Small
farms
An Agricultural Testament

by Sir Albert Howard

Chapter V
Practical Applications of the Indore Process

AFTER the first complete account of the Indore Process was published in 1931, the adoption of the method at a number of centres followed very quickly. The first results were summarized in a lecture which appeared in the issue of the Journal of the Royal Society of Arts of December 8th, 1933. About 2,000 extra copies of this lecture were printed and distributed during the next two years. By the end of 1935 it became evident that the method was making very rapid headway all over the world: an increasing stream of interesting results were reported. These were described in a second lecture on November 13th, 1935, which was printed in the Journal of the Society of November 22nd, 1935. This lecture was then republished in pamphlet form. In all 6,425 extra copies of this second lecture have been distributed. During 1936 still further progress was made, a brief account of which appeared in the Journal of the Royal Society of Arts of December 18th, 1936; 7,500 copies being printed. Two translations of the 1935 lecture have been published. The first in German in Der Tropenpflanzer of February 1936, the second in Spanish in the Revista del Instituto de Defensa del Café de Costa Rica of March 1937.

These papers did much to make the Indore Process known all over the world and to start a number of new and active composting centres. The position, as reached by July 1938, was briefly sketched in a paper which was published in the Journal of the Ministry of Agriculture of Great Britain of August 1938.

In this and succeeding chapters an attempt will be made to sum up progress to the time of going to press. It will be convenient in the first place to arrange this information under crops.

Coffee

The first centre in Africa to take up the process was the Kingatori Estate near Kyambu, a few miles from Nairobi, where work began in February 1933. By the purest accident I saw the first beginnings of composting at this estate. This occurred in the course of a tour round Africa which included a visit to the Great Rift Valley. As I was about to start from Nairobi on this expedition, Major Belcher, the Manager of Kingatori, called upon me and said that he had just been instructed by Major Grogan, the proprietor of the Estate, to start the Indore Process and to convert all possible wastes into humus. He asked me to help him and to discuss various practical details on the spot. I gave up the tour to the Great Rift Valley and spent the day on the Kingatori Estate instead, where it was obvious from the general condition of the bushes and the texture of the soil that a continuous supply of freshly made humus would transform this estate, which I was told was representative of the coffee industry near Nairobi. In a letter dated September 19th, 1933, Major Belcher reported his first results as follows:

Two years later he sent me a second report in which he stated that during the last 28 months 1,660 tons of compost, containing, about 1.5 per cent. of nitrogen, had been manufactured on this estate and applied to the land. The cost per ton was 4s. 4d. -- chiefly the expense involved in collecting raw material. The work in progress had been shown to a constant stream of visitors from other parts of Kenya, the Rhodesias, Uganda, Tanganyika, and the Belgian Congo. Major Belcher has lost count of the actual numbers.

This pioneering work has done much more than weld the Indore Process into the routine work of the estate. It has served the purpose of an experiment station and a demonstration area for the coffee industry throughout the world. Many new centres followed Kingatori. The rapid spread of the method is summed up by Major Grogan in a letter dated Nairobi, May 15th, 1935, as follows:

Major Grogan in referring to the spread of the Indore Process in East Africa, has omitted one very material factor, namely, his personal share in this result. He initiated the earliest trial on the Kingatori Estate and has always insisted on the method having a square deal in Kenya. In Tanganyika the influence of Sir Milsom Rees, G.C.V.O., has led to similar results.

This example of the introduction and spread of the Indore Process on the coffee estates of Kenya and Tanganyika has been given in detail for three reasons: (1) it was one of the earliest applications of the Indore method to the plantation industries; (2) it is typical of many other similar applications elsewhere; and (3) it first suggested to me a new field of work during retirement in which the research experience of a lifetime could be fully utilized.

