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Chapter 3
Soil Aeration and IrrigationA New Subject
Soils in the tropics are successively affected by burning sun and by heavy monsoon rainfall. The seasonal rise and fall of the subsoil water is another factor; the variations of levels greatly exceed the variations in temperate climates. The importance becomes obvious of paying the utmost attention to such factors, and it follows beyond dispute that the relation of the plant, especially of the plant roots, to its environment must be fully studied.
In dealing with these facts Sir Albert Howard had to be a pioneer. The subject was new to scientists. The soil investigator, from the days of Liebig trained almost wholly in soil chemistry, was, it is true, beginning to turn to soil physics. As Sir Albert later took occasion to point out, the most important aspect of the physical condition of the soil is that connected with the air in the soil. (Agricultural Journal of India, Vol. XIII, Part III, 1918, pp. 416-17.) It was on the vital question of introducing air into the soil for the use of the plant that his interest was focused. In other words, the physical aspects of soil texture were only a bridge to the biological aspect, i.e. to the needs of the growing plant in its call on the gaseous contents of the soil as material for its life processes. The plant rootlets are in permanent need of the oxygen dissolved in the film of water coating the loose soil particles, and this is lost if there is not plenty of crumb structure giving pore space; without such a supply the rootlets cannot breathe; the plant perishes. The increasing attention which Sir Albert gave year by year to the problem of soil ventilation proved an illuminating first phase in shaping his ultimate views on the requirements of plants. In his imagination the plant's need of air took precedence even over its need of water.
'All living plant cells respire just as animals do, and, in the process, use up oxygen and produce carbon dioxide as a waste product. Air is therefore necessary for that part of the plant, the root system, which is below ground. This fact is well known, but the importance of continuous gaseous interchange between the soil and the atmosphere during the growth of the crop is not always sufficiently recognized. This is particularly the case in a country like India, where water is so often all important and a frequent limiting factor in crop production. The necessity for irrigation, the attention paid to dry farming methods and to water conservation, all tend to concentrate the attention of the investigator on questions relating to water and, at the same time, to obscure the importance of the air supply of the roots... Much of the want of success in some parts of India is due to deficient soil aeration, and this is particularly the case in North Bihar, where want of air causes much more damage than want of water.'
The years of intense work up to 1913 were the years of the experimental demonstration of the ideas proving the great need of securing soil aeration in India. In these years the Pusa system of the grading and shaping of fields, applied also at Quetta and subsequently with pronounced success at Indore, was perfected; an initial problem of aeration was solved on principles which could scarcely have been bettered. In 1914 appeared some observations on the need for aeration in the application of green-manures, while a full presentation of the conclusions to be drawn from all experiments was first published in the years 1914, 1915, and 1916, culminating in a lecture in 1916 to the Board of Agriculture at Pusa in which some startling suggestions were presented. The facts brought forward rested throughout on a double series of experiments, carried out alternately on the humid plains of Pusa and on the arid desert soils of Quetta, where, however, the work tended rather to illustrate the allied subject of irrigation. The two-fold basis had been widened by notes taken in the course of tours to other parts of India; thus the insight gathered during the nine years since the start of the experiments in 1905 ended in a comprehensive view of the whole problem.
The aims were throughout practical. The Howards realized that there was, indeed, an unexplored scientific problem awaiting investigation in the sorting out of the many intricate and still unknown interchanges in the gaseous contents of the soil. At that time no study had yet been made of these phenomena in India; even such a simple truth as that rain is superior to other waterings because of its dissolved oxygen supply was new. (Agricultural Journal of India, loc. cit., p. 424.) Much work would certainly have to be done, but there was no need to wait for it. By making use of field observations it was quite possible to advance in practice. Great improvements could be quickly effected by obvious methods within the reach of all the best cultivators. On this question, as on so many others, work was strictly adjusted both to the needs and to the capacities of the Indian peasant.The Natural Soil Conditions
Broadly speaking, there are two quite distinct types of soil in India, the alluvium of the Indo-Gangetic plain, stretching right across the peninsula, and the black soils south of this belt. Pusa was situated on the Indo-Gangetic alluvium, and it was here that the problem of soil aeration was first brought home to the Howards.
'In the alluvium of the plains of India one of the most difficult things is to manage the soil so that its aeration is not interfered with by rain or by irrigation water. The crumb structure of fine alluvial soils which is so easy to produce, is also readily lost under monsoon and irrigation conditions. In consequence, the soil and the roots of the crops cannot obtain sufficient oxygen and in many cases carbon dioxide accumulates. The crops suffer from lack of aeration in the soil and oxygen becomes a limiting factor. This is the explanation we have suggested for a whole series of phenomena relating to crops on the Indo-Gangetic alluvium. All the facts so far obtained fit into the aeration theory and we have come to regard the surface layer of the alluvium as a vast oxygen filter, separating the atmosphere from the subsoil water which, analysis shows, is particularly poor in dissolved oxygen.' (The word 'separating' is not perhaps very well chosen, the meaning is that the surface soil, when in a proper condition, conducts the atmospheric oxygen downwards to the lower soil layers.)
But this 'vast oxygen filter' could only operate as such if the surface of the soil was kept open. There are innumerable references in the reports on the Pusa work to the crust which was so apt to form on these soils, and which, indeed, was known by a special term, the papri.
'All silt-like alluvial soils are particularly liable to run together on the surface after rain and to form impervious crusts. The Bihar soil is no exception to the rule and the breaking of the crust (papri) is a recognized operation in agriculture. Indeed, the people seem to be born with special papri-breaking sense. The formation of these crusts at once interferes with the aeration of the roots and as soon as the air supply in the soil is used up, growth stops. The presence of an excess of carbon dioxide round the roots seems to hasten the first steps of asphyxiation, which can be seen by a slow yellowing of the leaves. This is followed by a gradual wilting of the crop and the plants often die without setting seed. The moment the papri is broken and gaseous interchange is renewed, there is an almost instantaneous effect. The leaves turn dark green and the arrested growth recommences.'
How necessary it was at all times not to interfere with aeration from the surface downwards was shown in the course of the experimental work itself.
'Numberless other examples of the harm caused by over-consolidation have been observed at Pusa. In the course of the plant breeding work it is often necessary in picking off insects, in labelling plants, in removing suckers, and in studying the plants to tread a good deal between the rows. It has been found necessary to limit this as far as possible and to cultivate deeply by means of the kodar (a kind of mattock) at least once or twice during the life of the crop. The effect is always instantaneous and, even if a few roots are broken off in the process, the gain resulting from increased aeration is at once seen in the renewed growth and vigour of the plants.'
