|
 |
|
|
Chapter 5
The Chief Factors in the Indore ProcessThe Indore process enables the Indian cultivator to transform his mixed vegetable wastes into humus; in other words to become a chemical manufacturer. The reactions involved are those which take place under aerobic conditions during the natural decay of organic residues in the soil. The object of the process is to bring these changes under strict control and then to intensify them. A knowledge of the chemical processes involved and of their relative importance is therefore essential in applying the process to other conditions. These matters form the subject of the present chapter.
The Continuous Supply of Mixed Vegetable Wastes
A continuous supply of mixed vegetable wastes throughout the year, in a proper state of division, is the chief factor in the process. The ideal chemical composition of these materials should be such that, after the bedding stage, the carbon-nitrogen ratio is in the neighbourhood of 33:1. The material should also be in such a physical condition that the fungi and bacteria can obtain ready access to, and break down the tissues without delay. The bark, which is the natural protection of the celluloses and lignins against the inroads of fungi and bacteria, must first be destroyed. This is the reason why all woody materials -- such as cotton-stalks, pigeon-pea stalks and sann hemp (Crotalaria juncea L.) -- are laid on the roads and crushed by the traffic into a fine state of division before composting. Still more refractory residues like the stumps of sugar-cane and millets, shavings, sawdust, waste paper and packing materials, old gunny bags and similar substances, must either be steeped in water for forty-eight hours or mixed with moist earth in a pit for a few days before passing, in small quantities daily, into the bedding.
The vegetable wastes which have been utilized at Indore for the last six years are the following:
Residues available in large quantities: Cotton stalks, sann hemp -- either as green plants reaped before the flowering stage or as dried stems of the crop kept for seed, pigeon-pea stalks, sugar-cane trash, weeds, fallen leaves.
Residues available in moderate quantities: Mixed dried grass, gram stalks, wheat straw, uneaten and decayed silage, millet stalks damaged by rain, residues of the safflower crop, ground-nut husks, ground-nut stalks and leaves damaged by rain, sugar-cane and millet stumps.
Residues available in small quantities: Waste paper and packing materials, shavings, sawdust, worn out gunny bags, old canvas, worn out uniforms, old leather belting.
The chemical composition of the above or of similar materials is given in Table VI.
Table VI
Composition of the Raw MaterialsMaterial Organic matter Ash Proteins Fats Fibre Soluble carbo-hydrates Nitrogen Malvi cotton-stalks (with leaves and pericarps) 90.17 9.83 7.35 3.2 36.09 43.53 1.176 Cambodia cotton-stalks 96.91 3.09 4.00 1.11 45.31 46.49 0.64 Cambodia cotton leaves 87.45 12.55 14.06 8.49 8.71 56.19 2.25 Cambodia cotton pericarps 95.26 4.74 11.44 9.81 45.21 29.07 1.83 Mixed weeds 69.48 30.52 10.87 2.05 21.92 34.64 1.74 Sann hemp,12 weeks old, stems 96.30 3.70 4.00 1.06 53.61 37.64 0.64 Sann hemp, 12 weeks old, leaves 90.64 9.36 14.26 2.90 20.70 52.80 2.29 Sesbania indica, 6 weeks old 89.33 10. 67 14.90 3.45 22.33 48.67 2.38 Pigeon-pea stalks 91.08 8.92 4.37 1.90 39.64 45.17 0.70 Sugar-cane trash 94.09 5.91 2.00 1.25 42.16 48.73 0.32 Water hyacinth 75.80 24.20 9.37 - - - 2.17 Leaves:
(Ficus religiosa)81.37 18.63 3.00 1.33 26.89 58.18 0.48 Leaves:
(Ficus indica)82.08 17.92 2.18 1.12 28.37 50.39 0.35 Mixed dried grass 83.80 16.20 4.25 1.55 26.20 40.20 0.68 Millet stalks 89.90 10.10 2.24 - 25.42 51.57 0.70 Millet silage 89.20 10.80 4.53 1.55 26.87 51.10 0.79 Rice straw 80.90 19.10 2.25 1.05 35.10 40.40 0.36 Wheat straw 84.70 15.30 3.01 0.98 35.69 37.93 0.58 Pigeon-pea residues 86.80 13.20 11.01 4.40 19.23 44.67 1.99 Gram residues 85.70 14.30 4.68 2.27 26.71 45.86 0.75 Ground-nut residues 86.60 13.40 12.06 2.20 16.60 39.24 1.93 Ground-nut husks 85.80 14.20 7.57 2.80 55.35 13.73 1.21
It will be seen that the raw materials available at Indore differ greatly in chemical composition and particularly in the percentage of nitrogen. Many of these wastes, such as cotton-stalks, the stems of sann hemp and of the pigeon-pea, and cane trash are too low in nitrogen for rapid composting. Others -- such as green hemp, reaped just before flowering, ground-nut residues and leguminous and other weeds -- contain higher percentages of nitrogen, a portion of which is certain to be lost during the process if these materials are composted singly. A proper mixture of the various materials available, so that the nitrogen content of the mass throughout the year is kept uniform and sufficiently high, is the first condition of success. For this reason it is necessary to collect and stack the various residues in such a manner that a regular supply of dry, mixed, vegetable wastes (as already stated with a carbon-nitrogen ratio in the neighbourhood of 33:1 after the material has been used as bedding) is available right through the year. This could only be accomplished at Indore: (1) by cutting the cotton-stalks soon after picking is over so as to secure the maximum number of leaves; (2) by