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(The Soil and Health)
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Part III
The Problem of ManuringChapter 12
Origins and Scope of the ProblemThe great problem before agriculture the world over is how best to maintain in health and efficiency the huge human population which has resulted from the Industrial Revolution. As has already been pointed out, this development is based on the transfer of food from the regions which produce it to the manufacturing centres which consume it and which make no attempt to return their wastes to the land. This amounts to a perpetual subsidy paid by agriculture to industry and has resulted in the impoverishment of large areas of the earth's surface. A form of unconscious banditry has been in operation: the property of generations to come, in the shape of soil fertility, has been used not to benefit the human race as a whole, but to enrich a dishonest present. Such a system cannot last: the career of the prodigal must come to an end: a new civilization will have to be created, in which the various reserves in the earth's crust are regarded as a sacred trust and the food needed is obtained not by depleting the soil's capital, but by increasing the efficiency of the earth's green carpet. This involves the solution of the problem of manuring.
Why does the problem of manuring arise? What is the reason for our constant anxiety about the state of the soil? This preoccupation is as old as the art of agriculture. The problem occurs throughout the world, being recognized as a first consideration among all cultivating peoples. Its antiquity and its universal character are striking and must lead us to conclude that it is based on something of fundamental importance.
Briefly stated, the necessity for manuring arises out of our interference with the natural cycle of fertility. It is perhaps the most insistent of those problems which owe their origin to human action directed towards manipulating for the benefit of humanity the life of the vegetable and animal kingdoms. For be it admitted, the operations of cultivation, sowing, and reaping -- all the acts that make up agriculture -- are serious interruptions or interventions in the slow and intricate processes which make up growth and decay.
This is, perhaps, the place to devote a few words to this basic conception of agriculture as an interference with Nature. I have been attacked for not recognizing that interference. My constant references to Nature as the supreme farmer have been found inapplicable and inept, it being pointed out that if we were to follow Nature alone, we should be restricted to those small harvests which she is accustomed to provide, to the gatherings from the woodland and the hedgerow, from the wild pasture or the moor. I am accused of ignoring the fact that the whole aim of the cultivator is to do better than Nature and that the success attained in this direction is a source of legitimate pride.
It is, therefore, not out of place to take this opportunity of stating that the conception of agriculture as an interruption or interception of natural processes has always been recognized by me. (See especially what I wrote for students in a small book on Indian Agriculture, p. 11, which was published by the Oxford University Press in 1927.) Where I part company with my critics is in my general view of the unbalanced nature of these human acts. Intervention there must be: the most elementary act of harvesting is an interception: the acts of cultivation, sowing, and so forth are even more deliberate intrusions into the natural cycle. But these interruptions or intrusions must not be confined to mere exploitation: they involve definite duties to the land which are best summed up in the law of return: they must also realize the significance of the stupendous reserves on which the natural machine works and which must be faithfully maintained.
The first duty of the agriculturist must always be to understand that he is a part of Nature and cannot escape from his environment. He must therefore obey Nature's rules. Whatever intrusions he makes must be, so to say, in the spirit of these rules; they must on no account flout the underlying principles of natural law nor be in outrageous contradiction to the processes of Nature. To take a modern instance, the attempt to raise natural earth-borne crops on an exclusive diet of water and mineral dope -- the so-called science of hydroponics -- is science gone mad: it is an absurdity which has nothing in common with the ancient art of cultivation. I should be surprised if the equally unnatural modern practice of the artificial insemination of animals were not also to be condemned. Time will show.
But, provided that the actions of the cultivator are well conceived, that they have been proved successful by long experience, that they follow the essential course of Nature without real disobedience, that the character of the intervention undertaken is comprehended and that measures are initiated to restore the natural cycle in a proper way, much may be accomplished by man: and this is the art of agriculture.
The final proviso is of the utmost importance; we must give back where we take out; we must restore what we have seized; if we have stopped the Wheel of Life for a moment, we must set it spinning again.
Such a conception is very different from the all too prevalent idea which sees Nature as a parsimonious and very sparing provider of scanty, dispersed, and irregular harvests, a force which has to be stimulated by chemicals into adequate response, and controlled by the ingenuity and inventions of modern times. On this ingenuity and on those inventions rests, so it is claimed, the constantly growing food supply needed by modern populations, and much time is devoted to reckoning up the magnitude of this human achievement. The argument is based on figures of increased crop and animal production over the last few generations of human life and ignores the fact that these results depend on the plunder of the capital of the soil. The conclusions reached are fundamentally erroneous and are fraught with the certainty of failure and catastrophe.