If the impact of the human foot, but more especially of the heavy rains, on the surface of the soil constituted a problem to be dealt with by continual cultivation, in which the peasants were, as a rule, masters, there was another danger in the rise of the subsoil waters.
'Associated with the rainfall are changes in the position of the underground water-level. When the monsoon begins, the level of water in the wells and rivers is at its lowest. As the rains proceed, the rivers fill up and there is a general rise in the water-level, which is shown by the upward movement in the wells... This rise of the ground water must affect the soil atmosphere and must slowly drive much of the soil air past the roots of the growing crops into the free atmosphere. In cases of sudden inundation in the monsoon, caused by the bursting of embankments, the loss of air goes on for some time until the whole of the soil is completely water-logged.'
On the black soils, south of the alluvial plains, the conditions were quite different. There was a natural aeration process which was effective, though the continuation of the monsoon might bring risks.
'The Ganges and Jumna mark roughly the line of division between the alluvium and the black soils of the Peninsula. As regards the method of aeration in the two classes of soil, nothing could be more distinct. As mentioned above, the alluvial soils have a great tendency to pack together and there is little or no natural aeration during the hot season. The black soils are quite different in this respect. They expand during the monsoon into a jelly-like mass and begin to crack after drying. This goes on all through the cold season. Further contraction takes place during the hot months and deep, wide cracks are formed in all directions. Rabi [cold weather] crops obtain an abundance of air by this process and so great is the cracking that moisture is lost and roots are broken... The cracking of these soils in the hot weather, combined with the hot winds, is a perfect aerating method... The expansion of the black soils during the monsoon, however, if long continued, might easily result in damage due to the air supply being cut off.'
Finally, the Howards had the advantage of being able to compare both sets of conditions with the widely different climate at Quetta, contrasting the moist plains with the dry desert: actually the aeration problem proved the same.
'The general agricultural conditions in the Quetta valley resemble to a considerable extent those of large areas of central Asia and are markedly different from those of India. The valley is situated at an elevation of about 5,500 feet above the sea and is surrounded by high mountains... The soil... is a loess deposit, apparently formed by accumulations of wind-blown dust, sometimes mixed with alluvium. With such a geological history and in a climate of great aridity, there have been no opportunities for the accumulation of organic matter... Most of the soil of the cultivated areas does not possess a great range in the size of the particles and behaves on wetting very much like the Gangetic alluvium. Flooding destroys the porosity and the surface runs together easily. Under the dry hot winds which are frequent at Quetta, irrigated land sets on the surface into a cement-like mass, which cracks in all directions and rapidly loses its moisture.'
The Erosion Effects of the Monsoon
Such were the soil conditions. But they could not be understood except in the light of the tremendous effects of natural precipitation taking the form of the recurring monsoon.
'The dominating factor in the internal economy of the Indian Empire is the monsoon. The well-being of the people, the commerce of the country, and the revenue collected by Government, all depend on the amount and distribution of the summer rainfall. It is not surprising, therefore, to find that the attention of the agricultural investigator in India tends to be concentrated on questions relating to the supply of water to crops. At the same time, the other factors on which yield depends are apt to be obscured and crop production comes to be regarded almost entirely as a question of water supply.'
The intense cry from the heart of the people for the longed for rains easily led them astray. It was part of Sir Albert Howard's work to point out that water itself could be, indeed, had been for centuries, a menace.
'In the basin of the Ganges... the high-lying lands are usually lighter and opener in texture than the heavy soils in the low-lying areas which often grow rice. These differences are largely bound up with the loss of fine soil particles which is going on continually, not only in any one area, but also in the Gangetic system as a whole. Locally, fine soil is being washed from the high-lying lands and deposited in the low rice areas. In this way the rain-washed areas tend to become light in texture while the heavy condition of the rice fields is maintained. Looking at the plains as a whole, a vast amount of fine silt is carried down to Lower Bengal by the Ganges and deposited in the deltaic regions in the form of new land which, after many years, becomes cultivated and grows uncertain crops of rice. This enormous transfer of fine soil by the Ganges and its tributaries from the area drained by this river represents a great loss of agricultural capital and is a great drain on the natural resources of the country.'
'Soil erosion is, however, by no means confined to Central India. In the great alluvial plains of Northern India, where, at first sight, the country seems quite flat, the amount of damage done by rainwash is enormous... The loss of soil by denudation in the valleys of the Ganges and Jumna is only generally recognized when the erosion has proceeded far enough to cut up the country into deep ravines, which generally run back from the rivers or low-lying areas. While this ravine formation is the most obvious result of the scour, nevertheless it is likely that this form of damage is of far less importance than the slow removal of fine soil from all the high-lying portions of the plains. This form of erosion is not very obvious at first and can only be appreciated after constant observation of the run-off during periods off heavy monsoon rainfall. The muddy water running down to the drainage lines is exceedingly rich in fine particles and this unchecked denudation has, in the course of years, brought about very definite results in the consistency of the soil. The upper lands have become open and sandy through the loss of fine particles, while the low lands have become stiff and heavy by the continued addition of new soil. The consequence is that the high lands have lost to a great extent their power of retaining moisture and only yield crops with the help of manure. The low-lying rice-fields have received more and more silt and the thickness of stiff soil has increased without any corresponding benefit to these areas.'
'A consideration of the above examples of erosion in India leaves no doubt that the natural agricultural capital of the country, the soil, is slowly running to waste. This loss of fertility reacts on crop production and therefore on the well-being of the people. This impoverishment means debt, increased liability to diseases like malaria, and finally rural depopulation. The gradual denudation of the soil of the country is the real "economic drain" on India. A little consideration must show that the first condition of improving crop production in India is to take steps to stop this constant erosion and to keep the cultivated soil in its place. Unless denudation is stopped and the fine soil is retained, it is clear that the provision of improved varieties of crops, of irrigation facilities, of improved credit, of better cattle and implements will not yield their full results.'The Water-logging of Fields
To forestall these evils the population had from ancient times used systems of embankment.
