has to do a good deal
of work before the farmyard manure, applied on the surface in lumps, can
be uniformly distributed through and incorporated into the soil mass. In
India, the storage of farmyard manure leads to the loss of so much
moisture, that often insufficient decay takes place before it finds its
way into the soil. Losses of nitrogen may be prevented in this way but
the work thrown upon the soil is even greater than in temperate regions.
Only in China and Japan is any real attempt made to prepare the manure
for the use of the crop, and to relieve the soil from unnecessary work.
What is needed throughout the world is a continuous system of preparing
farmyard manure in which (1) all losses of nitrogen are avoided, and,
(2) the various steps from the raw material to the finished product
follow a definite plan, based on the orderly breaking down of the
materials, and the preparation of a finished product, ready for
immediate nitrification, which can easily be incorporated into the soil.
At the same time, an attempt should be made to gain as much nitrogen as
possible by fixation from the atmosphere. Only when all this is done
will the preparation of farmyard manure be based on correct scientific
principles.
ARTIFICIAL FARMYARD MANURE
During the last ten years, an additional source of soil organic matter
has been utilized, namely, artificial or synthetic farmyard manure. In
1921, the results of experiments, carried out by Hutchinson and Richards
at Rothamsted on the conversion of straw into manure without the
intervention of live stock, were published. In this pioneering work,
which constitutes an important milestone in the development of crop
production, a method was devised by which straw could be converted into
a substance having many of the properties of stable manure. In the
preliminary experiments, the most promising results were obtained when
the straw was subjected to the action of a culture of an aerobic
cellulose decomposing organism (Spirochoeta cytophaga), whose activities
were found to depend on the mineral substances present in the culture
fluid. The essential factors in the production of well-rotted farmyard
manure from straw were found to be: air supply; a suitable temperature,
and a small amount of soluble combined nitrogen. The fermentation was
aerobic; the breakdown of the straw was most rapid in a neutral or
slightly alkaline medium in the presence of sufficient available
nitrogen. Urine, urea, ammonium carbonate and peptone (within certain
concentrations) were all useful forms of combined nitrogen. Sulphate of
ammonia by itself was not suitable, as the medium soon became markedly
acid. The concentration of the combined nitrogen added was found to be
important. When this was in excess, nitrogen was lost from the mass
before decay could proceed; when it was in defect, a marked tendency to
fix nitrogen was observed. The publication of this paper soon led to a
number of further investigations, and to numberless attempts all over
the world to prepare artificial farmyard manure from every kind of
vegetable waste. The principles underlying the conversion are now well
understood, and have recently been summed up by Waksman and his
co-workers in the Journal of the American Society of Agronomy (21, 1929,
p. 533) in a paper which should be carefully studied by all interested
in this important subject. The principles underlying the conversion are
so well put by these investigators that they are best given in the
authors' own words:--
'The problems involved in the study of the principles underlying
the decomposition of mature straw and other plant residues in
composts, leading to the formation of so-called artificial manure,
involve a knowledge of: (a) the composition of the plant
material; (b) the mechanism of the decomposition processes which
are brought about by the micro-organisms; and (c) a knowledge
of the metabolism of these organisms.
'Straw and other farm residues, which are commonly used for the
purpose of composting, consist predominantly (60 per cent or
more) of celluloses and hemi-celluloses, which undergo rapid
decomposition in the presence of aufficient nitrogen and other
minerals, of lignins (15 to 20 per cent) which are more resistant to
decomposition and which gradually accumulate, of water-soluble
substances (5 to 12 per cent) which decompose very rapidly, of
proteins which are usually present in very small amounts (2.2 to 30
per cent) but which gradually increase in concentration with the
advance of decomposition, and of the mineral portion or ash.
'The processes of decomposition involved in the composting consist
largely in the disappearance of the celluloses and hemi-celluloses,
which make up more than 80 per cent of the organic matter which
is undergoing decomposition in the process of formation of artificial
manures. These poly-saccharides cannot be used as direct sources
of energy by nitrogen-fixing bacteria and their decomposition
depends entirely upon the action of various fungi and aerobic
bacteria. In the process of decomposition of the celluloses
and hemi-celluloses, the micro-organisms bring about the synthesis
of microbial cell substance. This may be quite considerable, frequently
equivalent to a fifth or even more of the actual organic matter
decomposed. To synthesize these large quantities of organic matter,
the micro-organisms require large quantities of available nitrogen
and phosphorus and a favourable reaction. The nitrogen and phosphorus
are used for the building up of the proteins and nucleins in the
microbial cells. Since there is a direct relation between the
celluloses decomposed and the organic matter synthesized, it
should be expected also that there would be a direct relation between
the cellulose decomposed and the amount of nitrogen required.
As a matter of fact, for every forty or fifty parts of cellulose
and hemi-cellulose decomposed, one unit of available nitrogen has
to be added to the compost.