This want of perspective and lack of humility dominates most of the short-term solutions of the problem of manuring, which from its very nature calls for the closest consideration of natural law. Without further ado I therefore propose to return to my usual method of first reflecting on the natural processes governing the question at issue, then examining what departures from these processes have been made by human action, and finally asking my readers for a sympathetic consideration of a certain point of view which may in some respects be new and even surprising.
The methods adopted by Nature for maintaining the earth's surface in fertility have been referred to throughout this book. They need only be briefly summed up here.
There is first a slow creation and interchange of soils by means of weathering and denudation through the agency of water or wind. Soils are constantly being shifted and redistributed. This long, slow process prevents the earth's soils from becoming static, in fact from becoming stale and worn out: we have only to imagine what would be the state of affairs as regards the supply of minerals if this process of natural regeneration did not take place. Secondly, there is a vertical movement whereby the roots of trees draw up the minerals of the subsoil, which then become distributed by the leaf fall. The constituents of the subsoil are thereby and by means of the earthworm continually being added to the top soil. There is thirdly the deposit on the surface of new organic residues everywhere on a colossal scale: these are derived from all vegetable growths -- trees, grass, or whatever they may be -- which are agents for catching and using the power of the sun, the final source of fertility. Fourthly, there are animal wastes, both the wastes from living creatures and the decomposition products of their dead bodies; these wastes in all their forms are in nature always widely dispersed. Finally, these factors of fertility are acted upon, one might almost say directed, by moisture and by air: they are first mechanically mixed and then transformed in their biological, physical, and chemical characters by the action of the smaller animals and invertebrates and by the agency of millions of microscopic fungi and bacteria.
Much of our interference with this complex of processes is unavoidable. The settlement of areas for cultivation is a first necessity: we cannot afford to have our farms moved hither and thither. The allocation of chosen crops for selected fields then follows. This is a very violent interference with natural life. which mixes and rarely selects. The consequences of this major interference are made good by systems of rotation and mixed crops, which are designed to restore that variety of vegetable growths which had to be sacrificed for purposes of convenient cultivation: the old device of fallowing is part of the rotation principle. That this restoration of fertility is often very imperfect has already been shown in the chapter on The Maintenance of Soil Fertility in Great Britain.
Apart from these long-term intrusions there are, especially in Western agriculture and in a great deal of plantation agriculture, short-term omissions -- annual, seasonal, and indeed daily -- to maintain the fertility cycle. These omissions are mostly unconscious and are, therefore, not being made good by counter-measures: herein lies their danger. There is, first, the general neglect of vegetable wastes: these are not faithfully returned to the fields as they should be: they are sometimes burnt, and they are partly removed for industrial and other purposes and then buried for decades in sealed tips of urban refuse. Far more injurious is the neglect of animal wastes. Human wastes are washed away, while the wastes of domestic animals, often insufficient in volume, are concentrated in rank manure heaps instead of being dispersed. This matter of the dispersal of animal wastes is important.
The effect of these interferences with natural law accumulate and the discussion of the problem might be prolonged on these lines. But the reader has already been put in possession of the gist of the subject; in order not to deflect his attention the remainder of this section of the book will be devoted to special points which seem at the present stage to throw the most light on the vital problem of manuring.The Phosphate Problem and its Solution
The problem of manuring does not concern the top soil only: it includes the subsoil. The circulation of minerals between soil and subsoil is an essential factor in any manurial programme.