'There are two weak points in the system of embankments in Peninsular India which are of some importance. Although in many places where the soil is deep, where the slope of the ground is comparatively small and where people are energetic, embanking is a common practice and much good results, nevertheless there is hardly any provision for the discharge of the surplus water. The whole of the rain is often held up and the fields become shallow ponds. This is a disadvantage in two ways. In the first place, to hold a large volume of water for a long time, even where the slope is small, the bunds have to be made very strong and one or two breaches in a series might easily lead to very general damage to the whole, and to the escape of a large volume of water, which would take with it much valuable soil. Where the slope is considerable, these difficulties increase and sudden heavy falls would be almost certain to break a whole series of embankments. The serious disadvantage of the existing system is the practical certainty that the flooding of the land for long periods must lead to denitrification and consequently to diminished rabi [cold weather] crops. The wheat crop in many parts of the Central Provinces certainly looks as if it is suffering from a lack of available nitrogen and the whole subject seems well worth investigating from this point of view.'
Of the two connected evils, actual soil loss and waterlogging, the more persistent damage was to be attributed to the latter, which thus outweighed even the evil of the washing down of soils.
'The degree to which water-logging takes place in India varies greatly. Every gradation is to be seen from slight damage to a crop to the production of saline efflorescence and the formation of permanent, stagnant swamps in which no cultivation at all is possible beyond a little precarious rice-growing near the edge. The occurrence of slight water-logging can only be detected by a trained observer, who has learnt how to read his practice in the plant. The production of swamps, on the other hand, is of course obvious to all, but between these two extremes a vast amount of damage to crop production is being done every year which is only very dimly understood at the present time.'
Waterlogging meant depriving the plant root of air, and that, in the opinion of the Howards, was the ultimate sin. The following short passage may be some explanation of Sir Albert Howard's criticisms in later years of official agricultural research. Certainly the folly of carrying out advanced variety trials without first mastering the elementary lesson of how to manage the soil which was to support the crop would have struck any intelligent observer.
'Just as increased aeration means better root development and better growth so diminished aeration leads to a poor yield. Waterlogging during the monsoon and the absence of surface drains are the chief causes of poor soil aeration and poor root development. Examples are to be seen everywhere and were particularly well marked a few years ago on the old manurial plots and variety trials at the Government farms all over India. I never saw one of these series that was not ruined by obvious want of drainage and by waterlogging. The aeration factor was almost greater than any difference in the yielding power of the varieties or of the manures.'
The Remedy: the Shaping of Fields
What was to be the answer to these evils, which amounted to a kind of endemic disease of the soil, going back for centuries? The first thing which the two research workers had to do, if they did not wish to sink to the unfortunate level of their fellow workers of the old manurial trial plots just referred to, was to use their eyes. There were natural indications, full of significance, which could be noted at Pusa and could lead in the right direction.
'The most startling results of natural aeration are, however, to be seen after trees have been felled or when holes (such as the brick-soaking tanks used in building operations) have been filled with new earth. When a tree has been cut down and the roots have died, the white ants become active and proceed to eat out the whole of the cylinder of wood, leaving the bark behind. The result is that there is a perfect network of connecting tubes under the surface, which greatly promotes the aeration of the soil and of the roots of crops. The effect of this becomes very marked about a year after the trees are cut down and the results on the crop are similar to those obtained by heavy dressings of nitrogenous manure. The increased aeration obviously acts in two ways. In the first place, a plentiful supply of air to the roots is supplied. In the second place, the formation of nitrates by the soil bacteria is considerably increased. There is a very good case in the Botanical Area [at Pusa] at the present moment of the effect of old roots on succeeding crops. A line of sissoo trees... was cut down in 1910. In 1911 it was observed that the edge of the plot next to the former line of trees was becoming exceedingly fertile. The effect is still more evident during the present year (1914) and the wheat crop on the east side of this plot will have to be cut back to prevent lodging later on. This result is a consequence of the work of the termites in removing the wooden cores of the roots. These insects are always attracted by old wood, which they rapidly devour. In addition to assisting in the transformation of vegetable matter into humus, these insects are most useful as aerating agents and their systematic destruction, as is sometimes advocated, would, if successful, only lead to great loss to India.' (Sir Albert considered that the termites did the same work of soil aeration in tropical climates as is carried out by the now famous earthworm in temperate zones.)
The Indian peasants were not without their own faculty of observation. They had evolved more than one clever device. It has already been stated that they seemed to be born with an inherited 'papri-breaking sense'. They were ingenious also in taking advantage of the better aeration to be found on the borders of irrigated field, what was called 'the edge effect'. Plants thus located could reach a supply of air through the earth embankment and grew much better than those in the centre of a plot where the soil was waterlogged. It had become habitual practice for the ryots, when requiring patwa (Hibiscus cannabinus L.) or sann (Crotalaria juncea L.) for seed, never to sow in field patches, but always to have a few plants on the edges of the field, which were often slightly raised; experience had shown that only in this way would these plants come to maturity. It was interesting that Europeans, growing vegetables on the black soils, had copied this idea of sowing round the edges of plots in order to escape waterlogging.
Perhaps even more important was the widespread knowledge and use of the deep-rooting plant as a natural soil aerator. Many plants could act in this way by the thrusting nature of their root systems, rahar (Cajanus indicus) being one of the best examples. It was a well-known practice to grow rahar before tobacco, a crop requiring especially good aeration, and also usual to breakup soured airless packed soil under rough grass land (perti) by means of a first crop of the sweet potato, which managed to thrive in conditions which would choke other crops and whose swelling roots, acting 'like a mild explosive', shattered the soil for the next crop. In the Quetta valley local knowledge dictated the use of busunduk (Sophora alopecuroides), a common weed, among the peach trees or melons; this was a plant provided with thick underground stems bursting open the subsoil in all directions and with shoots coming to the surface and letting in extra air; where this was found there was seldom yellowing of the peach; it could well be called 'the subsoil plough of the Quetta valley'. Alternatively shaftal(Persian clover), a valuable fodder, could be cultivated and ploughed in, the organic matter thus added assisting the excellent aeration effects of the deep taproot and numerous laterals, which broke up the soil in all directions. (It was on a similar experience of the soil shattering work of local deep-rooting crops that Elliot, who had spent many years in the East, based his well-known Clifton Park system of using the deep-rooting crop as a natural aerator and fertilizer.)
Such practices were only palliatives for soil conditions which had slowly degenerated over the centuries. Something more definite was needed. The remedy was found by adopting the very old principle of 'divide and rule'. The rainfall was to be dealt with field by field, and in that way mastered: the monsoon was to be 'put in harness'.