Kenya and Tanganyika are only two of the coffee centres of the world. The largest producer is the New World. Here satisfactory progress has been made following the publication in the West India Committee Circular of April 23rd, 1936, of a short account of the Indore Process. This led to important developments, first in Costa Rica and then in Central and South America, as a result of a Spanish translation by Senor Don Mariano Montealegre of my 1935 lecture to the Royal Society of Arts to which reference has already been made. This was widely read in all parts of Latin America: the lecture drew attention to the vital necessity of organic matter in the production of coffee in the New World. During the next two years no less than seven Spanish translations of my papers on humus were published in the Revista del Instituto de Defensa del Café de Costa Rica. In January 1939 a special issue of the Revista entitled En Busca del Humus (In Quest of Humus) appeared. This was devoted to a collection of papers describing the Indore Process and the various developments of the last eight years.

The marked response of coffee to humus in Africa, India, and the New World suggested that the crop would prove to be a mycorrhiza-former. A number of samples of the surface roots of coffee plants were duly collected in Travancore, Tanganyika, and Costa Rica and sent home for examination. In all cases they showed the mycorrhizal association.

Tea

The East African results with coffee naturally suggested that something should be done with regard to tea -- a highly organized plantation industry with the majority of the estates arranged in large groups, controlled by a small London Directorate largely recruited from the industry itself. The problem was how best to approach such an organization. In 1934 my knowledge of tea and of the tea industry was of the slightest: I had never grown a tea plant, let alone managed a tea plantation. I had only visited two tea estates, one near Nuwara Eliya in Ceylon in 1908 and the other near Dehra Dun in 1918. I had, however, kept in touch with the research work on tea. While I was debating this question Providence came to my assistance in the shape of a request from a mutual friend to help Dr. C. R. Harler (who had just been retrenched when the Tocklai Research Station, maintained by the Indian Tea Association, was reorganized in 1933) to find a new and better opening, if possible one with more scope for independent and original work. I renewed my acquaintance with Dr. Harler and suggested he should take up the conversion into humus of the waste products of tea estates. He was very interested and shortly afterwards (August 1933) accepted the post of Scientific Officer to the Kanan Devan Hills Produce Co. in the High Range, Tray encore, which was offered him by Messrs. James Finlay & Co., Ltd. On taking up his duties in this well-managed and highly efficient undertaking, Dr. Harler secured the active interest of the then General Manager, Mr. T. Wallace, and set to work to try out the Indore Process on an estate scale at his headquarters at Nullatanni, near Munnar. No difficulties were met with in working the method: ample supplies of vegetable wastes and cattle manure were available: the local labour took to the work and the Estate Managers soon became enthusiastic.

On receipt of this information I made inquiries from Dr. H. H. Mann, a former Chief Scientific Officer of the Indian Tea Association, as to whether the live wires among the London Directorate of the tea industry included anybody likely to be particularly interested in the humus question.

I was advised to see Mr. James Insch, one of the Managing Directors of Messrs. Walter Duncan & Co. At Mr. Insch's request an illustrated paper of instructions for the use of the Managers of the Duncan Group was drawn up in October 1934 and 250 copies were printed. The Directors of other groups of tea estates soon began to consider the Indore Process and 4,000 further copies of the paper of instructions were distributed. By the end of 1934 fifty-three estates of the Duncan Group in Sylhet, Cachar, the Assam Valley, the Dooars, Terai, and the Darjeeling District had made and distributed sample lots of humus, about 2,000 tons in all. At the time of writing, December 1939, the estates of the Duncan Group alone expect to make over 150,000 tons of humus a year. Similar developments have occurred in a number of other groups notably on the estates controlled by Messrs. James Finlay & Co., who have never lost the lead in manufacturing humus which naturally followed from the pioneering work done by Dr. Harler in Travancore. A good beginning has been made. The two strongest groups of tea estates in the East have become compost-minded.