As already stated, the past history of our fields has constituted one of those major intrusions into the natural fertility cycle of which the results are now becoming apparent. Most of these fields were originally under forest. This forest cover would soon be re-created if our arable or pasture land were enclosed and left to itself. This is Nature's time-honoured method of restoring soil fertility. The trees and undergrowth soon accumulate the essential stores of humus; the roots break up the subsoil in all directions and comb it thoroughly for minerals like phosphates, potash, and the various trace elements, which are then converted into the organic phase in the leaves and afterwards transformed into humus for feeding the soil population. At the same time, the roots leave behind them not only a pulverized subsoil, but also numerous channels for air and water, as well as a supply of organic matter. In this way the roots improve the condition of the subsoil; permeability is restored; and, what is equally important, the natural circulation of minerals between subsoil and soil is renewed. Everyone knows how fertile are the soils left by the forest. One reason is that they are rarely short of minerals. The ultimate source of minerals such as phosphates is the primary or igneous rocks, many of which contain appreciable quantities of phosphate in the form of apatite. From these primary rocks the sedimentary rocks are derived. Both classes give rise to subsoils and soils, so that when we look at the phosphate and indeed the mineral question as a whole and start our studies at the source, we should expect any shortages of phosphate or other minerals to be due to some error in soil management. This is exactly what has happened. In the course of years of cultivation the circulation of minerals between subsoil and soil has deteriorated. The constant treading of animals, the passage of cultivating machines, the failure to use afforestation to renew soil fertility, the failure to replace the root system of the trees by those of deep-rooting plants while the land is rested under grass, and the excessive use of chemicals have caused the subsoil to form a definite pan which restricts the passage of roots, interferes with the aeration of the lower layers, and leads to a poor circulation of minerals between the surface soil and the great reservoir of the subsoil. Crops have in this way been forced to live more and more on the thin upper layer of cultivated soil and so have exhausted such elements as phosphorus, potassium, and the trace elements. The soil, therefore, suffers very much as an animal does when the circulation of the blood is defective. The first matter to attend to, therefore, is to restore the natural circulation of phosphate and other minerals between subsoil and soil. At the same time we set in motion, through the operations of weathering and denudation, the natural replenishment -- from the underlying rocks -- of the minerals removed by crops and livestock.
(In all future afforestation schemes care should be taken to use the forest to improve the areas under agricultural crops. This can most easily be done (1) by starting the new plantations on land which has been subsoiled and brought into good condition by suitable cultivation, temporary leys and by abundant humus, (2) by raising the young trees in humus-filled nurseries so that the mycorrhizal association can be established from the beginning. and (3) by a suitable mixture of trees. In this way the time taken to grow marketable timber could be vastly reduced and the income of the new plantations increased. As soon as possible these afforested areas should be cleared and then given back to agriculture. Another area could then be put under this long term forestry rotation. In this way forestry can be used to restore the fertility of the soil as well as to provide timber. The marriage of forestry and farming must be included in all our future agricultural policies.)
Some fifty years ago during my student days spectacular results were beginning to be obtained when heavy land under grass was dressed with finely pulverized basic slag. Basic slag is the name given to the used-up limestone lining of the Bessemer converter, by which the phosphorus from certain types of iron ore is removed. The molten metal gives up its phosphorus to the limestone with the formation of one of the phosphates of calcium. This, when finely powdered, acts as a phosphatic manure. In this way a new artificial manure was added to an already long list.
The obvious effect of this slag on a piece of heavy land under grass is to improve the herbage, the clovers in particular. But when basic slag is added to pastures on light, permeable land and to grass on the chalk, negative results are often obtained. I well remember how all this troubled me when I connected these results with my knowledge of geology and of the microscopic structure of the primary rocks. Something seemed to be wrong somewhere. I put my doubts to my instructors and suggested that the whole phosphate question should be reopened. Their explanations failed to satisfy me. Then about 1904 at the Royal Agricultural Show at Park Royal a chance observation led, some forty years later, to the practical solution of the phosphate problem. Some turves taken from the plots of the Cockle Park experiments were included in one of the exhibits dealing with agricultural research. One of these turves was taken from the plot which had received basic slag, the one alongside from the control plot. The difference in the herbage was amazing, but what also interested me was the deep, black layer of humus under the slagged turf and the absence of a similar humus layer in the control. Thirty-four years later, in 1938, I was able to continue this phosphate story. I discussed my observations with the late Sir Bernard Greenwell and suggested that basic slag must act indirectly by improving the aeration of heavy soils, whereby the vegetable and animal wastes are converted into humus, which in turn would improve the grasses and clovers. I pointed out that under the turf of heavy, close grassland nitrates were always in defect and that the provision of more oxygen invariably improved matters. He at once proceeded to use a subsoiler, drawn by a caterpillar tractor, four feet apart and twelve to fourteen inches deep, on his grassland on the London clay and immediately obtained results comparable with those obtained by an average dressing of slag. The passage of the shoe of this machine acted like a mild explosive and shattered the subsoil. The land, of course, must be in the right condition to obtain the maximum effect -- it must not be too wet or the pan will not shatter.