A new system was devised of the separate contouring and shaping of each field, so that it could absorb the maximum amount of water on the spot. This was something quite different from the ordinary practice of terracing. Each field was independently treated, sloped from the centre very gently downwards towards the edges to end in grass-covered drainage ditches. Thus every small area was trained to deal with its own rainfall and was also protected from the run-off from other areas, which is what is meant by the words 'divide and rule'. The idea seems to have been original, but a journey to north and central Italy while on leave in 1913 showed an almost identical system in use, and a few improvements were borrowed from what was seen in that country. (Report of the Imperial Economic Botanist for the Year 1912-13, pp. 17-18.)
'A drainage system, suitable for the Gangetic alluvium, which at the same time prevents soil erosion, has been worked out during the last few years at Pusa... The method consists in dividing up the country into areas of from five to ten acres and surrounding these with trenches, the borders and sides of which are turfed to prevent cutting. The field trenches communicate with larger channels which carry the run-off either to low-lying rice areas or to streams and rivers. The size of the field trenches will vary according to the amount and distribution of the rainfall. In Bihar, it has been found that channels four feet broad at the top, two at the bottom and eighteen inches deep, suffice in most cases. A grass strip, about a foot wide, should be left on the field on each edge of the trench to prevent breaching by the run-off, and it is an advantage to let the grass grow on the sloping sides as well. The roots consolidate the soil and, after the first year, there is little trouble from breaches. A good deal of attention is necessary during the first monsoon in repairing the edges and in checking cutting. It is best to dig the trenches in the hot weather and to plant the sides and edges with dub grass in the early rains. During the monsoon the trenches silt up to some extent and it is necessary to clean them out every hot weather, the soil being placed on the down side. A trimming up after the monsoon also adds to the general appearance of the fields... By this method each field deals with its own rainfall only and water-logging is prevented.'
'One precaution is very desirable in grading land in India. As is well known, the surface soil is always richer than the subsoil. Any concentration of surface soil in one place and any corresponding exposure of the lower soil layers in another leads to uneven growth, which does not disappear for some years. It is best therefore before beginning the grading to scrape off the upper three or four inches of the soil and to collect this on one edge of the field, The subsoil is then graded to the extent desired, after which the upper soil is rapidly and evenly spread over the whole with the ken. In this manner even crops result.'
'In Baluchistan all grading is done by the ken, which is nothing more than a slightly curved board, provided with a handle above and rings at the side for attachment to the yoke. The lower edge, which acts as a scraper, is strengthened with sheet iron. The size is roughly 3 ft. by 2 ft. 4 ins., and one pair of cattle is commonly employed. The local labour is exceedingly expert with this primitive grader and they rapidly and accurately prepare for irrigation the narrow terraces on the slopes of the valley. Earth is collected from the high places and deposited in the low areas by simply altering the slope of the ken. In an intermediate position the instrument carries its load of earth without disturbing the level of the ground passed over.
'In the Punjab a very similar instrument drawn by two pairs of cattle, known as the karah, is in use... The taking of levels is not necessary as the workmen can prepare by eye the desired slope with remarkable accuracy.'There was no other piece of work done by the Howards in the early years at Pusa of greater usefulness than this device of the draining and shaping of fields. It was a straightforward practical reform which could be brought to the notice of the Board of Agriculture, when addressed at Pusa in 1916, as within the capacity of the peasants, capable of being carried out with existing tools, yet leading to immense benefits of a permanent kind.
The Use of Potsherds in Green-manuring
An entirely different attack on the problem of aeration was made after the fielding system had become well established. The new advance was made in an almost fortuitous way; yet not really so, for it came about, as did so much else, as a result of Sir Albert's acute and penetrating observation. It was in 1915, the year previous to his address to the Board of Agriculture, that in the course of one of his journeys Sir Albert noticed an effect near Jais in Oudh which led to an explanation of the aerating effects of using potsherds or brick to dress the land. This was an Indian practice, not an Experiment Station suggestion. In view of the revival of stone mulching in horticulture, this ancient practice is of interest.
'Jais is an old Mohammedan city, standing high above the surrounding plain, and the mounds on which the town is built are composed of the remains of the ancient city of Udianagar. Large stretches of very fine tobacco are grown on the lower land surrounding Jais and the crop is irrigated from wells. In the present year (1916) I again had occasion to pass Jais and took the opportunity of examining the tobacco cultivation. The soil is rich in potsherds, derived no doubt from broken roof tiles and water-pots, and the water used in irrigating the tobacco was said by the cultivators to be unfit for drinking but very good for this crop, in the growth of which they stated very little manure was used. This was remarkable considering the excellent crops and the fact that this plant will not thrive in the absence of abundant nitrogenous food materials.'
A large sample of the irrigation water was sent for analysis to the relevant department at Pusa and was found to be exceedingly rich both in nitrates and in dissolved oxygen. (Potassium nitrate 34.57, sodium nitrate 16.55, dissolved oxygen 0.725, as contrasted with nil to 0.036 for both nitrates and 0.067 to 0. 153 of oxygen in Pusa water.)
It is not quite clear exactly at what point actual experiments in dressing soil with potsherds (thikra) were begun at Pusa, but they are referred to in several papers about this time. The rate of application was fifty tons of broken tiles to the acre, mixed with the upper six inches of soil. The results in conjunction with green-manuring are said to be 'exceedingly striking'. It was, in fact, in sorting out the erratic effects of green-manuring that the use of thikrawas to prove illuminating; the success or failure of green-manuring was found, like so much else connected with the soil, to depend on aeration.
Green-manuring is important in India because animal manure is so insufficient in quantity. But many failures in using green-manures, especially on the alluvium, were registered. It was not realized that the green-crop, while growing, used up the available oxygen supply in the soil and also released a large quantity of carbon dioxide; when subsequently ploughed in any remaining oxygen would be called on to assist decay. The crop thereupon sown, deprived of oxygen and choked by the presence of the carbon dioxide, instead of benefiting from the manurial operation, starved. This was less likely to happen in light porous soils where air could freely enter, such soils as those of North Germany where the original green-manuring experiments of Schultz-Lupitz had been carried out. But on the compacted alluvium of India, the lack of air was fatal for the growing of the succeeding crop.
That extra aeration, or special attention to aeration, was essential in a green-manuring operation had already been established in a special experiment on three tobacco plots green-manured with sann at Pusa in 1913. Green-manuring was carried out on successive dates in July and August and across all three plots a strip was subsoiled to a depth of twelve inches two days before the tobacco was transplanted at the end of September. The effect of the extra air supply given by the subsoiling was plain to see on all three plots; the first plot, where the green-manuring had been earliest carried out, gave the best results; the worst results were found where the green-manuring had been done last, thus showing that the decay of the green-manure was a process competitive with that of the growth of the crop.