It is exceedingly difficult to say exactly how much humus is being made at the present time on the tea estates of the British Empire. It is possible only to give a very approximate figure. In April 1938 Messrs. Masefield and Insch stated: 'It is probably no exaggeration to say that to-day a million tons of compost are being made annually on the tea estates of India and Ceylon, and this has been accomplished within a period of 5 years.' Since this was written the tea estates of Nyasaland and Kenya have also taken up the Indore Process with marked success.

These developments have been accompanied by a considerable amount of discussion. Two views have been and are still being held on the best way of manuring tea. One school of thought, which includes the tea research institutes, considers that as the yield of leaf is directly influenced by the supply of combined nitrogen in the soil, the problem of soil fertility is so simple as to reduce itself to the use of the cheapest form of artificial manure -- in this case sulphate of ammonia. This view is naturally vigorously supported by the artificial manure interests. The results obtained with sulphate of ammonia on small plots at Tocklai and Borbhetta are triumphantly brought forward to clinch the argument which amounts to this: that tea can be grown on a conveyor-belt lubricated by chemical fertilizers. The weaknesses of such an argument are obvious. These small plots do not represent anything in the tea industry: they only represent themselves. It is impossible to run a small plot or to manufacture and sell its produce as a teagarden is conducted. In other words the small plot is not practical politics. Again, land like Tocklai and Borbhetta which responds so markedly to sulphate of ammonia must be badly farmed, otherwise artificials would not prove so potent. The tendency all the world over is that as the soil becomes more fertile artificials produce less and less result until the effect passes off altogether. Bad farming and an experimental technique which will not hold water are poor foundations on which to found a policy. The use of replicated and randomized plots, followed by the higher mathematics in interpreting the results of these small patches of land, can do nothing to repair the fundamental unsoundness of the Tocklai procedure. It stands self-condemned. Further, the advocates of sulphate of ammonia for the tea plant seem to have forgotten that a part at least of the extra yield obtained with this manure may be due to an increase in soil acidity. Tea, as is well known, needs an acid soil: sulphate of ammonia increases acidity.

The humus school of thought takes the view that what matters in tea is quality and a reserve of soil fertility such as that created by the primeval forest: that this can only be obtained by freshly prepared humus made from vegetable and animal wastes and by the correct use of shade trees, green-manure crops, and the prevention of soil erosion. The moment the tea soils can be made really fertile, the supply of nitrogen to the plant will take care of itself and there will be no need to waste money in securing the fleeting benefits conferred by artificials. The problem therefore of the manuring of tea is not so much the effect of some dressing on the year's yield but the building up of a store of fertility. In this way the manurial problem and the stability of the enterprise as a going concern become merged into one. It is impossible to separate the profit and loss account and the balance-sheet of a composting programme because the annual dressings of humus influence both.

It will be interesting to watch the results of this struggle in a great plantation industry. At the moment a few of the strongest and most successful groups are taking up humus and spend little or nothing on artificials. Other companies, on the other hand, are equally convinced that their salvation lies in the use of cheap chemical fertilizers. Between these two extremes a middle course is being followed -- humus supplemented by artificials. Mother earth, rather than the advocates of these various views, will in due course deliver her verdict.

Can the tea plant itself throw any light on this controversy or is it condemned to play a merely passive role in such a contest? Has the tea bush anything to say about its own preference? If it has, its representations must at the very least be carefully considered. The plant or the animal will answer most queries about its needs if the question is properly posed and if its response is carefully studied.

During the early trials of the Indore Process it became apparent that the tea plant had something very interesting to communicate on the humus question. Example after example came to my notice where such small applications of compost as five tons to the acre were at once followed by a marked improvement in growth, in general vigour and in resistance to disease. Although very gratifying, in one sense these results were somewhat disconcerting. If humus acts only indirectly by increasing the fertility of the soil, time will be needed for the various physical, biological, and chemical changes to take place. If the plant responds at once, some other factor besides an improvement in fertility must be at work. What could this factor be?