'As the plant residues used in the preparation of "artificial
manure" are poor in nitrogen, available inorganic nitrogen must
be introduced for the purpose of bringing about active decomposition.
This explains the increase in the protein content of the compost
accompanying the gradual decrease of the celluloses and hemi-celluloses.
'In general, artificial composts can be prepared from plant residues
of any chemical composition so long as the nature of these
residues and of the processes involved in their decomposition are
known. By regulating the temperature and moisture content and
by introducing the required amounts of nitrogen, phosphorus,
potassium and calcium carbonate, the speed of decomposition and
the nature of the product formed can be controlled.'
It is not possible in the space available to summarize all the various
experiments which have been made in Great Britain, the United States,
India and other parts of the world on the actual conversion of vegetable
residues into artificial farmyard manure. It will be sufficient to refer
to typical examples of what has been done. The Rothamsted investigations
have been continued and have led to a patented process, known as Adco,
by which the requisite nitrogenous and phosphatic food for the
micro-organisms, as well as a base for the neutralization of acidity,
are added to the vegetable wastes in the form of powders. Full details
and numerous illustrations are to be found in the various Adco
pamphlets. The object of patenting the process is not profit for the
inventors but the raising of funds for further research. All users of
Adco therefore are not only provided with a useful mixture but also make
a small contribution to the cost of fundamental research work. In India,
the various experiments on the production of artificial farmyard manure
from a large number of materials, such as prickly pear, fallen leaves,
town refuse, mahua (Bassia latifolia L.) flowers, weeds, banana waste,
leguminous plants such as sann hemp, green pea stalks and various weeds
have recently been summed up by Fowler, whose paper (see Bibliography
below) should be consulted for details. The materials employed for
adding the necessary nitrogen and other materials for the
micro-organisms were night-soil, cow-dung, cattle urine, activated
sludge or chemicals like sulphate of ammonia and calcium cyanamide. A
large number of experiments are described from which it is clear that
very useful manures, containing from 1 to 4 per cent of nitrogen, were
obtained, which in field trials with rice and maize gave results equal
to or better than any other nitrogenous manure in common use. Attempts
were made in the course of this work to determine the amount of nitrogen
fixation from the air which occurs during the conversion of the
vegetable waste. It was found, when proper care was taken to supply the
necessary organisms, that a considerable amount of free nitrogen was
actually absorbed. These results, which agree with others on the same
point, are of considerable interest. If in the conversion of vegetable
wastes into artificial farmyard manure additional nitrogen can be
gained, obviously the ideal conditions have been discovered. Once such
principles have been correctly ascertained and put into practice, it
might then be possible to deal not only with the manure heap itself but
also with green-manuring, so that actual fixation can be substituted for
the losses of nitrogen which now occur.
As is to be expected in such a matter as this, the preparation of
artificial farmyard manure has been in actual operation centuries before
Hutchinson and Richards began their work at Rothamsted. King, in Farmers
of Forty Centuries, describes the conversion by the Chinese peasants of
clover (Astragalus sinicus) into manure by mixing the green crop with
rich canal mud To all intents and purposes, this system closely
resembles the Adco process. Once more the empirical methods, discovered
during centuries of practice, have preceded the results obtained by the
application of pure science. Nevertheless, although in a sense the
Rothamsted workers have been anticipated, it is quite safe to say that
but for their work, the utilization of green clover in China, although
described in the literature of the subject, would have passed unheeded.
It was the novelty of the Rothamsted investigations which has proved so
useful and so stimulating.
A critical examination of the literature on the principles underlying
the conversion into humus of the chief groups of crude organic
matter--green-manure, farmyard manure and vegetable wastes--reveals one
fundamental weakness, namely, the fragmentation, into a number of
loosely related sections, of what is essentially one subject. Farmyard
manure, green-manure and the preparation of synthetic farmyard manure
are always dealt with as if they were separate things and not parts of
one great project. Even Waksman (whose contributions to the principles
underlying the conversion of vegetable wastes into humus cannot fail to
compel the admiration of all investigators), when the time came to write
up his work for the agronomists of the United States, contributed three
separate papers to the Journal of the American Society of Agronomy--one
on farmyard manure, one on green-manure and the third on artificial
farmyard manure--instead of synthesizing all these related subjects into
one single contribution. When we come to the practical side of the
question, a similar fragmentation is apparent. Green-manuring is always
a separate process. The manure heap and its utilization from the time of
the Romans to the present day, forms a special section of the work of
the farm. The manufacture of artificial farmyard manure is again split
off as an isolated operation. This particularism, in the most recent
papers, is reflected in the separate conversion of each kind of
vegetable waste, although it follows, from considerations of chemical
composition, that a mixture of residues is much more likely to possess a
suitable carbon-nitrogen ratio than any single material. As will be
evident from a study of Waksman's three papers referred to above, the
principles underlying the decay of farmyard manure, of green-manure and
the preparation of artificial farmyard manure are essentially the same,
namely, the synthesis of humus, by means of fungi and bacteria, from
crude vegetable matter, various nutrients, air, water and bases. This
humus increases the supply of soil organic matter and is capable of
rapid nitrification. What is needed is the welding of all the separate
fragments of the subject into a well ordered system. One process is
required, not several. The agriculturist of the future must be shown how
to become a chemical manufacturer. Further, the method finally adopted
must be so elastic that it can be introduced into almost any system of
agriculture. Again, it must be simple, safe and must yield a continuous
and uniform product, capable of being instantly utilized by the crop. No
waste of valuable nitrogen should occur at any stage. If possible,
matters should be so arranged that the fixation of atmospheric nitrogen
takes place at all stages of the process--in the compost factory and
afterwards in the soil. In the next chapter, a continuous process of
making humus is described which furfils the conditions just outlined.