Sir Bernard's death in 1939 and the present war put an end to the work in progress at Marden Park. The results thus so far obtained, however, were set out in 1940 in Chapter VII of An Agricultural Testament in the hope that some pioneer would be sufficiently interested to continue this phosphate inquiry. In 1943 the expected happened. I received a letter from a correspondent in Sussex -- Mr. R. Delgado, Little Oreham, near Henfield -- to the effect that he had prevailed on his local War Agricultural Executive Committee to subsoil one of his pastures. At the same time a neighbour applied ten hundredweight of basic slag to each acre of similar land. In view of the importance of this work, the correspondence is here quoted in extenso.
The first report is dated 27th November 1943:
"After reading Sir Albert Howard's Agricultural Testament and the account he gives in it relating to the work of the late Sir Bernard Greenwell with the use of a subsoiler on pastures overlying clay, it was decided at once to contact the local W.A.E.C. with a view to finding out the name of a contractor who possessed the necessary tackle to carry out such work on my farm.
"The local Committee wrote back to say that I was misinformed and that the only use a subsoiler had was on arable ground behind a plough. After a further exchange of letters they agreed to send a crawler tractor and a wheel-type Ransomes subsoiler.
"A further argument ensued as to the depth and distance apart, but, after the subsoiler had been up and down the field once, I pointed out to the officer that no effective shattering of the subsoil could take place further than two feet on either side of the share, and he eventually came down to doing them six feet apart and fifteen inches deep.
"Had the work been carried out strictly in accordance with Sir Bernard's stipulation, I am certain that the eventual results would have been better. However, the response from the worst field on this farm was encouraging. When the work was completed, it was stocked with yearling and bulling heifers and three horses. There was not much grass on the field to start with, so good and bad hay were fed to supplement the grazing. The good hay was, naturally consumed and the bad was dunged and trodden on to form compost in situ. The field was finally shut up in July absolutely bare, four months after subsoiling.
"Despite the absence of rain in this part of the country during the summer, the flora on this meadow had changed to an emerald green on shutting up and has remained so ever since.
"On November 20th I went to look at it and was agreeably surprised to observe many worm casts which had hitherto been absent. The milking herd was turned into it the following day. Their relish for the short bite was very noticeable, particularly where the worm casts were more numerous, and the milk yield went up.
"In the autumn of last year a friend, farming nearby on the same type of soil, dressed a meadow with ten hundredweight of slag to the acre. I was privileged to see it this June, closely grazed and a very good colour. Everyone is aware of the virtues of slag on clay soils.
"In July, just before shutting up the field described above, my friend paid me a visit and we were standing in this field having a look at my young stock when she remarked on the greenness of my turf, complaining sorrowfully that her slagged meadow was brown, scorched, and devoid of any feed.
"It would be as well to state here that the flora in my particular meadow was that which is found in pastures which tumbled down to grass after the last war with a proportion of volunteer clover and a semi-swamp variety of weeds, whereas in my friend's I had seen a preconceived mixture of grasses and clovers. And in order to complete the treatment of my meadow, after a pulse crop has been taken, it will be sown down to deep rooters and Leguminosae.
"There remains the cost of the work. Subsoiling by contract with the W.A.E.C. under the mole-draining scheme, inclusive of piped outfalls averaging three to each four acres and inclusive of a 50 per cent grant, came to a little over 25s. per acre. Subsoiling, as recommended by Sir Bernard Greenwell with one's own power and tackle, one could probably carry out to-day for a maximum of 5s. per acre.
"The cost of slag, which is either £6 per ton or £3 10s., I am not sure which, would work out on a dressing of ten hundredweight to the acre at the lowest at 35s. per acre exclusive of labour.
"Though admitting that slag is better than nothing in that humus formation under the turf sets in after a suitable application, apart from the relative merit of costs I am of the opinion that one can obviate any unknown chemical reaction in the soil by seeking the same, if not possibly better, results by the use of the subsoiler. Unfortunately I have not as yet been able to go and see the slagged meadow this autumn to discover what verdict is given by the earthworm.
"It might be of interest to add that fungi in the shape of mushrooms, only very sparsely scattered in my meadow last year, abounded in great numbers this autumn, whereas it is well known that slag will do away with them for evermore."