In a circular letter issued on October 7th, 1937, to correspondents in the tea industry, I suggested that the most obvious explanation of any sudden improvement in tea, observed after one application of compost, is the effect of humus in stimulating the mycorrhizal relationship which is known to occur in the roots of this crop.

In the course of a recent tour (November 1937 to February 1938) to tea estates in the East, I examined the root system of a number of tea plants which had been manured with properly made compost, and found everywhere the same thing -- numerous tufts of healthy-looking roots associated with rapidly developing foliage and twigs much above the average. Both below and above ground humus was clearly leading to a marked condition of well-being. When the characteristic tufts of young roots were examined microscopically, the cortical cells were seen to be literally overrun with mycelium and to a much greater extent than is the rule in a really serious infection by a parasitic fungus. Clearly the mycorrhizal relationship was involved. These necessarily hasty and imperfect observations, made in the field, were. soon confirmed and extended by Dr. M. G Rayner and Dr. Ida Levisohn, who examined a large number of my samples including a few in which artificials only were used, or where the soils were completely exhausted and the garden had become derelict with perhaps only half the full complement of plants. In these cases the characteristic tufts of healthy roots were not observed; root development and growth were both defective; the mycorrhizal relationship was either absent or poorly developed. Where artificials were used on worn-out tea, infection by brownish hyphae of a Rhizoctonia-like fungus (often associated with mild parasitism) was noticed. Whenever the roots of tea, manured with properly made compost, were critically examined, the whole of the cortical tissues of the young roots always showed abundant endotrophic mycorrhizal infection, the mainly intracellular mycelium apparently belonging to one fungus. The fungus was always confined to the young roots and no extension of the infection to old roots was observed. In the invaded cells the mycelium exhibits a regular cycle of changes from invasion to the clumping of the hyphae around the cell nuclei, digestion and disintegration of their granular contents, and the final disappearance of the products from the cells.

Humus in the soil therefore affects the tea plant direct by means of a middleman -- the mycorrhizal relationship. Nature has provided an interesting piece of living machinery for joining up a fertile soil with the plant. Obviously we must pay the closest attention to the response -- as regards yield, quality, and disease resistance -- which follows the use of this wonderful bit of mechanism. We must also see that the humus content of the soil is such that the plant can make the fullest possible use of its own machinery.

The mycorrhizal relationship in tea and its obvious bearing on the nutrition of the plant places the manurial problems of this crop on a new plane -- that of applied biology. The well-being of the tea plant does not depend on the cheapest form of nitrogen but on humus and the consequences of the mycorrhizal relationship. We are obviously dealing with a forest plant which thrives best on living humus -- not on the dead by-product of a factory.

It is easy to test the correctness of this view. It can be done in two ways: (1) by a comparison of tea seedlings grown on sub-soil (from which the surface soil containing humus has been removed) and manured either with a complete artificial mixture or with freshly prepared humus, and (2) by observing the effect of artificials on a tea-garden where the soil is really fertile. Such trials have already been started. In the case of seedlings grown on subsoil manured with: (1) no tons of humus to the acre, or (2) the equivalent amount of NPK in the form of artificials, Mr. Kenneth Morford has obtained some very interesting results at Mount Vernon in Ceylon. Nine months after sowing, the humus plot was by far the better -- the plants were 10 high, branched, with abundant, healthy, dark green foliage. The plots with artificials were 6 inches high, unbranched, with sparse, unhealthy, pale foliage. An examination of the root systems was illuminating. The humus plants developed a strong tap root 12 inches long; the artificials plot showed little attempt to develop any tap root at all, only extensive feeding roots near the surface. The root system at once explained why the humus plot resisted drought and why the artificial manure plot was so dependent on watering. Mr. Morford's experiment should be repeated in some of the other tea areas of the East. The results will speak for themselves and will need no argument.