'The simplest explanation of these results appears to be connected with the part played by air in the soil. The soil is usually regarded as a mass of small particles, arranged in various ways according to the degree of consolidation, with free spaces between these bodies known collectively as the pore space. Surrounding the solid particles are films of water of various thicknesses, while the rest of the pore space is taken up by the soil air. The proportion of the pore space filled by air and water naturally varies with the general wetness or dryness of the soil. The closeness of packing of the solid particles varies greatly, after a crop is sown, as a result of consolidation by irrigation water or rain. In the water films round the particles there is intense biological activity. Numerous bacteria are rapidly reproducing themselves, while the root hairs of the crop are competing with these soil organisms for water and inorganic food materials. All the protoplasm of these organisms is actively respiring and, in consequence, there is, in the water films round the particles, a keen struggle for oxygen and a great development of carbon dioxide. Under such circumstances it is easy to understand how it is that analyses of the general soil air often show a high proportion of carbon dioxide and a comparatively low percentage of oxygen.
'We must now consider what is likely to happen if this normal struggle for dissolved oxygen in the soil between the roots of the plant and the soil organisms is complicated by the sudden addition of a green crop like sann. In the first place, the growth of the green crop itself will naturally lead to a considerable pollution of the soil atmosphere by carbon dioxide. As soon as it is ploughed in, decay begins and an enormous quantity of oxygen is used up in the process, which is by no means complete when the sowing time of a rabi [cold weather] crop comes round. The partly decayed organic matter adds a new competitor in the struggle for oxygen. It is easy to understand how the remains of the green crop might easily use up the oxygen in the pore spaces and load the soil atmosphere with carbon dioxide to such an extent as to poison the air dissolved in the water films. Oxygen starvation and carbonic acid poisoning would affect the plant and growth would be checked.'The only cure was aeration and the Pusa experiments with potsherds were sufficient proof.
'Practical planters and cultivators who have seen the preliminary experiments are convinced that the maximum tobacco crop can be grown with green-manure alone on drained land treated with thikra. The experiments are most conclusive and there is no doubt that, given sufficient moisture in the soil for decay, the factor on which green-manuring depends in India is abundant soil aeration. Aeration also explains why green-manuring on the open sands of North Germany has been so successful. These soils are of such texture that they aerate themselves. On the plains of India we must overcome poor aeration by drainage and thikra.'
Provided, then, that soil aeration could be made 'copious' by surface drainage of the fields on the Pusa system, by subsoiling before sowing, and above all by the potsherd dressing, complete decay, in good time, of the green-manure could be ensured and its nitrification. This was the explanation of why the Jais water was so rich in nitrates. It was also found rich in potash, which Sir Albert attributes to the fact that much wood and cow-dung were burnt for fuel in rural centres. Such potash, together with phosphates, was, in the presence of adequate oxygen, collected by the soil fungi for the use of the higher plants; the cycle was thus complete.
'The Jais tobacco fields can be regarded as a natural manure factory in which nitrates, potash, and phosphates are produced in sufficient quantity for crops like tobacco, maize, and poppy, which are all grown on the lands in question. In spite of the fact that maize is followed by tobacco or poppy the same year and that a relatively small amount of manure is used, the tobacco crops are luxuriant and the cultivators are obviously prosperous and well to do. The sources of the nitrogen and minerals used by the crops are evidently the crop residues and the manure supplied for the maize crop. That this organic matter produces such excellent results is, in all probability, a consequence of the copious aeration of the soil produced by the great number of potsherds present...
'It is evident that in the soils of India, the great factor in manuring is aeration and that Jethro Tull's great generalization that "cultivation is manuring" can now be extended and summed up in the phrase: manuring is aeration. The potsherd enables us permanently to aerate the soil; and thus make the best use of organic matter including green-manures. The potsherd by itself has only a limited value, but with the help of small quantities of organic matter extraordinary results are possible, as the example of Jais is sufficient to indicate.'Cheap and simple devices always appealed to Sir Albert. In the Indian potsherd he had something after his own heart.
'In future in India the cultivator will go on burying his savings as before, not however as rupees, but in the form of a permanent manure -- thikra. In this manner, silver can be transmuted into gold and the dreams of the old alchemists will become a reality. The philosopher's stone is a potsherd.'
The theme of the vital need for allowing air to penetrate into the soil is repeated like a kind of leitmotif in almost every paper published about this time, 1910-16. From a very early date the Howards were impressed by the importance of the problem. Their field work was always directed to take it into account, and lysimeter experiments bore out the field work. Every trial told the same story, that the plant root needed air, but that air was not always easy to conduct into the soils of India by reason alike of the violent impact of the monsoon rains and the rise of the subsoil waters; unless prevented there would be the evil of waterlogging, to drown the plant roots, or the other evil of compaction of the surface, to choke off the air. On wheat, for instance, the verdict could not have been more decided: 'After growing wheat in Bihar for nine years, we are convinced of the importance of aeration for this crop and equally convinced that over-consolidation (of the soil) from any cause is very harmful.' A similar verdict was applicable to indigo and tobacco, to lucerne, gram, grass, and vegetables, while in the growing of fruit trees, both at Pusa and at Quetta, the aeration factor had given rise to effects of really startling definiteness. (See Chapter 5.) All results seemed to run together and even slight causes to lead to almost irreparable damage, so that to the general judgment that 'proper relations between air and water in the soil' are a necessary prerequisite for growing the best crops in Indian conditions could be added the stranger dictum that 'water, when it excludes air from the roots, acts as if it were a poison to crops'.
Irrigation: the Furrow System
This pre-occupation with the damage which water can bring was a view unusual in India, where water is valued as one of the most precious of commodities. The benefits conferred on India by the great canal systems built by the British administration, more especially in the Punjab, are a matter of common knowledge; vast new areas of land were opened up for settlement. Sir Albert was interested in the general theory of irrigation systems; as an agricultural botanist, he judged the benefits by the growth of crops and did not always agree that these had been as permanently useful as was supposed. There were risks involved, which were apt to be overlooked.