The matter was followed up further and in a subsequent report dated 3rd April 1944 Mr. Delgado continues the story of his interesting experiment:
"In April 1943 I subsoiled a four-acre meadow which was literally soused with a century or more of organic decay for about four inches under the turf. I should imagine it was very acid since it hardly grew any hay and the stock loathed it. It was, in fact, one of those meadows which give spectacular results with a heavy dressing of slag. In the previous autumn stock had been shut up in it and fed with green stuff carted from another field.
"Soon after subsoiling, the meadow was ploughed and one-third of it dressed with ten hundredweight of slag to the acre. It was sown with oats and tares. The crop was uniform throughout the field. In the autumn of 1943 the field was ploughed again. The ploughman, who did not know I had slagged a portion of the field, noticed the land was harder on the slagged area. Winter oats were drilled and at the time of writing (3rd April 1944) the crop is uniform.
"The oats are going to be undersown with a grass mixture, and it will be interesting to see if there is any difference in the take of the seeds as phosphates are supposed to be essential when laying down to grass."
In a further letter dated 22nd April 1944 Mr. Delgado stated that as the oats were very forward he had been compelled to graze them by cattle. The stock grazed the oats evenly and showed no preference whatsoever for the slagged portion. He will continue to keep this field under careful observation and report if any differences develop, and also take note of the reaction of the grazing animal to the following grass crop.
On 20th October 1944 Mr. Delgado reported that the oat crop was uniform and yielded about thirty hundredweight of grain to the acre. The take of the clovers and grasses in the seeds mixture was absolutely uniform all over the field which was evenly grazed by the livestock. As far as could be seen up to the time of writing the application of slag at the rate of ten hundredweight to the acre to a portion of this subsoiled field produced no result.
There seems no doubt that the effect of basic slag is mainly to promote the formation of humus under the turf of heavy land under grass by improved aeration and that similar results can be obtained at much less cost by means of the subsoiler. ("Is Basic Slag Really Necessary?", News-Letter on Compost, Nos. 8 and 9, February and June 1944.)
Mr. Friend Sykes has obtained equally striking subsoiling results on arable land. This he has done by breaking up the pan under the plough sole. His experiences are described in detail in Appendix D to this book.
Clearly the moment peace comes and a supply of implements becomes available a regular subsoiling campaign will have to be set in motion throughout the length and breadth of Great Britain. Indeed, in most parts of the world, systematic subsoiling is certain to be one of the great advances in agriculture. Captain Moubray has already obtained good results in the Mazoe valley in Southern Rhodesia. Some striking effects of subsoiling have also been obtained on Mr. Franklin Roosevelt's home farm in the United States of America. Subsoiling is certain to prove the first great step in maintaining the mineral supplies of the surface soil and so rendering obsolete many of our ideas on manuring. It sweeps current advice on phosphate manuring into the lumber room of exploded ideas. It may also prove to be of great value in the reclamation of alkali land.
Not only does subsoiling open the door to the reform of arable farming, but it will, above all, be a practical solution of some of the problems of our temporary and permanent grassland. Without realizing it, we have in the course of long processes of cultivation allowed our fields and pastures to become pot-bound: this condition puts at least half of the fertility cycle out of action. By correcting this condition and allowing air to penetrate beneath the surface down to and into the subsoil, we restore that natural supply of oxygen without which humus formation cannot properly proceed. Subsoiling, in fact, is the parallel process to drainage and perhaps, because so long neglected, is even more important: the one process controls the surplus water of the soil and the other guides and restores the supply of air. The soil like the compost heap needs both air and water at the same time.
In this way only can we make a full use of the earth's green carpet, and it is only by the agency of the green carpet that we are able to trap the sunlight: in proportion as this green carpet is not utilized we lose that much solar energy. The practical effects of the change are indicated in the reports quoted above. It is certain that by this reform carried out all over the country the stock-carrying capacity of our grass areas will go up by leaps and bounds. The door will then be opened to making full use of the improved varieties of grasses, clovers, and herbs -- which must always include deep-rooting types and which must also have ample leaf area for intercepting the sunlight -- needed by the ruminant stomach. We shall also be able to take in hand all our hitherto neglected second and third classes of land. Most of these will go up at least a class after they have been treated by methods similar to those which Mr. Sykes and Mr. Delgado have so successfully applied at Chantry and at Little Oreham. The great openings are certain to lie in these and even in fourth-rate areas. We have only just begun to deal with the hill farms -- those cradles of the breeds of livestock of to-morrow. England need no longer contract her real farming to the best land as she is doing now.The Reform of the Manure Heap
Subsoiling will solve the mineral side of manuring. The reform of the manure heap and the full use of sheet-composting are the roads by which the nitrogen problem must be approached.