The effect of sulphate of ammonia on a really fertile soil is most interesting. As would be expected the results have been for the most part almost negative, because there is no limiting factor in the shape of a deficiency of nitrogen, phosphorus, or potash under such conditions. On old estates, where organic matter has not been regularly replaced, resulting in the loss of much of the original fertility, such an experiment would give a clear indication as to whether, under existing management, the soil is losing, maintaining, or gaining in fertility. Given an adequate supply of humus in the soil, the mycorrhizal relationship and the nitrification of organic matter, when allowed to work at top speed, are all that the plant needs to produce a full crop of the highest quality possible under local conditions. The tea plant therefore is already preparing its own evidence in the suit -- Humus versus Sulphate of Ammonia.

The problem of the manuring of tea is straightforward. It consists in converting the mixed vegetable wastes of a tea estate and of the surrounding land into humus by means of the urine and dung of an adequate herd of live stock -- cattle, pigs, or goats. As the tea districts are situated in regions of high rainfall it will be necessary in many cases to protect the heaps or pits from heavy rain. Ample vegetable waste must also be provided. The solution of the practical problems involved will necessarily depend on local conditions. At Gandrapara in the Dooars, an estate influenced by the south-west monsoon, Mr. J. C. Watson has set about the provision of an ample supply of humus in a very thoroughgoing manner, an account of which will be found in Appendix A. It cannot fail to interest not only the producers of tea but the whole of the plantation industries as well.

The conversion of vegetable and animal wastes into humus is only one aspect of the soil-fertility problem of a tea-garden. There are a number of others such as the use of shade trees, drainage, prevention of erosion, the best manner of utilizing tea prunings and green-manure, the utilization of water-weeds like the water hyacinth, the treatment of root disease, the raising of seed, the manufacture of humus from vegetable wastes only, and the effect of artificial manures on the quality of tea. These will now be briefly discussed.

Generally speaking, more attention is paid to shade trees in North-East India than in South India and Ceylon. There is a tendency for shade to decrease as one proceeds south. It may be that the factor which has determined the invariable use of shade in North- East India is the intense dryness and heat of the period March to June which does not occur in the south. As, however, tea is a forest plant and tea-growing must always be looked upon as applied forestry, it would seem to be a mistake to reduce shade too much. The organic matter provided by the roots and leaves of the shade trees, the protection they afford the soil from the sun, wind, and rain, and the well-known advantage of mixed cropping must all be very important factors in the maintenance of fertility. This is borne out by the superior appearance of the tea on well-shaded estates in Ceylon compared with that on land alongside where the shade trees have been removed.

A large amount of the vegetable wastes on a tea estate consists of prunings and green-manure plants. These are either forked in, buried in long shallow trenches, or made into humus. Is there any more effective method of dealing with these wastes? When the tea is pruned the plant makes a new bush. Could it not be induced to re-make a portion of its root system at the same time in well-aerated rich soil? I think it could. On estates provided with adequate shade and contour drains, the following two methods of composting tea prunings and green-manure might be tried out:

  1. This material should be forked in with a dressing of compost at the rate of 5 to 10 tons an acre. Decay will then be much more rapid and effective than is now the case. This method of the sheet composting of tea prunings has been tried out and found successful at Gandrapara.
  2. The prunings and green-manure should be composted in small pits between alternate rows of tea. The pits should be 2 feet long and 1-1/2 feet wide and 9 inches to a foot deep, parallel to the drains or contour drains and so arranged that the roots of every tea plant come in contact with one pit only. The pits are then nearly half filled with mixed tea and green-manure prunings, which are then covered with a thin layer of compost or cattle manure. More green material is added until the pit is nearly full. It is then covered with three inches of soil. The pits now become small composting chambers; humus is produced while the tea is not growing a crop; earthworms are encouraged; the roots of the neighbouring tea plants soon invade the pit; a portion of the root system of all the tea plants of the area is then recreated in highly fertile, permeable soil. When the pruned bushes need tipping on estates where the first picking is not manufactured, another set of similar pits can be made in the vacant spaces between the first pits in each line and similarly filled.