growing a large area of sann hemp, which contains when withered as much as 2.3 per cent of nitrogen; and (3) by securing as much green weeds, groundnut residues and fallen leaves as possible for the mixture. All these materials are rich in nitrogen, and help to bring the carbon-nitrogen ratio near the required standard. By stacking the various constituents in layers, not more than one foot thick, and by a judicious admixture with the residues richest in nitrogen, it is possible to provide a continuous supply of dry mixed material of the correct chemical composition. During the rains, a good deal of the raw material is in the form of fresh green weeds, rich in nitrogen and soluble carbo-hydrates. These must be spread, in thin layers, on the grass borders of the fields alongside the roads and withered, before being carried to the stack or used as one of the constituents of the bedding. Only in this way can the most be made of this valuable material. Collecting weeds in temporary heaps on the borders of fields leads to serious waste of the soluble carbo-hydrates and also of the nitrogen.Composting Single Materials
A number of experiments have been carried out at Indore during the last four years with the following single materials -- cotton-stalks, pigeonpea stalks, cane trash, weeds (green and withered), sann hemp (green and withered). When necessary these residues were either passed through a chaff cutter or crushed with a disc harrow before composting direct in heaps, eighteen inches high, or in pits filled to the same depth. In some cases Adco was employed as the source of nitrogen and base, in others cattle-dung and urine earth were used. Sufficient water was always added to maintain a high moisture content (Table VII).
Table VII
Moisture Content of Cotton-stalk HeapsNo. of heap Nitrogen supply and base Percentage of moisture on 3.3.30 on 15-3-30 on 3-4-30 1 Cattle-dung and urine earth 62 56 62 2 " 69 69 47 3 " 75 69 62 4 " 62 62 56 5 " 75 72 38 6 69 69 66
Although the cotton residues, fermented direct with urine earth and cattle-dung, contained 16.5 per cent of green leaves (high in nitrogen) and every care was taken to maintain the correct relation between air and water, the results were not completely satisfactory. Fermentation was rapid at the beginning, due to the presence of the leaves, but slowed down afterwards. It took I50 days to obtain a usable product, as compared with the ninety days required for mixed wastes.
In the case of cotton-stalks, broken down by the use of Adco, the results were still more unsatisfactory. Several interesting facts however came to light. The fermentation tended to be uneven; the temperature of the heaps was always irregular; the mass did not retain moisture well; a very large quantity of water was needed. The final product, although high in nitrogen, tended to be somewhat coarse and to contain a good deal of partially decomposed material Plate XI). The maximum temperatures in the Adco heaps during the first 100 days fell from 53.5 degrees C. to 29.5 degrees C. (In the standard Indore process, the range of temperature during ninety days was 65 degrees C. to 33 degrees C.) The final product was fairly satisfactory as regards fineness (80.5 per cent passed through a sieve of six meshes to the linear inch) and high in total and available nitrogen (total 2.50, available 0.42 per cent). The corresponding figures for the product made from cotton-stalks with cattle-dung and urine earth were -- fineness 84.2 per cent and total nitrogen 1.61, of which 0.13 per cent was available. In spite of the higher nitrogen content obtained in the Adco product, no increase in growth was obtained when equal quantities of both kinds of cotton-stalk compost were used in pot cultures of millet (Fig. 7). This result probably follows from the fact that the use of Adco often produces compost with a carbon-nitrogen ratio narrower than 10:1, the ideal which should be aimed at in the manufacture of humus. The extra nitrogen in such cases is always liable to be lost before the crop can make use of it.
Fig. 7. The effect of Indore and Adco composts on millet
The results obtained in the direct composting of other single materials, like pigeon-pea stalks and cane trash, were still more unsatisfactory. When used alone, either with cow-dung and urine earth or with Adco, little change took place in a month in spite of copious watering and occasional stirring. When, however, these materials were passed through the cattle-shed and used as bedding, the results were distinctly better but not really satisfactory. At the end of six months, the heaps were only about half decomposed.
Difficulties also arise when weeds (fresh or withered) or sann hemp (fresh or withered) are composted by themselves or when a mixture of the two is employed. In the first place, the nitrogen content of this material is too high and serious losses of this element take place. In the second place, these residues, particularly when fresh, tend to pack closely in the heaps and to prevent aufficient aeration (Table VIII). For this reason, withered weeds or withered sann must never form more than about 30 per cent of the volume of the bedding, the rest being made up of mixed residues like cotton and pigeon-pea stalks with a much lower nitrogen content.