In local practice at Pusa an error was met with at the outset. This had to be put right, which was not difficult, but he might have argued that with so experienced a population it ought not to have occurred. However, the growing of fruit in India was always rather careless and deficient, possibly because fruit is never an essential subsistence crop. In arranging to water the peaches, loquats, almonds, etc., planted on arrival at Pusa -- these plantings were almost the first of the experiments -- he found a system in use among the local cultivators which might be called a small basin system. Shallow circular holes were excavated round the stems of the trees, connected by means of small trenches, and the water flooded in. Not only did this flooding invite collar-rot and the general waterlogging of young trees, but the water failed to reach far enough to benefit the further growing root-tips of the older trees; meanwhile manuring and drainage were interfered with in the monsoon.
'The disadvantages of flooding the surface are well known. Besides the destruction of the tilth and the formation of a surface skin (papri), which becomes hard and impervious on drying, this method leads to a great loss of water by evaporation. Moreover, in many cases percolation is slow, as the air in the soil can only escape very slowly laterally. Further, flooding the surface often leads to an infertile condition of the soil, due possibly to the partial destruction of the bacterial flora thereof.'
It was therefore better to replace the basins by shallow rings corresponding to the outer spread of the branches. The water, conducted by a trench parallel to the lines of trees, was sent first into the furthest ring and after that into the nearer ones, one after the other, each inlet to a ring being controlled by a small earthen dam. This simple alteration carried a number of advantages. No more water was used: it reached the growing rootlets of the trees: there was no waterlogging. During the monsoon the rings were filled in to be re-made the following season, but the parallel trenches were left and acted as good drainage canals. This system was being adopted in the United States. (Furrow irrigation was so new in India that when introduced with pruning by Dr. Martin-Leake at Cawnpore for oranges he was challenged by the buyers of the crop in flower to offer compensation for expected loss of harvest; in the event the weight of the crop was so great that it nearly broke the branches.)
'In connection with the manuring of trees this system of irrigation has proved most useful. One of the difficulties of applying manure to fruit trees in India is the subsequent damage done by white ants (termites), which are attracted by the organic matter of the manure and frequently turn their attention to the tree and destroy it. If the trees are manured just before the rings are made, and if care is taken to apply the manure only to the ring of soil just underneath the outside branches, the first watering not only tends to rot the manure but also to drive off the termites.'
An adaptation of this same device of furrow irrigation was very successful in preventing losses in the transplanting of tobacco.
'The great danger in growing a crop like tobacco, especially where the autumn rains fail, is the loss of plants which occurs on transplanting them in the field and also from grasshoppers. The usual method in India is to transplant in the evening, to water the young plants and to cover them with nim leaves during the heat of the day. Even when every care is taken, many plants die. In plant-breeding work this loss is of great importance owing to the danger of a dead plant being replaced by one of a wrong variety. In order to minimize this loss, I have devised the following method. After cultivation and manuring are finished, furrows about one foot wide and four inches deep are laid off at the proper distance so that there will be a furrow between alternate rows of tobacco. These furrows are then filled with water several times, and the water is allowed to percolate laterally until the soil is well moistened between the furrows. Transplanting is now carried out in the soil moistened by lateral seepage from the trenches, and the young plants are covered with nim leaves during the day which are removed at night. When this method is used, the loss of plants is not more than 1 per cent, and there is practically no danger of destruction by grasshoppers. During the last year, when the failure of the autumn rains almost destroyed the tobacco crop of the cultivators in the district, no difficulty was experienced in growing good tobacco at Pusa.'
It is interesting to see in this example how a mistake in practice had opened the door to insect attack, and how easily such attack was afterwards prevented by attending to the state of the soil.
The Saving of Irrigation Water in Wheat Growing
Armed with these successes at Pusa the Howards proceeded to Quetta for the summers from 1910 onwards. There they found an elaborate system of irrigation applied to the growing of wheat.
'The usual method of irrigation is by means of the karez. This is an underground ditch on sloping land, which collects the subterranean water near the hills and discharges it on to the surface. It is really an adit with a slight slope, driven into a fan talus with a much greater slope of 300 to 600 feet per mile. The land below the opening of the karez is watered by gravitation.'
'The feature of the irrigated wheat-growing area round Quetta is the large amount of fallow land and the concentration of the available irrigation water on a comparatively small area. Land is abundant but water is scarce... When Canopus appears in September, the preliminary watering is given... after forty days the first irrigation is applied, followed by the second at the end of December. Watering is stopped during the months of January and February and the third irrigation is given at the end of February. There is then a cessation while the crop is shooting and the fourth application takes place about the middle of April, followed by at least two more at intervals of about fifteen days till the grain has formed. Including the preliminary irrigation before sowing at least seven waterings are given for irrigated wheat.'There were, it is true, other methods of growing wheat without irrigation, on dry farming principles, but the crop was always precarious, and the best yields were undoubtedly obtained under irrigation.
One could have supposed that scientific advice would take the direction of encouraging the application of water and of endeavouring to increase the scope and intensity of irrigation practices. This did not commend itself to the Howards. Instead, the problem was viewed from a revolutionary aspect, the previous investigations on soil aeration being the red line guiding their ideas.
'The most interesting and significant features of the crop are the slow rate of development about the time the ears appear and the manner in which ripening takes place. The well-known changes in colour of the ears during ripening do not occur at Quetta. The ears dry up slowly from the tips rather than ripen and the full colour of the chaff is not developed. There appears to be a factor which limits the rapid ripening of the crop and there is some evidence for supposing that this is want of air in the soil, caused by the destruction of the tilth by frequent watering.'
These observations convinced Sir Albert that there was much that was wrong. Heavy watering disadvantageously prolonged the period of growth, delaying ripening, induced too great a proportion of straw to grain and a superficial rather than a deep-rooting system; above all, there was a criminal waste of the precious water itself, especially in view of the fact that the cultivators seemed quite ignorant of the uses of a dry mulch in preventing evaporation.
'If therefore the methods of growing wheat at Quetta are examined in the light of the best modern practice in arid regions, only one conclusion can be drawn. The local practices are wasteful and unscientific in the extreme. Water is thrown away in all directions: there is no effort to conserve the soil moisture and to make the best use of what is, to the wheat crop, a most timely and well-distributed rainfall. All the conditions were therefore exceedingly favourable for the conduct of water-saving experiments and, as soon as the land for the new Experiment Station was acquired, these were set in motion.'