When next the bushes are pruned exactly the same procedure can be carried out in the hitherto undisturbed spaces between the rows of tea.

When the fourth set of pits has been made each tea bush will have completed the re-creation of a large portion of its root system in rich earth.

The first large-scale trial of the pit method was begun at Mount Vernon in Ceylon in January 1938. The results have been satisfactory in all respects. the yield of tea has increased: the plants have resisted drought: the cost of the work has proved to be a sound investment.

On several tea estates in Assam the low-lying areas among the tea are used for the growth of water hyacinth for the compost heaps. When this material forms a quarter to a third of the volume of the heap, watering during the dry season can be reduced very considerably. About three-quarters of the weed is harvested, the remainder being left to produce the next year's crop. As water hyacinth is known to diminish the number of mosquitoes it might pay a tea estate from the point of view of malaria control only to grow this plant for composting on all low-lying areas. When water hyacinth becomes widely cultivated on the tea estates for humus manufacture, the labour employed will undoubtedly carry the news to the great rice areas of Northeast India. Here one of the greatest advances in food production in the world can be achieved by the conversion of water hyacinth first into humus and then into rice.

In many of the tracts which produce tea small areas occur in which the bushes are attacked by root disease. It is probable that local soil pans, some distance below the surface, are holding up the drainage and that this stagnant water lowers the natural resistance of the tea plant. I suggested in the Report on my tour that vertical pillar drains, filled with stones, pebbles, or even surface soil, might prevent these troubles. Similar drains are used in Sweden with good results.

The weakest link in the tea industry is the production of seed. During the whole of my tour I saw few really well-managed seed gardens. It is essential that the trees which bear seed should be properly selected, adequately spaced, well drained, and manured with freshly prepared compost. Nature will provide an automatic method of seed control. If diseases appear on the trees or in the seeds something is wrong. Only if the trees and seed are healthy, vigorous, and free from pests, is the produce of such trees fit for raising plants, which in China are said to last a hundred years. The tea plant must have a good start in life.

In Ceylon particularly, attempts have been made to prepare humus without animal wastes. The results have not fulfilled expectation. The breaking down of such resistant material as the leaves and prunings of tea is then unsatisfactory: the organisms which synthesize humus are not properly fed: the residues of these organisms which form an important part of the final humus lack the contributions of the animal. No one has yet succeeded in establishing an efficient and permanent system of agriculture without live stock. There is no reason therefore to suppose that the tea industry will prove an exception to what, after all, is a rule in Nature.

One of the most discussed topics in tea is the effect of artificial manures on quality. The view is widely held that there has been a gradual loss in quality since chemical manures were introduced. One of the planters in the Darjeeling District, Mr. G. W. O'Brien, the proprietor of the Goomtee and Jungpana Tea Estates, who continues to produce tea of the highest quality, informed me in 1935 that he had never used artificials since the estates came under his management thirty-one years ago. The only manure used is cattle manure and vegetable wastes -- in other words, humus. The role of the mycorrhizal relationship in tea helps to provide a scientific explanation of these results. There can be little doubt that this relationship will be found to influence the quality of tea as well as the productivity and health of the bush. Humus and the mycorrhizal relationship cannot of course create quality where it never existed: the utmost these factors can achieve is to restore that degree of quality which any locality possessed when first it was brought from forest under tea.

Sugar-cane

The waste products of the sugar-cane vary considerably. In peasant agriculture where the whole of the megass is burnt for evaporating the juice in open pans, the chief waste is old cane leaves, cane stumps, and the ashes left by the fuel. On the sugar estates, a number of factory wastes must be added to the above list -- filter press cake, some unburnt megass, and the distillery effluent left after the manufacture of alcohol (known in Natal as dunder). The main waste in both cases, however, is the old dead leaves (cane trash), a very difficult material to turn into humus on account of its structure and its chemical composition.