If the soil is a living thing, as we have continually been insisting in this book, so also in an even more intense way is the manure heap. Such a manure as compost is simply a teeming mass of microbial and fungous life. This life, like all life, never stands still; it has its own cycles and is in a very different state at different times.
All cultivators like their farmyard manure well rotted. A hot manure, i.e. a fresh manure, cannot safely be introduced into a worn-out soil which is then to grow a crop. This universally accepted piece of practice is a first recognition of the potentially dangerous nature of the traditional heap of farmyard manure -- evil-looking, evil-smelling, full of maggots, and the paradise of breeding flies. Our extraordinary habit of heaping up animal excrement together in these insanitary masses is, it is true, established among us by age-old tradition. That must not prevent us from probing into the practice and questioning it.
It is not natural. Nature does not collect the excrement of her fauna in this way. Their droppings in a wild pasture are most widely scattered by the roaming habits of the animals, far more widely than they are even in a field grazed by domesticated beasts. The admitted distaste of such grazing animals for feeding off patches of grass which have been stained, as it is called, by their own wastes some time previously should alone have given us a hint. Horses, for instance, are most particular and may be classed as most cleanly beasts. Nowhere in Nature (if we except a few sea-bird habitats where suitable nesting areas are restricted) do we find the noisome nuisance of the manure heap.
The fact is that by collecting farmyard manure in this way and leaving it, sometimes for many months, at least three deleterious processes are induced.
In the first place, the rain washes out an untold portion of the valuable elements: this is finally lost to the farmer. Whoever has seen the richest part of a large manure heap leaching away into a ditch without hope of recovery may well ask himself why the farmer was at so much trouble to gather together what he is so eager to lose again. The rich exudation, which leaves the heap, is like an opened artery: all goodness drains away: a less valuable mass of stuff is left, impoverished of much of the best constituents. Yet this sort of carelessness is met with in almost every farming community outside China, and what is much worse is looked on as nothing in the least abnormal.
In the second place, there is a considerable loss of nitrogen to the air due to the establishment of an anaerobic flora. Though not so obvious as leaching by rain, yet much loss of the valuable element -- combined nitrogen -- occurs. Such losses are a foregone conclusion if we remember that, as we pointed out above, farmyard manure is not a static substance. Its very nature implies change, just because it is alive. The natural changes it would undergo if left alone would be to become humus by incorporation after fermentation with ample vegetable wastes. But, if not thus left to its natural destiny, if heaped up into a huge solid mound by man's agency, it does not on that account wholly cease to live: and among the living changes which it is bound to undergo is the release of the excess nitrogen by denitrification so that a mixture suitable for humus formation remains. The combined nitrogen it contains, which is so valuable a plant food element and for which the surrounding vegetation is crying out, escapes into the air either in the form of ammonia -- the characteristic smell of which hovers over every manure heap -- or as free nitrogen gas.
In the third place, something far worse than leaching and the escape of nitrogen is apt to take place in the manure as a final result of cutting off the air supply. Decay in the forms which we have been investigating is one of the ways in which Nature turns her Wheel. It is not, however, her only or exclusive process. There are processes, commonly known as the putrefactive processes, which she also employs in certain circumstances. These processes are always induced when there is insufficient oxygen. In the absence of oxygen -- the great purifying agent which by combining burns up the elements present in decaying bodies -- these putrefactive processes form a special type of compound usually accompanied by the generation of noxious gases. This is putrefaction and we all know, by common experience, what that word means. It is Nature's method of removing wastes which for some reason she is unable to deal with normally by what we may call her methods of healthy decay. Perhaps because there is some stoppage, some kink, in her normal processes, she carries out these alternative putrefactive changes in an unpleasant and sensational way. The sights and smells of putrefaction are highly disagreeable to the higher living creatures, man not excluded. If we like to use a poetical image, it is Nature thwarted, and in wrath.