The experiments were conducted from 1912 to 1915. Some fair results were obtained in the first year by the use of the harrow to induce a dry mulch on an unirrigated crop, but this had to be discontinued as the wheat shot up and the late rains of March, April, and May formed a distinct surface crust allowing evaporation, with bad effects on the ripening of the ear, as described above. Some additional moisture was clearly necessary, but it was a triumph to prove that the needed supply could be given by means, not of seven, but of a single irrigation.
'A single irrigation, applied before sowing... would enable a thorough cultivation of the land to be carried out before putting in the seed and would reinforce the water in the soil and subsoil to such an extent that there would be ample moisture for germination and for rapid root-development before the winter rains were received. The land was irrigated by surface flooding in the ordinary way and, as soon as the surface was dry enough, it was cultivated by means of the spring-tooth cultivator and immediately levelled with the beam. This operation is of the greatest importance in crop growing in Baluchistan both from the point of view of the saving of water and of the production of a good tilth. Irrigated land dries very quickly and unless it is ploughed up at exactly the right moment, large clods are formed which cannot be broken down by the beam. Where the area watered is several acres and the cattle power is limited, it is impossible to deal with all the land at the proper moment with such a slow-working implement as the country plough. The consequence is a great loss of moisture and a poor tilth.'
This difficulty was overcome by the introduction of a spring-tine cultivator followed by the beam. A pair of cattle could cover at least three acres in a day. Ploughing and sowing would follow, and the young crop was then lever-harrowed with a pair of cheap Canadian lever-harrows drawn by a pair of bullocks. By sloping the tines backwards this could be repeated several times. All this was well within the means of the local inhabitants. In the second year of these experiments (1915) the crop of the Experiment Station, thus treated, ripened about a month before the local crop and was far less affected by yellow rust; the full chaff colour, hardly ever seen in the country crop, was developed. The average yield for this and the preceding season was 17 maunds 29 seers per acre, or 4-1/4 maunds above the average yielded with six or seven irrigations (unmanured land in both cases).
'The real difference between the Experiment Station results and those obtained by the people can best be realized, however, by comparing the produce in both cases from the same amount of water. The zamindars water one acre seven times and obtain an average of 13-1/2 maunds of grain. The same amount of water spread over seven acres, if used according to the method employed at the Experiment Station, would give seven times 17-3/4 or 124-1/4 maunds of wheat. The difference in favour of the experiments is therefore 110-3/4 maunds of wheat. If the average irrigated acreage of wheat in the Quetta valley is multiplied by 100, the result would indicate, in maunds of wheat per annum, the present annual waste of water on this crop alone. On every 100 acres of irrigated wheat, the water now lost would produce 10, 000 maunds of grain and a large amount of straw of a total value not far short of half a lac of rupees.'
These figures applied only to the desert. But, as had been stated, there was much land lying fallow through sheer lack of water, so that the contention that a saving of waterings would mean distribution of the water thus saved to other land, and therefore much larger harvests, is true. The description ends with a brief statement that the Experiment Station work had been carried out by an Indian staff on written directions only, sent from Pusa, thus proving that the innovations suggested were not only within the financial means of the zamindars, but also within their intelligence and skill.
There was really no need to go further, and the sufficiently dramatic results, when put before the Board of Agriculture at Pusa in 1916 and at Poona in 1917, had already resulted in three resolutions of the Board and even a recommendation proposing a special Experimental Station to enquire into the question. The Howards were clearly justified in speaking with authority when they demanded an overhaul of the systems governing the use of irrigation water and its payment.
'The importance of this matter to India needs no argument... It is true that the difficulties involved in overhauling a vast system of perennial irrigation constitute a formidable undertaking. On the other hand, if, as appears to be the case, much more can be made of the present water supplies, it is obviously to the advantage both of the cultivator and of the State that modifications should be introduced into the existing systems. The centre of the subject is the plant and the physiological processes involved in its growth. If perennial irrigation interferes with its growth, it will have to be modified. The difficulty in making an advance in matters such as the improvement of an existing irrigation system is to begin. If the most is to be made of irrigation water, it is obvious that the cultivator must be a willing partner in the undertaking and that the water will have to be charged for according to the amount used. At present the usual method in India is to levy a water-rate according to the area watered, a proceeding often condemned by members of the Irrigation Department itself.'
The arrangements governing the distribution of irrigation waters were, in fact, revised by the Baluchistan Administration in consequence of the representations made. These were subsequently confirmed by three further years' work at Quetta itself, when excellent yields of wheat were obtained with a great saving of water. Similar results were arrived at in the Punjab, in Sind, and the United Provinces, while at Shabjananpur actually over thirty-three maunds were on one occasion reaped (1918-19). Elsewhere, the opposite effect, namely, the deterioration of the harvest by using too much water, was easily established.
The Supreme Importance of the Air Supply to Plants
The risks associated with over-irrigation directed Sir Albert's attention to the world-wide problem of alkali lands. The occurrence of these lands is much dreaded in India. The question was first discussed by him in a book published in 1924 (Crop Production in India, pp. 43-50), but as a further long discussion is available to all in An Agricultural Testament (An Agricultural Testament, pp. 147-55), it is not necessary to go into detail here. Briefly, the excess of sodium salts which kills plant growth is not to be attributed to lack of rainfall but to lack of air and is often brought about by perennial irrigation: once again, the four factors, soil, air, water, plant, are seen to be one problem. But if lack of aeration is the real cause of the degeneration of soils into the alkali condition, then not the washing out of the salts, which in any case is usually impossible in practice, but the opening up of the surface and the subsoil to the air by any and every means will be the only efficient remedy.
Thus in a curious and unexpected way drainage, irrigation, alkali lands, were found to be nothing but illustrations of the aeration problem. The results of surface drainage alone at Pusa had been staggering.
'The improvement in fertility and in the ease of cultivation which results from surface drainage are almost past belief. The Botanical Area at Pusa has been transformed by this means. The yields have increased, the plots produce even crops and the tilth of the stiffer areas, which was formerly poor, is now vastly improved... The most convincing proof, however, of the advantages of the adoption of this system on the Bihar estates is to be found in the rents paid by the tenants of drained land... Several areas which previously could not be let to tenants at all and which had to be put under cheap crops like oats, fetched high rents when surface-drained... The improvement in soil aeration which followed the construction of the surface drains thus rendered possible the substitution of money crops for cheap crops.'
If measures for the saving of irrigation water could be added to the field system evolved at Pusa it would seem that 'enormous progress' would be possible, and not merely in India, but in many other countries.