Before the advent of artificial fertilizers, it was the custom on sugar estates to maintain animals -- -mules and oxen -- for transport and for cultivation. These animals were bedded down with cane trash, and a rough farm-yard manure -- known in the West Indies as pen manure -- was obtained with the help of their wastes. Soon after the introduction of artificial manures, the value of this product began to be assessed on the basis of chemical analysis. Comparisons were made between the cost of production of its content of NPK and that of an equivalent amount of these chemical elements in the form of artificial manure. The result was chemicals soon began to displace pen manure: the animal came to be regarded as an expensive luxury. The advent of the tractor and the motor-lorry settled the question. Why keep expensive animals like mules and oxen which have to be fed from the land when their work can be done more cheaply by machines and imported fuel? The decision to give up animals and farm-yard manure altogether naturally followed because the clearest possible evidence -- that of the profit and loss account -- was available. Such false reasoning is, alas, only too common in agriculture.

The reaction of the sugar-cane crop itself to this change in manuring was interesting. Two things happened: (1) insect and fungous diseases increased; (2) the varieties of cane showed a marked tendency to run out. These difficulties were met by a constant stream of new seedling varieties. In contrast to this behaviour of the cane on the large estates is that of the same crop grown by the cultivators of northern India where the only manure used is cattle manure and where there is practically no disease and no running out of varieties. The indigenous canes of the United Provinces have been grown for twenty centuries without any help from mycologists, entomologists, or plant breeders.

Why does a variety of cane run out and why does it fall a prey to disease? Sugar-cane is propagated vegetatively from cuttings. When the buds from which the new canes arise are grown with natural manure in India, the variety to all intents and purposes is permanent. On the sugar estates, however, when the buds are raised with chemicals the variety is short-lived. There must be some simple explanation of this difference in behaviour.

What happened in the early days of the sugar estates before the advent of chemicals and before new seedling canes were discovered? In the West Indies, for example, until the last decade of the last century the Bourbon variety was practically the only kind grown. There was little or no disease and this old variety showed no tendency to run out. The experience of the cultivators of the United Provinces of India has therefore been repeated on the estates themselves.

The simplest explanation of the breakdown of cane varieties is that artificials do not really suit the cane and that they lead to incipient malnutrition. If this is so the synthesis of carbohydrates and proteins will be slightly imperfect: each generation of the cane will start somewhat below par. The process will eventually end in a cane with a distinct loss in vegetative vigour and unable to resist the onslaughts of the parasite. In other words, the variety will have run out.

This hypothesis will be transformed into something approaching a principle if it can be proved that the cane is a mycorrhiza-former and is nourished in two ways: (1) by the carbohydrates and proteins synthesized in the green leaves, and (2) the direct digestion of fungous mycelium in the roots.

Steps were taken during 1938 and 1939 to have the roots of sugar-cane examined in order to test this point of view. Material was obtained from India, Louisiana, and Natal. In all cases the roots exhibited the mycorrhizal association. The large amount of material sent from Natal included canes grown with artificials only, with humus only, and with both. The results were illuminating. Humus is followed by the establishment of abundant mycorrhiza and the rapid digestion of the fungus by the roots of the cane. Artificials tend either to eliminate the association altogether or to prevent the digestion of the fungus by the roots of the cane. These results suggest that the change over from pen manure to artificials is at the root of the diseases of the cane and is the cause of the running out of the variety. We are dealing with the consequences of incipient malnutrition -- a condition now becoming very general all over the world in many other crops besides sugarcane.