Now in a manure heap these putrefactive processes are apt to take the place of the normal decay processes, especially when manure is heaped on a concrete floor or in a concreted pit. Any farmer who wishes to observe these putrefactive processes can easily do so by assembling two manure heaps side by side, one on freshly broken-up earth, the other on a concrete floor. The air supply of these two heaps is very different. The first obtains a fair supply of oxygen: in the second aeration is restricted and putrefactive changes, accompanied by an offensive odour, soon set in. Incidentally this simple experiment establishes the principle that the earth itself breathes provided the surface soil is kept open. This is one of the reasons why we must always cultivate.
If putrefactive processes have begun, then the manure is not at a stage suitable for plant food. It will have to undergo some very prolonged changes before the plant can get much benefit from it. Whereas decomposition without putrefaction is the principle of compost-making, putrefaction delaying and complicating the normal absorption of food needed by soil and plant is what often follows from the nuisance of the manure heap. The reason is simple. The mere mechanical heaping up of the animal excrement into one large mound has deprived that excrement, first, of the oxygen it needs for burning up, and second, of that juxtaposition and mingling with sufficient waste vegetation of the soil which goes to make normal decay. We have produced the conditions needed by an anaerobic flora. This always means loss. We have not mixed the vegetable and animal wastes in the proportions Nature has ordained.
We thus always return to the same point: animal and vegetable must he mixed in correct proportions in their death, as in their life, processes.
This criticism of a very ancient practice in agriculture will appear bold. The manure heap has been used by generations of farmers. If there were nothing else, we should have to go on accepting it. Even this should not blind us to its disadvantages. When thirty years ago I first began to look round for an alternative method of collecting manurial material, the simple reason was not the disadvantages mentioned, but that there did not appear to me to be enough manure available to the Indian peasant on whose behalf I was working. The national habit of burning the cow-dung as fuel severely limited what could be put on the fields, and I became convinced that some method of eking out his scanty supplies was essential if he was to take advantage of the advances in plant breeding which the agricultural research workers of India were making: otherwise our work would be stultified. It was natural to study the successful methods in use in another part of the East and to consider the ideas underlying the Chinese practice of increasing the volume of fertilizing material by composting animal and vegetable wastes together. It quickly became part of my own routine to compost all the wastes of my experimental areas. The practical results soon forced themselves on my attention, but only in the course of time did the full meaning of the Chinese principles become clear to me.
In the end the substitution of the compost heap for the manure heap in my work proved to have been the most significant step in my education as a scientific investigator.Sheet-composting and Nitrogen Fixation
Subsoiling and the reform of the manure heap are the first steps in the solution of the problem of manuring. These will enable the soil to make a further supply of humus by a third method -- sheet-composting. The fourth and last step naturally follows -- the encouragement of the non-symbiotic soil organisms like Azotobacter, which fix atmospheric nitrogen.
Once the surface soil has been improved by the circulation of minerals and the supply of humus, the land will be in a condition to begin to manure itself by the process of sheet-composting. By this is meant the automatic manufacture of humus in the upper layers of the soil. Naturally the raw materials for this must first be provided. These are: (1) vegetable residues in the shape of the stubble and roots of crops like cereals; (2) temporary leys due for ploughing up, which must always include deep-rooting plants and herbs; and (3) green-manures, catch crops, and weeds.
For humus of the first quality to be made quickly from these three classes of vegetable matter we must always provide a supply of animal residues, either in the form of the droppings of animals or of reformed farmyard manure (compost). Besides this activating material we need oxygen, moisture, and warmth. If the land is properly farmed, we do not require a base to neutralize acidity: the soil will arrange this matter for us. Oxygen, of course, comes from the atmosphere and costs nothing: the moisture is provided by the soil, by rain, and by dew: the necessary warmth is available if we begin sheet-composting before the land begins to cool in the late summer and early autumn.
The best results will always be obtained with sheet-composting when the stubbles, temporary leys, green-manures, catch crops, and weeds are only lightly covered with earth. A deep covering of soil must be avoided, as sheet-composting requires a copious supply of air. The fermenting layer only needs just sufficient soil to keep the mass moist. When stubbles have to be converted into humus, the supply of moisture can be enhanced by composting and lightly burying as soon as possible after reaping and before the surface soil has time to dry out. There is nothing to prevent this operation following the binder once the sheaves are set up in rows, leaving narrow untreated strips between the cultivated areas.