The subject of soil aeration eventually led in a direct way to the subject of disease. The idea that faulty soil aeration invites sickliness and failure in the plant runs through many papers, and is expressly discussed as part of the Presidential Address to the Indian Science Congress in 1926, by which time the argument had become definite. Aeration again plays its part in a consideration of the final topic, the laws governing decay. It is stressed again and again that the mixed heaps of organic waste must, if they are to break down naturally, be provided with ample air for oxidation. At a later stage, on his return to Europe, renewed aeration, by means of subsoiling, was ardently advocated by Sir Albert for English soils, as a remedy for the subsoil pans, which he strongly suspected to exist far more frequently than either the farmers or the scientists in Great Britain were ready to admit. Indeed, the immense role played by aeration in all Eastern cultivation made him impatient of the Western scientist's slowness to accept the view that plant growth must always be discussed in relation to environment: nothing in the plant could be considered by itself, it must necessarily be related to the surrounding conditions. Of these the first, even more important than water, was the air.
What was the explanation? What were the values derived from the air which made its presence in abundance so indispensable to all growth, so much so that the effects of any interference with the air supply could instantly be seen in the plant? Already in the important lecture delivered before the Board of Agriculture in 1916, when the results of the Quetta aeration experiments were being presented, Sir Albert put his finger on the crucial point. He was arguing on the subject of manuring, and in the light of his later views on artificial manures his words are prophetic. The passage is of great interest.
'Once the part played by aeration in crop production is realized, the current ideas underlying manuring will have to be considerably revised. While the application of chemical and other manures has undoubtedly increased production, its very success has worked a considerable amount of mischief and has done much to obscure the real factors on which growth depends. I will confine my remarks to nitrogen and phosphorus, the two substances on which vast sums are now spent or rather wasted.
'Nitrogen is applied to the earth either as a chemical (sodium nitrate, sulphate of ammonia, or some similar substance) or in the form of organic matter. The best results are obtained by means of the organic nitrogen manures, as these increase the porosity of the soil and help in soil aeration. Indigo seeth is the most effective form of organic nitrogen known to me. Now all this expensive nitrogen manuring is largely a mistake. The soil possesses the most efficient nitrogen producers known to science. These are the nitrogen-producing and the nitrogen-fixing bacteria which require for their work organic matter (such as green-manures or farmyard manure), air, and water. Why purchase, at a great price, the fleeting benefits of nitrogenous manures when by draining the land and adding substances like thikra (see above, "The Use of Potsherds in Green Manuring"), a crop of green-manure will supply everything that is necessary?
'Much the same state of affairs exists with regard to phosphates. Phosphates often increase the crop but, in many cases, the results are misleading. It is the fashion to say, in cases when the effect is beneficial, that the soil contains insufficient phosphates in an available form. Why is this? The answer is to be found in the mycological domain, in the beneficial activity of the soil fungi. These collect phosphates and potash for the higher plants, but they cannot do this adequately unless the soil is well supplied with air. Drainage is perhaps the best and cheapest form of phosphorus just as thikra is the best nitrogenous manure...
'The results of the permanent wheat plot at Pusa are simple aeration effects. In this direction we have possibilities of improvement in wheat production which will settle the food supply of the world for generations to come. We need pay no attention to the warnings of the late President of the Royal Society (the reference is to Sir William Crookes' famous address to the British Association for the Advancement of Science in 1898) or to the proposals in a recent issue of Nature for a committee to consider the manufacture of nitrates from the air for manuring wheat. Supply air by drainage and other means and the wheat-growing surface of the world becomes of itself a vast nitrate- and phosphate-producing factory... I feel sure that when these ideas bear fruit, a new chapter in the development of agriculture, not only in India but elsewhere, will be opened and the world's production of food and of raw materials will enter on a new phase.' (The new theory of Professor N. R. Dhar of Allahabad University that nitrogen can be fixed abiotically by direct action of the sun on organic matter would explain much in the fertility renewing capacity of Indian soils. This theory is still sub judice.)Bibliography
Agric. Journ. of India, Vol. III, Part III, July 1908: 'Furrow irrigation'.
Ibid., Vol. IX, Part II, April 1914: 'Notes on Drainage and Green-Manuring'.
Indian Tea Association Scientific Journal, 1014: 'Soil Denudation by Rainfall and Drainage and Conservation of Soil Moisture.'
Bulletin No. 52 of the Agric. Research Institute, Pusa, 1915: 'Soil Ventilation'.
Bulletin No. 53 of the Agric. Research Institute, Pusa, 1915: 'Soil Erosion and Surface Drainage'.
Bulletin No. 4 of the Fruit Experiment Station, Quetta, 1915: 'The Saving of Irrigation Water in Wheat Growing' (reprinted in Agric. Journ. of India, Vol. XI, Part I, Jan. 1916).
Bulletin No. 61 of the Agric. Research Institute, Pusa, 1916: 'Soil Aeration in Agriculture'.
Agric. Journ. of India, Special Indian Science Congress No., 1916: 'The Importance of Soil Ventilation on the Alluvium'.
Ibid., Vol. XI, Part III, July 1916: 'The Manurial Value of Potsherds'.
Bulletin No. 7 of the Fruit Experiment Station, Quetta, 1916: 'The Irrigation of Alluvial Soils' (reprinted in Agric. Journ. of India, Vol. XII, Part II, April 1917).
Agric. Journ. of India, Special Indian Science Congress No., 1917: 'The Agricultural Development of North-west India'.
The Indian Forester, 1918: 'Recent Investigations on Soil Aeration with Special Reference to Agriculture' (reprinted in Agric. Journ. of India, Vol. XIII, Part III, July 1918).
Agric. Journ. of India, Special Indian Science Congress No., 1919: 'Drainage and Crop Production in India'.
Bulletin No. 11 of the Fruit ExperimentStation, Quetta, 1919: 'The Agricultural Development of Baluchistan, Section II, Agriculture' (reprinted as Bulletin No. 119 of the Agric. Research Institute, Pusa, 1921).
Agric. Journ. of India, Vol. XX, Part VI, Nov. 1925: 'The Origin of Alkali Land'.
Crop Production in India, 1924: Part I, 'The Soil', pp. 11-49.
Indian Agriculture, 1927, Ch. II: 'The Factors underlying Production, pp. 13-16. (Extent of erosion in India.)
The Application of Science to Crop Production, 1929, pp. 43-6. (Irrigation by wells.)
Next: 4. Various Crops and Various Problems
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