This includes, in a single process, the various fragments of the
subject, such as the care of the manure heap, green-manuring, the
utilization of all vegetable wastes as well as the urine earth from the
cattle shed and the wood ashes from the labourers' quarters. By its
means, the waste products of 300 acres of land are converted every year
into about 1,OOO cart-loads of valuable humus, of uniform chemical
composition and of uniform fineness. When this material is added to the
soil there is a rapid increase in fertility. The practical results
obtained at Indore prove that all that is needed to raise crop
production to a much higher level throughout the world is the orderly
utilization of the waste products of agriculture itself.
BIBLIOGRAPHY
BRISTOL, B. M.--'On the Alga-flora of some dessicated English Soils:
an Important Factor in Soil Biology,' Annals of Botany, 34, 192O, P.35.
BRISTOL, M. B. and PAGE, H. J.--'A Critical Enquiry into the Alleged
Fixation of Nitrogen by Green Alga,' Annals of Applied Biology, 1O,
1923, p. 378.
BRISTor-ROACH, B. M.--'The Present Position of our Knowledge of the
Distribution and Functions of Alga, in the Soil,' Proc. of the Inter.
Congress of Soil Science, Washington, D.C., 1928, p. 30.
CARBERY, M. and FINLOW, R. S.--'Artificial Farmyard Manure,' Agric.
Jonrn. of India, 23, 1928, p. 80.
CLARKE, G., BANERJEE, S. C., NAIB HUSAIN, M., and QAYUM, A.--'Nitrate
Fluctuation in the Gangetic Alluvium and Some Aspects of the Nitrogen
Problem in India,' Agric. Journ. of India, 17, 1922, p. 463.
CLARKE, G.--'Some Aspects of Soil Improvement in relation to Crop
Production,' Proc. of the Seventeenth Indian Science Congress, Asiatic
Society of Bengal, Calcutta, 1930, p. 23.
DOBBS, A. C-' Green-Manuring in India,' Bull. 56, Agric. Research
Institute, Pusa, 1916.
FOWLER, G. J.--'Recent Experiments on the Preparation of Organic
Matter,' Agric. Journ. of India, 25, 1930, p 363.
HALL, A. D.--The Book of the Rothamsted Experiments, London, 1905.
HOWARD, A. and HOWARD, G. L. C.--'The Improvement of Tobacco Cultivation
in Bihar,' Bull. 50, Agric. Research Institute, Pusa, 1915.
HOWARD, A.--Crop Production in India, a Critical Survey of its Problems,
Oxford University Press, 1924.
HOWARD, A. and HOWARD, G. L. C.--The Application of Science to Crop
Production, an Experiment carried out at the Institute of Plant
Industry, Indore, Oxford University Press, 1929.
HUTCHINSON, H. B. and RICHARDS, E. H.--'Artificial Farmyard Manure,'
Journ. of the Min. of Agric. (London), 28, 1921, p. 398.
KING, F. H.--Farmers of Forty Centuries, or Permanent Agriculture in
China, Korea and Japan, London, 1926.
LOHNIS, F.--'Nitrogen Availability of Green Manures,' Soil Science, 22,
1926, p. 253.
LOHNIS, F.--'Effect of Growing Legumes upon succeeding Crops,' Soil
Science, 22, 1926, p. 355.
RUSSELL, E. J.--Soil Conditions and Plant Growth, London, 1927.
RUSSELL, E. J.--'The Present Status of Soil Microbiology,' Proc. of the
Inter. Congress on Soil Science, Washington, D.C., 1928, p. 36.
RUSSELL, E. J. and RICHARDS, E. H.--'The Changes taking place during the
Storage of Farmyard Manure,' Journ. of Agric. Science, 8, 1927, p. 495.
RUSSELL, E. J. and others.--The Micro-organisms in the Soil, London,
1923.