Table VIII
Losses of Nitrogen Resulting from the Close Texture of the MassNo. of pit Withered materials used Total nitrogen (lb.) at the beginning Total nitrogen (lb.) in the finished product Loss or gain of nitrogen (lb.) Percentage loss or gain 34 Weeds 44.2 25.7 -18.5 -41.8 38 Half sann, half weeds 42.8 28.4 -14.5 -33.8 40 do. 49.7 29.2 -20.5 -41.3 41 Mixed residues 28.3 29.5 +1.3 +4.4
When one food material at a time is provided for the fungi and bacteria, loss of nitrogen or aeration difficulties or both always occur. When a mixed diet is employed, everything goes smoothly, provided of course all other important details receive attention.Nitrogen Requirements
The total amount of combined nitrogen which must be added to the mixed residues for the use of the micro-organisms is less than was at first expected. The vegetable wastes from the 300 acres of land at the disposal of the Institute can be converted into humus by means of half the urine earth and one quarter of the cattle-dung of the forty oxen maintained for the work of the station. A satisfactory product, with a suitable carbon-nitrogen ratio, can be obtained with this reduced supply of dung (Table IX). At first all the urine earth was employed in composting, but it was soon found that better aeration resulted with only half the quantity. Although in many cases the compost made with full dung contains about 0.15 per cent more nitrogen than that made with reduced dung, the results obtained in the field were always the same (Fig. 8). The surplus urine earth is used for manuring the land, the extra cattle-dung can either be used up in composting or can be sold for the manufacture of cow-dung cakes (kundas). This means: (1) that the present high output of compost could be doubled if sufficient vegetable wastes could be obtained; and (2) that even after this increased output is reached, half the dung would still be in excess.
Fig. 8. The effect of composts made with reduced (1/4) and full dung
Table IX
Results with Reduced (One-fourth) and Full DungNo. of pit Amount of dung used Total nitrogen (lb.) at beginning Total nitrogen (lb.) at end Percentage gain of nitrogen Percentage of nitrogen at the beginning Percentage of nitrogen at end Carbon-nitrogen ratio Fineness 14 Reduced 29.12 32.36 11.1 0.67 0.84 11.6 : 1 88.5 15 Full 32.70 34.87 6.6 0.70 0.72 12.6 : 1 82.5
The fact that the cultivator really requires only a fraction of his cow-dung for converting all his vegetable wastes into humus, disposes once and for all of the view that the salvation of Indian agriculture lies in substituting some other fuel for cow-dung cakes. This material is essential for the slow cooking needed for a vegetarian diet As no other suitable fuel. exists in many of the villages of India, cow-dung must be utilized. Fortunately, when all the available vegetable wastes have been converted into humus, a large supply of cow-dung for fuel will still be available, and there is no reason why it should not be burnt. The ashes, however, should be carefully collected and employed as a base in the compost process.
In all the comparative trials which have been made at Indore, with Adco on the one hand and with urine earth and cow-dung on the other hand, far more satisfactory results have been obtained with the indigenous materials. The weak point of Adco is that it does nothing to overcome one of the great difficulties in composting, namely the absorption of moisture in the early stages. In the hot weather in India, the Adco pits lose moisture so rapidly that the fermentation stops, the temperature becomes uneven and then falls. When, however, urine earth and cow-dung are used, the residues become covered with a thin colloidal film, which not only retains moisture but contains the combined nitrogen and minerals required by the fungi. This film enables the moisture to penetrate the mass and helps the fungi to establish themselves. Another disadvantage of Adco is that when this material is used according to the directions, the carbon-nitrogen ratio of the final product is narrower than the ideal 10:1. Nitrogen is almost certain to be lost before the crop can make use of it, particularly when Adco compost is added to the land some weeks before sowing takes place (Fig. 9).
Fig. 9. Loss of nitrogen in Adco compost
The Amount of Water Needed
It is an easy matter to waste large quantities of water in the process. As a result of repeated trials, the maximum economy of water is obtained when I68 gallons (for every 400 tagaries of used bedding) are added at the time of charging and during the next twenty-four hours. After this, the watering should proceed as laid down in Chapter IV. Any departure, in either direction, leads to a waste of water (Table X). The standard water requirements as now adopted, per cart-load of finished compost, varies from 200 to 300 gallons according to the season. The Malwa Plateau, on which Indore is situated, is a windswept area in which the humidity is low for at least eight months in the year. It is unlikely, therefore, that these quantities will be greatly exceeded, except in very dry areas like the Punjab and Sind.