These observations leave little doubt that the future policy in cane-growing must be the conversion of cane trash and other wastes into humus. The difficulty in composting cane trash, however, is to start the fermentation and then to maintain it. The leaves are armour-plated and do not easily absorb water. Further, the material is low in nitrogen (about 0.25 per cent.) while the ash (7.3 per cent. of the mass) contains 62 per cent. of silica. The micro-organisms which manufacture humus find it difficult to start on such refractory material. The problem is how best to help them in their work: (1) by getting the trash to absorb water, and (2) by providing them with as much easily fermentable vegetable matter as possible. Molasses where available can be used to help the fermentation. If humus of the highest quality is to be synthesized an adequate supply of urine and dung must also be provided, otherwise a product without the accessory growth substances will result. Given a reasonable supply of urine and dung and sufficient easily fermentable vegetable wastes like green-manure, there is no reason why cane trash and the other wastes of a sugar plantation cannot be made into first-class humus and why a sugar estate should not be made to manure itself. The conditions which must be fulfilled are clear from the work already done. Dymond has shown that before composting, cane trash must be allowed to weather a little: the weathered leaves must then be kept moist from the start. In this way the fungi and bacteria are greatly assisted. Filter press cake, dander, and other wastes all help in the process of conversion, as will be seen from the results of his various experiments carried out in 1938 in Natal (Table 2).

Table 2
Composting cane trash in Natal
Composted with
Moisture
Loss on ignition
N
Total P2O5
Available P2O5
Total K2O
Available K2O
1. Kraal manure
60.5
30.6
0.74
0.28
0.14
S.T.
--
2. Filter cake
74.2
44.0
0.67
0.68
0.52
S.T.
--
3. Kraal manure and filter cake
61.0
33.3
0.71
0.40
0.28
S.T.
--
4. Kraal manure, filter cake and molassas
64.8
34.6
0.70
0.40
0.20
T.
S.T.
5. Dunder
28.5
20.0
0.72
0.40
0.21
0.52
0.30
6. Kraal manure, filter cake, ammonium sulphate, and potassium sulphate
59.2
27.8
1.00
0.42
0.29
0.72
0.49
7. Farm composts with available materials
55.5
27.6
0.78
0.32
0.24
S.T.
--
8. Farm composts with available materials
52.2
29.6
0.67
0.89
0.56
S.T.
--
9. Farm composts with available materials
57.8
33.1
0.91
0.56
0.44
S.T.
--
10. Farm composts with available materials
41.0
30.0
0.84
0.44
0.36
S.T.
--
11. Farm composts with available materials
29.2
9.9
0.67
0.27
0.20
S.T.
--

These results are similar to and confirm those obtained by Tambe and Wad at Indore in 1935. In Natal it is estimated that 100 tons of stripped cane will yield about 40 tons of compost containing about 280 lb. of nitrogen and 160 lb. of phosphoric acid.

The main difficulty in composting cane trash must always be the correction of its wide carbon: nitrogen ratio. The problem is a practical one -- how best to bring the various wastes together in the cheapest way and then distribute the finished humus to the land. Obviously there can be no hard-and-fast procedure. The correct solution of the problem will vary with the locality: the work is such that it can only be done by the man on the spot.

The sugar estates of the future will in all probability gradually become self-supporting as regards manure. After a time no money will be spent on artificials. The change over from present methods of manuring will, however, take time, and at first a sufficient volume of high-quality humus will be out of the question because the animals maintained will be too few.

What is the best way of using the small amount of humus that can be made at the beginning? This is a very important matter. I suggest that it should be devoted to the land on which the plant material is grown. These canes should be raised in trenches on the Shahjahanpur principle (see Chapter 14) and every care should be taken to maintain the aeration of the soil during the whole life of the crop. The trenches should be well cultivated and manured with freshly prepared humus, at least three months before planting. These canes should be regarded as the most important on the estate, and no pains should be spared to produce the best possible material. Whether or not immature cane should continue to be planted is a question for the future. What is certain is that cane to be planted should be really well grown in a soil rich in freshly prepared humus. Each crop must start properly. As the supply of organic matter increases on the sugar estates the methods found to give the best results in growing these canes can be extended to the whole estate.

That the above is possible is clear from a study of the work that has been done in India and Natal. In March 1938 Dymond concluded a careful survey of the whole problem in the following words:



Next: 5. Practical Applications of the Indore Process (cont.)

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