WAKSMAN, S. A.--'Chemical and Microbiological Principles underlying the
Decomposition of Green-Manures in the Soil,' Journ. of the Amer. Soc.
of Agronomy, 21, 1929, p. 1.
WAKSMAN, S. A., TENNEY, F. G. and DIEHM, R. A.--'Chemical and
Microbiological Principles underlying the Transformation of Organic
Matter in the Preparation of Artificial Manures,' Journ. of the Amer.
Soc. of Agronomy, 21, 1929, p.533.
WAKSMAN, S. A. and DIEHM, R. A.--Chemical and Microbiological
Principles underlying the Transformation of Organic Matter in Stable
Manure in the Soil,' Journ. Of the Amer. Soc. of Agronomy, 21, 1929,
p.795.
Chapter IV
THE MANUFACTURE OF COMPOST BY THE INDORE METHOD
The aim of the Indore method of manufacturing compost is by means of a
simple process to unite the advantages of three very different things:
(1) the results of scientific research on the transformation of plant
residues; (2) the agricultural experience of the past, and (3) the ideal
line of advance in the soil management of the future--in such a manner
that all the by-products of agriculture can be systematically converted
into humus. An essential feature of this synthesis is the avoidance of
anything in the nature of fragmentation of the factors. All available
vegetable matter, including the soiled bedding from the cattle-shed, all
unconsumed crop residues, fallen leaves and other forest wastes,
farmyard manure, green-manures and weeds pass systematically through
the compost factory, which also utilizes the urine earth from the floor
of the cattle-shed together with the available supply of wood ashes from
the blacksmith's shop and the workmen's quarters. The only other
materials employed are air and water. This manufacture is continuous
right through the year, including the rainy season, when a slight
modification has to be made to ensure sufficient aeration. The product
is a finely divided leaf-mould, of high nitrifying power, ready for
immediate use. The fine state of division enables the compost to be
rapidly incorporated and to exert its maximum influence on a very large
area of the internal surface of the soil.
The Indore process thus utilizes all the by-products of agriculture and
produces an essential manure. Besides doing this any successful system
of manufacturing compost must also fulfil the following conditions:--
1. The labour required must be reduced to a minimum. The process must
fit in with the care of the work cattle and with the ordinary working of
the farm.
2. A suitable and also a regular carbon-nitrogen ratio must be produced
by well mixing the vegetable residues before going into the compost
pits. Unless this is arranged for, decay is always retarded. The mixing
of these residues, combined with the proper breaking up of all
refractory materials is essential for rapid and vigorous fermentation
and for uniformity throughout the process.
3. The process must be rapid. To achieve this it must be aerobic
throughout, and must include arrangements for an adequate supply of
water and for inoculation, at the right moment, with the proper fungi
and bacteria. The general reaction of the mass must be maintained,
within the optimum range, by means of earth and wood ashes. The
maintenance of the proper relationship between air and water, so that no
delay takes place in the manufacture, proved to be the greatest
practical difficulty when evolving the process.
4. There should be no losses of nitrogen at any stage; if possible,
matters should be so arranged that fixation takes place in the compost
factory itself and afterwards in the field. To conserve the nitrogen,
the manufacture must stop as soon as the compost reaches the
nitrification stage, when it must either be used or banked. It can best
be used as a top dressing for irrigated crops; it can be preserved, as
money is kept in a bank, by applying it to the fields when dilution with
the large volume of soil arrests further changes till the next rains.
5. There must be no serious competition between the last stages of the
decay of the compost and the work of the soil in growing a crop. This is
accomplished by carrying the manufacture of humus up to the point when
nitrification is about to begin. In this way the Chinese principle of
dividing the growing of a crop into two separate processes--(1) the
preparation of the food materials outside the field, and (2) the actual
growing of the crop--can be introduced into general agricultural
practice.
6. The compost should not only add to the store of organic matter and
provide combined nitrogen for the soil solution but should also
stimulate the micro-organisms.
7. The manufacture must be a cleanly and a sanitary process from the
point of view both of man and also of his crops. There must be no smell
at any stage, flies must not breed in the compost pits or in the earth
under the work cattle. The seeds of weeds, the spores of harmful fungi,
the eggs of noxious insects must first be destroyed and then utilized as
raw material for more compost. All this is achieved by the combination,
in the compost pits during long periods, of high temperature and high
humidity with adequate aeration.