Table X
The Water Requirements (in Gallons) of the ProcessNo. of pit Season Initial watering Total water for 400 tagaries of used bedding Total water per cart of finished compost 5 Cold weather 168 1208 201 Standard watering now adopted at Indore 6 168 1200 200 12 Hot weather 168 1890 315 13 168 1804 310 9 Hot weather 84 2984 479 Initial watering reduced 10 2455 72 409 11 144 2370 395 7 Hot weather 234 2044 304 Initial watering increased 8 232 2500 416
At the beginning of the process, care should be taken to add just sufficient moisture to keep the average water content below 50 per cent of complete saturation, so as to help the fungi to establish themselves rapidly and strongly. This matter is important, as the vegetable wastes take up water very slowly at the beginning. If too much is added at this stage, free water tends to accumulate in the air spaces and to hinder aeration. This checks the growth of the fungi, which thrive best if the total moisture is below 50 per cent. The moment the crumbling of the material sets in, water is absorbed more rapidly. After the first turn and till the compost is ready to cart to the fields, the total moisture content should vary between 50 and 60 per cent. After the final turn, when no more water is added, the percentage again drops to what it was at the beginning, namely under 50 per cent. During the rains, the water content of the heaps naturally tends to run a little higher than in the dry season (Table XI).
Table XI
Percentage of Moisture in Pits (Dry Weather) and Heaps (Monsoon)Pits (dry weather) Heaps (monsoon) Initial stage 43-75 68-7 46.9 65.6 50.0 62.5 After the first turn 59.4 59.4 59.4 56.2 52.3 68.7 After the second turn 50.0 62.4 50.0 62.5 54-0 62.5 56.2 62-5 52.3 - After the final turn 55.0 60.5 52.0 62.5 62.5 62.2 62.5 - Ripe manure 52.0 50.0 47.6 43.8 46.8 49.7 43.0 47.6 44.6 50.2
The depressing effect on the fermentation of very heavy monsoon downpours was well brought out during a wet period of seven days (10-16 September 1930), when 12.86 inches occurred, 11.65 inches of which were received in one continuous fall, lasting seventy-two hours. At the end of this spell, there was a temporary fall in the temperature of the heaps. Three or four days after the downpour stopped, fermentation again became vigorous as is seen by the rapid rise in the temperature (Table XII).
Table XII
The Effect of Heavy Rainfall (12.86 Inches) on the Temperature of Fermenting HeapsAge of Heap Temperature in degrees C Before the rain After the rain Three days after the rain stopped First week 61 44 53 " 59 37 50 After the first turn 55 38 52 " 54 39 53 After the second turn 51 30 48 " 48 32 48 After the third turn 41 29 38 " 40 30 38 The Supply of Air
The control of the aeration factor is perhaps the most difficult part of the process, and requires careful attention. The first condition of success in obtaining a sufficient supply of oxygen and nitrogen for the micro-organisms, is the use of mixed bedding which maintains an open texture through out the process. As already explained, single materials always tend to pack too closely and to cut off the air supply. The second condition of success is attention to detail at the time of charging. The bedding must be carefully spread, the urine earth, the cow-dung slurry and the wood ashes must be evenly scattered. Water must be properly distributed over the whole mass, and there must be no trampling. At the time of the first and second turns, the spading or forking must be carried out so that the material falls lightly, when thorough mixing takes place with the maximum amount of aeration. The third condition of success concerns the depth of the pit or heap, which must never exceed twenty-four inches. This is the maximum distance to which air can penetrate the fermenting mass in sufficient volume. If this depth is exceeded, two things happen: (1) the decay of the layers below twenty-four inches is retarded; (2) is always a loss of nitrogen through denitrification (Table XIII).
Table XIII
Compost Making in Deep and Shallow PitsPits 4 ft. deep Pits 2 ft. deep Amount of material (lb.) in charge 4500 4514 Total nitrogen (lb.) at the beginning 31.25 29.12 Total nitrogen (lb.) at the end 29.49 32.36 Loss or gain of nitrogen (lb.) -1.76 +3.24 Percentage loss or gain of nitrogen -6.1 +11.1
The air supply can also be permanently interfered with if too much earth and cow-dung are used at the time of the first charge. These materials make the whole mass too solid and pack it too closely. Anaerobic conditions are then established. This is indicated by the smell and by the appearance of flies, which then find suitable breeding conditions. The remedy is at once to turn the material, with the addition of cow-dung slurry and wood ashes. Temporary interruptions in aeration also follow overwatering or the soaking due to heavy rain. These troubles, however, pass in two or three days as the heap dries and the surplus moisture is gradually taken up by the mass (Table XII).The Maintenance of the General Reaction
In order to maintain the general reaction of the mass within the optimum range, a suitable base is necessary for neutralizing excessive acidity, and for the temporary absorption of any ammonia that may be given off during the process. The urine earth and wood ashes provide this in the most economical manner. Black cotton soil (Table XIV) contains an ample reserve of weak bases. The buffering effect of these maintains the general reaction constant throughout (Table XV). Further, black soil contains a high percentage of clay, the colloids of which are most useful in two ways. In the first place, these substances are capable of temporarily absorbing, till required for oxidation, any ammonia given off in the process. In the second place, the colloids, when mixed with the urine and cow-dung, cover the vegetable wastes with a thin, nutrient, moisture-retaining film which is of the utmost value, not only in the gradual absorption of water but also in providing the fungi with a favourable nidus for the steady breaking down of the vegetable wastes. The result is the rapid establishment of a vigorous mycelial growth, and the early crumbling of the whole mass. When a colloidal film is not employed, as in the Adco process, it is most difficult to get the material to absorb and retain sufficient moisture. Consequently, an even and vigorous mycelial growth is never quickly obtained. The colloids in soil are essential, both for coaxing water into the material and also for enabling the fungi to establish themselves rapidly and vigorously. The fungi are the storm troops of the composting process, and must be furnished with all the armament they need.