Provided the soil is in good heart, a second composting is possible by sowing a catch crop on the sheet-composted land. Such land will do two things at the same time -- prepare compost, and grow a catch crop. These catch crops can either be eaten by stock or disced in before winter comes. The object of all this is to make the fullest use of solar energy by always having the soil in the late summer or autumn under a crop of some kind or, failing a crop, under weeds. Vegetable matter must always be made and then converted into humus for the following year.
Proceeding in this manner a useful supply of humus will be created and ready for nitrification for the next year's crop. Further, all nitrates formed in the soil during the late summer and early autumn, which otherwise would be lost by leaching or denitrification, are immobilized and carried forward safely to the next crop.
Everything now will be ready for the last item needed in the solution of the nitrogen problem -- nitrogen fixation. The organisms which carry this out must be provided not only with organic matter -- to supply energy and food -- but also oxygen, moisture, and a sufficient supply of base such as calcium carbonate to prevent an acid condition of the soil developing. It is more than probable that the good results which often follow dressings of chalk or powdered limestone are due in large part to nitrogen fixation.
Such fixation also takes place in a properly made compost heap; it must be continued in the soil; this is, however, only possible in really well farmed land.
The view that we must make every use of natural means -- such as subsoiling, the full utilization of animal and vegetable wastes, sheet- composting, and nitrogen fixation -- before even thinking of spending money on chemicals needs no argument. It will, I think, be found that when we make the fullest use of all these methods and follow the teachings of Mother Earth, we shall find it difficult to escape the conclusion that Nature, after all, is the supreme farmer.The Utilization of Town Wastes
The zones of agricultural land round our towns and cities are largely used to produce the fresh vegetables, fruit, and milk needed by the population. These areas ought, therefore, to be maintained in the highest possible condition. For this large volumes of compost will be needed. How is this to be obtained in areas where the supply both of vegetable waste and of activators of animal origin are certain to be small? The answer is: By the conversion into humus of the wastes of the towns themselves supplemented by baled straw brought in from outside.
Although our towns are fed from the countryside, little or no return of urban wastes to the land takes place. The towns are, therefore, parasitic on the country. This will have to stop. The wastes of these areas must go back to the soil. This can easily be accomplished by large-scale humus manufacture on the part of the municipalities. Instead of allowing the dustbin refuse to be buried in controlled tips or burnt in incinerators, this material should be turned into compost by the help of the crude sewage from the mains.
Two methods of using crude sewage as an activator are possible. We can either use it direct or filter it and then convert the sludge into powder, at the same time rendering the filtrate innocuous by chlorination. Both this dried sludge and crude sewage are excellent substitutes for animal activators. A small amount of dried sludge -- about 1 per cent of the dry weight of the vegetable matter used -- is sufficient to activate vegetable wastes. This powder will provide the owners of urban gardens and allotments with an excellent substitute for the animal manure now so difficult to obtain. The use of crude sewage is also practicable: long shallow pits may be filled with several layers of baled straw and dustbin refuse, which can then readily be moistened and activated by the sewage without the least nuisance and converted into excellent compost in some three months.
To get all this under way in this country successful examples must first be provided to overcome the well-known inertia of our municipalities. Some are already in existence. In South Africa a nation-wide organization for converting the wastes of their towns and cities is in operation, as will be seen from the account contributed by Mr. J. P. J. van Vuren, the Co-ordinating Officer for Municipal Compost Schemes, in Appendix C. The preparation of dried sewage sludge is described in an article by Dr. Lionel J. Picton, O.B.E., in the News-Letter on Compost, No. 10, October 1944. On page 224 there is a description of a method of converting straw into compost by means of crude sewage only.
Fortified by successful examples elsewhere and stimulated by the already growing demand for properly made humus, it is only a question of time before our municipalities take up the preparation and sale of high quality compost and show how the town can make some return to the soil to which it owes its life.Summary
- The manurial problem can best be solved by copying the methods of Nature.
- The circulation of minerals between subsoil and soil must be restored by means of afforestation and the subsoiler followed by the use of deep rooting plants in the temporary ley.
- The nitrogen problem can be solved by: (a) the reform of the manure heap; (b) by the sheet-composting of stubbles, green-manures, catch crops, and weeds; (c) by assisting the fixation of atmospheric nitrogen.
- An ample supply of compost in the neighbourhood of towns and cities can be provided by introducing municipal composting on the lines now in successful operation in South Africa.
Next: 13. The Indore Process and Its Reception by the Farming and Gardening Worlds
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