THE COMPOST FACTORY
The compost factory at Indore adjoins the cattle shed. This latter has
been constructed for forty oxen and is provided with a cubicle, in which
a supply of powdered urine earth can conveniently be stored. The cattle
stand on earth. A paved floor is undesirable as the animals rest better,
are more comfortable and are warmer on an earthen floor. The earth on
which the cattle stand absorbs the urine, and is replaced by new earth
to a depth of six inches every three or four months. The compost factory
(Plates III and IV show the cattle shed and compost factory) itself is a
very simple arrangement. It consists of thirty-three pits, each 30 ft.
by 14 ft. and 2 ft. deep with sloping sides, arranged in three rows with
aufficient space between the lines of pits for the easy passage of
loaded carts. The pits themselves are in pairs, with a space 12 ft. wide
between each pair. This arrangement enables carts to be brought up to
any particular pit. Ample access from the compost factory to the main
roads is also necessary, so that during the carting of the compost to
the fields, loaded and empty carts can easily pass one another, and also
leave room for the standing carts which are being filled. For a large
factory it is an advantage to have water laid on, so that the periodical
moistening of the compost can be done by means of a hose pipe. At
Indore, water is pumped through a 3 in. pipe into a pressed steel tank,
8 ft. by 8 ft. by 8 ft., holding 3,200 gallons, which is carried on walls,
4 ft. above the ground, to provide the necessary head. This supply lasts
about a week. Water is led by 1-1/2 in. pipes from the tank to eight taps,
to which the armoured hose can be screwed. Each tap serves about six pits.
The general arrangement will be clear from Plate IV.
The total cost of the water tank, including arrangements for
distribution, was Rs. 1650 (equivalent to about 120 pounds sterling). This
was made up as follows: tank, Rs. 750; pipe system, Rs. 466; girders for
tank, Rs. 31; armoured hose, Rs. 28: railway freight, Rs. 88; masonry
work, Rs. 148; labour, including fitting up, Rs. 129.
The space under the tank, which is walled in on three sides and is open
on the leeward side, is used for storing wood ashes, and for keeping the
tubs and implements needed for the making of compost.
For a smaller factory or for the small holder, such a water system is
not necessary. All that is needed is that the compost pits should be
arranged near a well.
COLLECTION AND STORAGE OF THE RAW MATERIAL
Plant Residues.--All vegetable wastes from the cultivated area--such as
weeds, cotton and other stalks, green-manure, cane-trash, fallen leaves
and so forth, and all inedible crop residues from the threshing
floor--are carefully collected. All woody materials like cotton and
pigeon-pea (Cajanus Indicus Spreng.) stalks are crushed by placing on
the farm roads to be trampled and reduced by the traffic to a condition
resembling broken up wheat straw (Plate V). All green materials--such as
weeds and green-manures--are withered for at least two days before use
or storage. All these various residues are stacked near the cattleshed
as received, layer by layer--if possible under cover during the
rains--so that these materials may become thoroughly mixed. Each layer
must not be more than one foot thick, otherwise difficulties arise in
making a suitable mixture. Care must also be taken to remove the stacked
material in vertical slices so as to ensure even mixture. Very hard and
woody materials--such as sugarcane and millet stumps, wood shavings,
sawdust and waste paper--should be dumped separately in one of the empty
compost pits with a little earth and kept moist. After this preliminary
treatment, these hard and resistant materials can be readily composted.
Steeping such materials in water for two days, before addition to the
bedding under the work cattle, serves the same purpose.
Urine Earth and Wood Ashes.--All the earth removed from the silage pits,
all earthy sweepings from the threshing floors and all silt from drains
are stored in a convenient place near the cattle-shed. This provides an
adequate supply of suitable earth for absorbing the urine of the work
cattle, and acting as a base in the making of compost. This earth is
spread evenly on the cattle-shed floor to a depth of six inches and
renewed every three or four months. Half the urine earth when removed
from the floor should be crushed (Plate VI) in a mortar mill(See Plate's
V and VI). to break up the large lumps, and should be stored under cover
as dry powdered urine earth. The other half of the urine earth should be
applied direct to the fields as manure. All available wood ashes should
be stored under cover, as in the case of the powdered urine earth. These
materials (urine earth and wood ashes) are as essential in the
manufacture of compost as the plant residues themselves.
Water and-Air. Both water and air are needed for the compost process,
which therefore must be carried out near a well or other source of fresh
water.
ARRANGEMENT AND DISPOSAL OF THE BEDDING UNDER THE WORK CATTLE
(All quantities in the following refer to one pair of oxen. The figures
should be multiplied, when necessary, by the number of pairs of oxen
kept.)
All the uneaten food and any damaged silage are thrown on the wet
portions of the cattle-shed floor. One and a half pals of stacked
vegetable refuse, together with not more than one-twentieth of this
amount of hard resistant material (such as wood shavings, sawdust or
waste paper) from the soaking pit are spread on the floor.