Table XIV
Mechanical and Chemical Analyses of Black SoilMechanical Chemical Fraction I II III Constituent I II III Clay 42.5 45.6 38.3 Insolubles 56.1 73.8 68.7 Fine Silt 19.6 21.8 17.7 FE203 9.8 9.1 11.2 Silt 12.5 10.8 11.3 MNO2 -- 0.1 0.3 Fine Sand 7.4 4.2 6.7 CaO 6.6 0.9 1.0 Coarse Sand 10.2 6.0 3.0 MgO 2.5 1.5 1.8 Moisture 3.3 6.4 3.0 K2O 0.4 0.2 0.4 Loss on Ignition 3.0 5.7 2.7 Na2O 0.2 - - Calcium Carbonate 1.6 6.1 1.4 0.08 0.17 0.06 CO2 0.8 0.1 0.4 0.03 0.05 0.05 Organic combined water 9.4 7.4 5.83
Table XV
Reaction and Temperature in the Indore ProcessStage pH value Temperature in deg. C One day after charge 7.2 63 After first turn (19 days old) 7.4 49 After second turn (34 days old) 7.5 45 After third turn (60 days old) 7.6 41 Ripe manure (90 days old) 7.7 35
In a recent paper, received just as this chapter was completed, Jensen has shown that cellulose decomposing bacteria multiply most strongly at pH 7.0-8.0.The Fermentation Processes
In addition to providing suitable conditions for the rapid development of the micro-organisms, it is necessary to inoculate the mass at the proper moment, so that there is no delay in the conversion. This is arranged for at the time of charging, when the pits are uniformly infected with actively growing fungus mycelium, taken from a compost pit ten to fifteen days old. At the same time, the bacteria present in cow-dung are introduced in large numbers. A further inoculation is carried out at the time of the first turn, when compost from a pit thirty days old is introduced into the mass. This provides a supply of the organisms required for the second half of the process.
The activity of the various micro-organisms can most easily be followed from the temperature records. A very high temperature, about 65 degrees C., is established at the outset, which continues for a long time with only a moderate downward gradient (Table XVI). This range fits in very well with the optimum temperature conditions required for the micro-organisms which break down cellulose. The aerobic thermophylic bacteria thrive best between 43 degrees and 63 degrees C.; the fungi between 40 degrees and 55 degrees C.
Table XVI
Temperature Range in a Normal PitMoisture 45 to 55 per cent Age Temperature in deg. C Period in days for each fall of 5 deg. C 12 hours 65 Temperature Range Days Days 65°-60° 4 3 63 60°-55° 7 4 60 55°-50° 1 6 58 50°-45° 25 11 55 45°-40° 2 12 53 40°-35° 44 13 49 35°-30° 14 14 49 First Turn 18 49 20 51 22 48 24 47 29 46 Second Turn 37 49 38 45 40 40 43 39 57 39 Third Turn 61 41 66 39 68-76 38 82 36 90 33
The temperatures throughout the fermenting mass are extraordinarily uniform in the pits; in the heaps the range is somewhat greater (Table XII). An analysis of the figures shows that, before each turn, a definite slowing down in the fermentation takes place. As soon as the mass is remade, when more thorough admixture with copious aeration occurs, there is a renewal of activity during which the undecomposed portion of the vegetable matter from the outside of the pit or heap is attacked. At least three types of fermentation appear to be involved, which succeed one another with great rapidity. Two of these -- those which occur between 50 degrees to 45 degrees C. and 40 degrees to 35 degrees C. -- are long continued. It is during these latter stages of the process that the transformation of the vegetable wastes into humus occurs, accompanied by the rapid crumbling and shrinkage of the mass. A detailed analysis of the phases of micro-biological activity and the determination of the organisms concerned has not yet been carried out. The results, when obtained, cannot fail to throw considerable light on the real origin of humus and should also help to clear up a large field of rather obscure organic chemistry. This subject can naturally be more effectively studied in the mass under factory conditions than on a small scale in pot cultures or in the laboratory.
Table XVII
Uniformity of Temperature in the Fermenting MassAge in days Method of taking readings Temperature in deg. C. Meteorological details Top Middle Bottom Humidity Max. Temp. deg. F. Min. Temp. deg. F. Rain in inches Pits -- cold weather 2 Diagonally 62 63 61 44 77 43 - 27 " 47 48 46 77.5 81 53 - 27 Vertically 46 48 48 56 39 39 38 55 70 39.5 - 90 Six inch layer removed 31 31 31 55 70 39.5 - Pits -- hot weather 2 At random 67 67 1 66 30 106 71 - 21 " 53 53.5 53 62 100 66 0.23 Heaps -- monsoon 3 At random 61 56 62 82 89 75 - 21 " 52 55 50 73.5 88 71 - 59 " 40 40 40 92.5 86 71 - 60 " 40 40 40 70-75 90.5 64 -
Wind is always a source of trouble and does most harm during the early stages of fermentation -- between charging and the first turn -- by lowering the temperature. The effect is most marked in the heaps (Table XVIII) which helps to explain why the process is not quite so efficient in the rains as it is in pits during the rest of the year.
Table XVIII
Effect of Wind on a HeapAge (days) Temperature in deg. C. Windward Leeward Three 53 64 First turn 44 56 " 47 55 Second turn 38 40 " 38 39 Third turn 39 41 " 38 40
The wind factor can be minimized during the rains by arranging the heaps so that they shelter each other. The pits must always be orientated so that the length is at right angles to the direction of the prevailing wind. This gives each pit a windward and a leeward side. The first turn must always be made towards the windward side, so that the earth wall of the pit protects the mass. Temporary spells of cold weather of short duration, such as occur in India, have no injurious effect (Table XIX). The fermentation is so vigorous that these sudden changes of temperature are not able to check the process. Hence in the tropics, compost houses are unnecessary.
Table XIX
Effect of Cold Weather on the Fermentation in A PitAge (days) Temperature in deg. C. Pit Air (Minimum) 1 65 8 1 62 11.1 1 62 6.1 1 62 9.4 4 60 11.1 4 59 8.3 4 60 4.1
The disintegrating power of the process is so intense that unbroken stems of grass and weeds, several feet in length, are reduced in ninety days to partially decayed fragments only a few inches in length. The long continued moist heat of the fermentation also leads to other useful results besides helping to soften and break down the mass. The high temperatures make the process sanitary, and prevent all objectionable smell. Flies and other insects cannot breed in the hot mass. The seeds of weeds are killed in the process, as is shown by the fact that no weeds grow on the heaps of ripe compost. To confirm this point, Is. of grass seeds were mixed with the bedding of two pits. Germination tests of the ripe manure gave negative results in each case.Gains and Losses of Nitrogen
A simple means of testing the efficiency of the process is to determine the amount of nitrogen lost. When vegetable wastes, with a carbon-nitrogen ratio in the neighbourhood of 33:1, are composted under strict aerobic conditions in the presence of suitable bases, there should be no loss of nitrogen whatsoever. If any loss of this element occurs, the process itself must be at fault. A careful nitrogen balance sheet has therefore been kept for a number of pits and heaps, which shows that under normal conditions no loss of nitrogen takes place (Table XX). On the contrary, nitrogen is gained, apparently by fixation from the atmosphere.
Table XX
Nitrogen Balance Sheets in Normal Pits and HeapsNo. Description Total nitrogen (lb.) at the beginning Total N nitrogen (lb.) in the finished product Total gain in nitrogen (lb.) Percentage gain of nitrogen (lb.) Pit 14 Standard (1/4 dung) 29.12 32.36 3.24 11.1 15 Full dung 32.70 34.87 2.17 6.6 16 Dry dung 30.41 32.33 1.92 6.3 18 Full dung (residues low in nitrogen) 29.10 36.77 7.67 26.3 19 Dry dung 29.55 30.70 1.15 3.9 20 Standard (1/4 dung) 24.73 25.80 1.07 4.3 21 32.35 33.40 0.15 0.45 Heap 42 Monsoon 22.28 29.52 1.24 4.4
In one case, No. 18, in which residues poor in nitrogen were composted with the full supply of dung, a very large amount of fixation took place. It will be interesting to investigate cases such as these in greater detail, and to determine the exact conditions under which such a large volume of free nitrogen can be fixed.
While losses of nitrogen do not take place in normal pits or heaps, waterlogging of the pits during the early rains, even for a short period, is at once followed by denitrification (Table XXI).
Table XXI
Nitrogen Balance Sheet of Temporarily Waterlogged PitsNo. Description Total nitrogen (lb.) at the beginning Total nitrogen (lb.) in the finished product Total gain in nitrogen (lb.) Percentage gain of nitrogen (lb.) Pit 24 Full dung 31.80 29.66 2.14 6.7 25 Full dung 29.55 27.10 2.15 8.1
Nitrogen is always lost in the first stage of the process -- between charging and the first turn -- whenever the nitrogen content of the mass is too high at the beginning (Table XXII).
Table XXII
Changes in Nitrogen Content during the First Stages of the ProcessNo. Description Percentage nitrogen at the beginning Percentage nitrogen after the first turn Residues poor in nitrogen Pit 14 Standard -- dry season 0.68 0.84 Pit 25 Standard -- dry season 0.63 0.60 Heap 41 Standard -- monsoon 0.64 0.64 Residues rich in nitrogen Pit 5 Full dung -- dry season 1.04 0.70 Pit 6 Full dung -- dry season 0.86 0.73 Pit 40 Full dung -- monsoon 1.30 1.03
Another loss of nitrogen which has to be guarded against takes place when the final product is kept too long in heaps. An appreciable loss of nitrogen takes place even when the compost is kept for an extra month in the heap (Table XXIII). After ninety days the process is complete, when the humus should be used as a top dressing for growing crops or else banked by applying it to the land, when it becomes diluted with such large volumes of dry earth that all further changes are checked.