(A pal is a stretcher made of a piece of gunny sheet (4 ft. by 3 ft.)
nailed to two bamboos each 7 ft. 6 in. long.) The cattle sleep on
this bedding during the night. In this way the bedding gets crushed and
broken still further and also impregnated with urine. Next morning
one-fourthof a tagari of fresh dung is removed to the compost
pit; the rest of the cattle dung being scattered on the bedding
in lumps not bigger than a small orange; or this excess dung can
be made into cow-dung cakes (kundas) for fuel. (A tagari is a bowl made
of sheet iron, capacity five-sevenths of a cubic foot. In Table IV the
metal bowls are converted into pounds or double handfulls of the
materials used. Kundas, thin flat cow-dung cakes, about twelve inches in
diameter and one inch thick, are used in the villages of India as fuel
for the cooking of food.) Two-fifths of a tagari of dry urine earth is
sprinkled on the used bedding in the same manner as murum (Murum is the
Hindustani name of the permeable layer of decayed basalt which underlies
the black cotton soils of India) is spread on roads. The bedding is then
transferred by a spade on to the pal from one end to the other and
removed to the compost pit. In this way the raw material used for the
compost is made perfectly homogeneous. The earthen floor of the
cattle-shed should then be swept clean, the sweepings being removed on a
pal to the compost pit. All wet patches on the floor are covered with
new earth, after scraping out the very wet portions. In this way all
smell in the cattle-shed is avoided and the breeding of flies in the
earth underneath the animals is entirely prevented. Bedding for the next
day can then be laid as described above.
During the rains, the bedding should consist of three layers--a bottom
layer and a top layer of dry material specially reserved for the
purpose, any withered residues being sandwiched in between. On very wet
days, all the urine earth may be added to the bedding before removal to
the compost heap.
The volume and weight of the various materials which are moved to and
fro in the sheet-iron bowls (tagaries) are given in Table IV.
TABLE IV
VOLUME (IN DOUBLE HANDFULLS) AND WEIGHT (IN LB.)
OF THE CONTENTS OF A TAGARI
Volume in double handfulls Weight in lb.
Fresh dung 6.5 39.5
Powdered urine earth 20.5 22.5
Wood ashes 15 20
Fungus innoculant 6 20
Bacterial innoculant 6 20
Refractory vegetable residues 9
Mixed vegetable residues 9
Impregnated bedding 16.5
Sweepings from the cattles-shed floor 19
CHARGING THE COMPOST PITS
A convenient size for a compost pit is 30 ft. by I4 ft. and 2 ft. deep
with sloping sides. The depth of the compost pit is most important on
account of the aeration factor. It should never exceed 24 in. A wooden
tub, a rake, a bowl (tagari), and a few empty kerosine tins (each
holding four gallons) with handles are all that are needed besides the
pal.
The following materials are placed alongside each compost pit--powdered
urine earth, two fifths tagari, fresh dung, one-quarter tagari; fungus
material, three tenths tagari, taken from a compost pit ten to fifteen
days old; wood ashes, one twentieth tagari; water, one kerosine tin. The
wood ashes and one twentieth of a tagari of urine earth are mixed with
some dung and fungus material in a portion of the water to make a thin
slurry. The pals of bedding should be added, as they arrive, from one
edge of the pit by simply allowing the bamboo pole of the pal next the
pit to fall into it (Plate VII). The other pole is then lifted so that
the rest of the bedding drops easily into the pit. The material is then
spread by means of the rake in a layer, not exceeding two inches thick
over the compost pit. All trampling of the charged pit must be avoided
as this interferes with aeration. Some dry urine earth and then the
stirred slurry are first sprinkled thinly on each charge of bedding,
which should appear evenly wetted. The soaked residues from the tub are
then scattered on each layer of bedding. This inoculates the mass with
active fungus throughout. The polished surfaces of the bedding are also
covered with an active adherent coating. This leads to rapid and even
crumbling. The volume of the slurry is made up with more dung, fungus
starter and water as required. The pit is charged with the bedding,
layer by layer, until all the bedding is used up. The sweepings from the
cattle-shed floor, which are rich in urine, are sprinkled on the top of
each day's charge with a tagari, followed by one-third of a tin of fresh
water. This distributes the urine evenly throughout the daily charge and
also prevents excess drying. Another watering in the evening, with
two-thirds of a tin, and a third watering the next morning with
one-third of a tin completes the charge. The pit or a suitable portion
of it should be filled up to the brim in six days or less, the remaining
part being filled subsequently.
The period of charging must not exceed six days, whether or no the pit
is completely filled by then. Each six days' charge should be regarded
as one unit in the manufacture of compost, no matter whether the pit is
filled completely or not.
Everything is now ready for the development of an active fungus growth
(the first stage in the manufacture of compost). When properly managed,
a vertical section of the fermenting mass should appear quite uniform
and should not show any alternate layers.
As the pits are frequently full of water during the greater part of the
rains, the compost must be made in heaps from the middle of June to I
October. The dimensions of the heaps should not exceed 7 ft. by 7 ft. at
the top, 8 ft. by 8 ft. at the bottom and 2 ft. in height. The
dimensions of these monsoon heaps (any one of which is not necessarily
completed by the amount of vegetable waste which can be accumulated in
six days) must not be exceeded, otherwise aeration difficulties are
certain to be encountered. The decomposition in heaps during the rains
does not take place so evenly as in the pits.