Table XXIII
Nitrogen Losses during Storage in HeapsNo. of Pit Percentage of total nitrogen on dry basis after three months Percentage of total nitrogen on dry basis after four months 7 0.90 0.88 8 1.00 0.93 14 0.84 0.81 15 0.72 0.68 The Character of the Final Product
The ripe compost consists of a brownish-black, finely divided powder, of which about 80 per cent will pass through a sieve of six meshes to the linear inch. The state of division of an organic manure is an important factor, second only to its chemical composition. This property enables the Indore compost to be rapidly and easily incorporated, and to exert its maximum effect on the internal surface of the soil. The carbon-nitrogen ratio is not far from the ideal figure of 1O:1. The nitrogen is therefore in a stable form, which does not permit of liberation beyond the absorption capacity of the crop. The percentage of total nitrogen is also satisfactory, varying from 0.8 to 1.0 per cent (Table XXIV).
Table XXIV
Composition of the Final ProductNo. of pit or heap Materials used Organic Matter Total Ash Silicates and Sand Nitrogen P2O5 K2O C/N Soluble Humus Fineness Heap Cotton-stalks with reduced (1/4) dung 33.92 66.09 34.97 1.61 0.48 3.38 16.5:1 11.56 68.15 Pit 7 Dry mixed residues 20.14 79.87 46.91 0.0 0.41 1.95 11.2:1 5.56 72.3 Pit 14 Dry mixed residues 19.66 80.34 46.32 0.84 0.68 2.35 11.6:1 6.27 88.5 Pit 8 Dry mixed with full dung 20.19 79.82 46.27 1.0041.004 0.51 3.05 10.8:1 4.83 81.3 Pit 15 Dry mixed with full dung 18.39 81.62 51.33 0.725 -- 2.43 12.6:1 3.86 82.5 Pit 5 Dry mixed with full dung 19.76 80.24 50.11 0.841 0.403 2.23 11.7:1 5.29 84.0 Results obtained in the monsoon Heap 6 Mixed withered weeds 21.25 78.75 47.55 0.862 0.43 2.33 12.3:1 4.01 76.3 Heap 10 Mixed withered weeds 22.05 77.95 47.77 0.808 0.49 4.99 13.6:1 4.07 78.4 Heap 22 Mixed withered weeds 22.09 77.91 48.45 0.914 0.51 3.59 12:1 4.31 75.7 Heap 34 Mixed withered weeds 19.38 80.63 48.7 0.625 0.59 5.31 15.5:1 4.27 79.4 Heap 40 Half withered weeds, half sann 21.05 79.95 47.61 0.825 0.55 2.85 12.75:1 5.96 78.6 Heap 42 Dry mixed residues 21.69 78.32 46.41 0.806 0.62 3.65 13.5:1 5.36 84.0
The nitrifying power of the compost, particularly that made from mixed residues, is very satisfactory. Laboratory tests, carried out under conditions resembling those of the field during the early monsoon rains, gave the results noted in Table XXV. These figures bring out clearly the superiority of the product made from mixed residues.
Table XXV
The Nitrifying Power of Indore Compost under Conditions Resembling Those of the Monsoon1.22 gm. dry, ash-free organic matter and 41 mg. nitrogen added per 100 gm. of air-dry soil. Moisture during the experiments between 23 and 30 per cent. Sample After 7 days After 14 days After 21 days After 28 days Nitric nitrogen mg. % humus nitrogen nitrified Moisture per cent Nitric nitrogen mg. % humus nitrogen nitrified Moisture per cent Nitric nitrogen mg. % humus nitrogen nitrified Moisture per cent Nitric nitrogen mg. % humus nitrogen nitrified Moisture per cent Black Cotton Soil alone (control) 1.1 2.7 24.724.7 1.1 2.7 23.4 1.3 3.2 25.2 1.35 3.3 24.7 Black Cotton Soil + compost from mixed residues 1.8 4.4 23.5 1.9 4.6 24.1 2.05 5.0 24.5 2.5 6.1 26.7 Black Cotton Soil + compost from cotton-stalks 1.85 4.5 23.4 1.95 4.8 23.7 2.25 5.5 26.3 2.5 5.0 26.1
Besides its value as a source of readily available nitrogen, the Indore compost acts as an indirect manure. The permeability of the black cotton soil is markedly improved, particularly by the product from mixed residues (Table XXVI).