During the early rains, all the material in the pits must be transferred
to heaps on the surface. This is most conveniently done at the time of
the first, second or third turn.
The subsequent waterings are most important, otherwise decay will stop.
The first watering is done twelve days (counted from the date on which
the filling of the pit begins) after charging, when 1.25 tins are added
evenly over the whole surface. Further water is added at the time of the
first, second and third turning and afterwards as needed. During the
rains, the quantity of water as given above must be added at the time of
charging; the subsequent waterings during the rains may be reduced or
completely omitted according to the weather. Stagnant rain-water from
the pits should never be used. When watering is done by a hose pipe from
a tank as at Indore, the amount added can easily be adjusted if the rate
of flow is known.
TURNING THE COMPOST
To ensure uniform mixture and decay, and to provide the necessary amount
of water and air as well as a supply of suitable bacteria, it is
necessary to turn the material three times. The only difficulty which is
likely to arise in the process is the establishment of anaerobic
conditions between the period of charging and the first turn. This can
be caused by overwatering or by want of attention to the mixing. It is
at once indicated by the smell and by the appearance of flies attempting
to breed in the mass. When this occurs, the heap should be turned at
once with the addition of dung slurry and wood ashes.
First turn. Sixteen days after charge (Plate IX). Sufficient fresh water
should be ready--about four tins according to the season. Three-fifths
of a tagari of compost is taken from another pit thirty days old (just
after the second turn) and scattered on the surface of the material.
This is necessary for inoculating the mass with the proper bacteria. The
top layer of the compost is then loosened and mixed, a portion at a
time, with a rake and well moistened with water. Half the heap is sliced
with a spade a few inches breadthwise and vertically from top to bottom
to fill one tagari at a time. Tagari after tagari is poured in rows on
the other undisturbed half to make a layer which is then sprinkled with
water. This is repeated until one-half of the contents of the pit is
doubled lengthwise over the other. The heap is then watered, suflicient
being added at this first turn to prevent the wasteful use of water
afterwards. After turning, the heap should not rise more than twelve
inches above ground level. The second watering, 1.5 tins, is given
twenty-four days after charge. At the first turn, the materials should
be arranged on the windward side of the pit to avoid the cooling of the
mass and also excessive drying. During the rains, when heaps are made,
it is not possible to double one-half of the heap over the other. The
material should then be completely turned and the heap re-made. The
heaps should be made as near as possible to each other.
Second turn. One month after charge (Plate IX). The water required is
about three tins. The material is cut vertically in two inch slices and
piled up with watering as before along the empty half of the pit. The
material should fall loosely, under each stroke of the spade and not in
lumps, so as to ensure copious aeration. The third and fourth waterings,
1.5 tins each, are given five and six weeks after charge.
Third turn. Two months after charge. About two tins of water are
necessary. A rectangular heap is made on the ground alongside the pit or
in the field not more than 10 ft. broad at the base, 9 ft. wide at the
top and 3.5 ft. high, the material being spaded and piled with watering
as before. When the heap is made in the field, all the water needed
should be added at the time of carting. The contents of several pits may
now be placed side by side to save space, to economize water and to
facilitate removal. The fifth and sixth waterings, 1.25 tins each, are
given nine and ten weeks after charge. For the first time during the
process, extra labour, namely three men and four women for six hours, is
required for each pit at the third turn. As the heap can be made either
in the factory or in the field, this additional labour can be debited to
the application of the humus to the land.
Three months after charge the manure is ready, when it should be applied
to the land. If kept in heaps longer than three months after charge,
nitrogen is certain to be lost. There is no great harm in putting the
manure on the land after two months if urgently required, especially
when the process has run for some time and everything is in full working
order.
TIME-TABLE OF OPERATIONS
The complete time-table of the manufacture of compost, which takes
ninety days, is given in Table V.
TABLE V
THE COMPLETE TIME-TABLE FOR ONE COMPOST PIT
Day Event
1 Charging begins.
6 Charging ends.
10 Fungus growth established.
12 First watering.
16/17 First turning, compost inoculated with bacteria from another pit
thirty-days old.
24 Second watering.
30/32 Second turning.
38 Third watering.
45 Fourth watering.
60 Third turning.
67 Fifth watering
75 Sixth watering
90 Removal to field.
OUTPUT
Fifty cart-loads of ripe compost per pair of oxen per annum can be made
from the plant residues available on any holding. The quantity can be
more than doubled when all the dung and urine earth are used, provided
of course sufficient vegetable refuse can be secured. Fifty to
seventy-five tins (200 to 300 gallons) of water, according to the
season, are sufficient to make one cart-load of finished compost. No
extra labour is required other than that usually employed in the
cattle-shed, namely two men and three women. These are sufficient for
the work connected with forty oxen and the preparation of 1,000 carts of
compost per annum.
The labour needed for the annual manufacture of 1OOO cart-loads of
compost has been reduced to a minimum by: (1) the provision of a water
supply; (2) the general design of the cattle-shed and compost factory
and (3) the detailed training of the labour force to carry out the work
quickly and without unnecessary fatigue. This aspect of the manufacture
of humus has been greatly assisted by the system of managing labour
adopted at the Institute (Appendix D).
During the year 1930, when 840 cart-loads of compost were prepared, a
careful record of the actual time spent on compost making by the labour
employed to look after the work cattle, was made. It was found that one
half of the time of this labour was spent on the care of the cattle and
one half on the making of compost. The The total wages debited to actual
compost making came to Rs 441.5, i.e. to 8.5 annas, or ninepence
halfpenny, per cart-load of finished material. During the present year,
1931, the output has increased and is expected to reach 1,000 cart-
loads. It is best to spread the compost on the land directly it becomes
ready, so as to facilitate the distribution of farm work throughout the
year.
MANURIAL VALUE OF INDORE COMPOST
One-cart load of Indore compost is equivalent, as regards nitrogen
content, to two cart-loads of ordinary farmyard manure. Properly made
compost has another great advantage over ordinary manure, namely its
fine powdery character which enables it to be uniformly incorporated
with the soil and to be rapidly converted into food materials for the
crop. Taking everything into consideration, Indore compost has about
three times the value of ordinary manure.
Chapter V
THE CHIEF FACTORS IN THE INDORE
PROCESS
The Indore process enables the Indian cultivator to transform his mixed
vegetable wastes into humus; in other words to become a chemical
manufacturer. The reactions involved are those which take place under
aerobic conditions during the natural decay of organic residues in the
soil. The object of the process is to bring these changes under strict
control and then to intensify them. A knowledge of the chemical
processes involved and of their relative importance is therefore
essential in applying the process to other conditions. These matters
form the subject of the present chapter.
THE CONTINUOUS SUPPLY OF MIXED VEGETABLE WASTES
A continuous supply of mixed vegetable wastes throughout the year, in a
proper state of division, is the chief factor in the process. The ideal
chemical composition of these materials should be such that, after the
bedding stage, the carbon-nitrogen ratio is in the neighbourhood of
33:1. The material should also be in such a physical condition that the
fungi and bacteria can obtain ready access to, and break down the
tissues without delay. The bark, which is the natural protection of the
celluloses and lignins against the inroads of fungi and bacteria, must
first be destroyed. This is the reason why all woody materials--such as
cotton-stalks, pigeon-pea stalks and sann hemp (Crotalaria juncea
L.)--are laid on the roads and crushed by the traffic into a fine state
of division before composting. Still more refractory residues like the
stumps of sugar-cane and millets, shavings, sawdust, waste paper and
packing materials, old gunny bags and similar substances, must either be
steeped in water for forty-eight hours or mixed with moist earth in a
pit for a few days before passing, in small quantities daily, into the
bedding.
The vegetable wastes which have been utilized at Indore for the last six
years are the following:--
Residues available in large quantities: Cotton stalks, sann hemp--either
as green plants reaped before the flowering stage or as dried stems of
the crop kept for seed, pigeon-pea stalks, sugar-cane trash, weeds,
fallen leaves.
Residues available in moderate quantities: Mixed dried grass, gram
stalks, wheat straw, uneaten and decayed silage, millet stalks damaged
by rain, residues of the safflower crop, ground-nut husks, ground-nut
stalks and leaves damaged by rain, sugar-cane and millet stumps.
Residues available in small quantities: Waste paper and packing
materials, shavings, sawdust, worn out gunny bags, old canvas, worn out
uniforms, old leather belting.
. . . . The raw materials available at Indore differ greatly in chemical
composition and particularly in the percentage of nitrogen. Many of
these wastes, such as cotton-stalks, the stems of sann hemp and of the
pigeon-pea, and cane trash are too low in nitrogen for rapid
composting. Others--such as green hemp, reaped just before flowering,
ground-nut residues and leguminous and other weeds--contain higher
percentages of nitrogen, a portion of which is certain to be lost during
the process if these materials are composted singly. A proper mixture of
the various materials available, so that the nitrogen content of the
mass throughout the year is kept uniform and sufficiently high, is the
first condition of success. For this reason it is necessary to collect
and stack the various residues in such a manner that a regular supply of
dry, mixed, vegetable wastes (as already stated with a carbon-nitrogen
ratio in the neighbourhood of 33:1 after the material has been used as
bedding) is available right through the year. This could only be
accomplished at Indore: (1) by cutting the cotton-stalks soon after
picking is over so as to secure the maximum number of leaves; (2) by
growing a large area of sann hemp, which contains when withered as much
as 2.3 per cent of nitrogen; and (3) by securing as much green weeds,
groundnut residues and fallen