Table XXVI
Influence of Indore Compost on the Permeability of Black Cotton SoilPeriod of exposure Duration of percolation No. of cc. of filtrate collected Permeability ratio Black cotton soil only Black cotton soil + compost from mixed residues Black cotton soil + compost from cotton-stalks 3 weeks 2 hours 132 225 220 1:1.7:1.5 4 weeks 1.5 hours 97 164 130 1:1.7: 1.3 6 hours 195 340 280 1:1.7:1.4 The method adopted in carrying out these permeability tests is to maintain the moisture in the samples between 23 and 30 per cent as in the case of the nitrification tests. A weighed portion (150 gm.) of the moist samples is churned for fifteen minutes with 500 cc. of distilled water in a Bouyonco's soil cup by means of the electric mixer. The suspension is then quickly poured on a fluted agar filter, and the volume of the filtrates obtained during equal periods measured.
The loss of permeability which takes place in these soils after the early rains, is perhaps the greatest obstacle to high yields of cotton. A manure, therefore, which will help to remove this factor, is exactly what the cultivator needs. This property will prove of the greatest value in keeping alkali in check, when the process is applied to the close alluvial soils of the Punjab and Sind.
It will be clear from the results set out in this chapter that a solution of the problem of utilizing the waste products of agriculture itself has been solved, by methods which are well within the means of any industrious cultivator. All the recent work on the problems of manuring points clearly to the supreme importance of organic matter of the right type. This must possess a carbon-nitrogen ratio in the neighbourhood of 10:1, and must be synthesized from crop residues by means of fungi and bacteria, working under aerobic conditions. Clearly the thing to do is to manufacture such a product in a compost factory under strict control, and then to add the organic matter to the soil. This has been accomplished at Indore.
(After this chapter was written, a paper by Waksman and Gerretsen appeared in the issue of Ecology of January 1931, which confirms the results set out above in a very remarkable way, The New Jersey experiments deal with the influence of temperature and moisture on the decomposition of plant residues as a whole. The higher the temperature, the more rapid is the decomposition of the material including the lignins. At the highest temperature, 37 degrees C., the carbon-nitrogen ratio was reduced from about 1OO to 11.3:1, to almost the ratio of the organic matter in normal soil. When decomposition was most favourable and most rapid, the final carbon-nitrogen ratio was practically the same as that in soil humus. This is exactly what happens in the Indore process. The American results, which were obtained under laboratory conditions, fully confirm our factory experience of the last four years in India and can be applied, practically as they stand, to the Indore process.)Bibliography
Brayne, F. L. -- The Remaking of Village India, Oxford University Press, 1929.
Dubos, R. J. -- 'Influence of Environmental Conditions on the Activities of Cellulose Decomposing Organisms in the Soil,' Ecology, 9, 1928, p. 12.
Howard, A. and Howard, G. L. C. -- The Application of Science to Crop Production, an Experiment carried out at the Institute of Plant Industry, Indore, Oxford University Press, 1929.
Hutchinson, H. B. -- 'The Influence of Plant Residues on Nitrogen Fixation and on losses of Nitrates in the Soil,' Journ. of Agric. Science, 9, 1918, p. 92.
Jensen, H. L. -- 'The Microbiology of Farmyard Manure in Soil. 1 -- Changes in the Micro-flora and their Relation to Nitrification,' Journ. of Agric. Science, 21, 1931, p. 38.
Russell, E. J. and Richards, E. H. -- 'The Changes taking Place during the Storage of Farmyard Manure,' Journ. of Agric. Science, 8, 1917, p. 95.
Viljoen, J. A., Fred, E. B. and Peterson, W. H. -- 'The Fermentation of Cellulose by Thermophilic Bacteria,' Journ. of Agric. Science, 16, 1926, p. 1.
Voelcker, J. A. -- Report on the Improvement of Indian Agriculture, London, 1893.
Waksman, S. A -- 'The Influence of Micro-organisms upon the Carbon-Nitrogen Ratio in the Soil,' Journ. of Agric. Science, 14, 1924, p. 535.
Waksman, S. A. and Tenney, F. Q. -- 'Composition of Natural Organic Materials and their Decomposition in Soil. IV -- The Nature and Rapidity of the various Organic Complexes in different Plant Materials under Aerobic Conditions,' Soil Science, 28, 1929, p. 55.
Waksman, S. A. and Diehm, R. A. -- 'Chemical and Microbiological Principles underlying the Transformation of Organic Matter in Stable Manure in the Soil,' Journ. of the American Soc. of Agronomy, 21, 1929, p. 795.
Waksman, S. A. and Gerretsen, F. C. -- 'Influence of Temperature and Moisture upon the Nature and Extent of Decomposition of Plant Residues by Micro-organisms,' Ecology, 12, 1931, p. 33.
Whiting, A. L. and Schoonover, W. R. -- 'The Comparative Rate of Decomposition of green and cured Clover Tops in Soil,' Soil Science, 9, 1920, p.137.
Next: 6. Application to Other Areas
Back to Contents
To Albert Howard review and index
Back to Small Farms Library index
Community development | Rural development
City farms | Organic gardening | Composting | Small farms | Biofuel | Solar box cookers
Trees, soil and water | Seeds of the world | Appropriate technology | Project vehicles
Home | What people are saying about us | About Handmade Projects
Projects | Internet | Schools projects | Sitemap | Site Search | Donations | Contact us
