|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|A continuous composting system for disposal and utilization of animal wastes at the village level|
Never in the history of agriculture has soil fertility been considered as much as today. However, there is almost no literature on the subject, and no definite conclusions about how organic matter such as manure compost affects the fertility of soil. Nevertheless, a tremendous amount of manure is used on farm land.
The reason for the recent interest in soil fertility was the observation that crops grew abnormally and yields were highly variable when the amount of organic substances used for farming decreased and began to be replaced by chemical fertilizer. Why this is so is not clear. However, in one intensive vegetable cultivation area, farmers improved both quantity and quality of their crops when they applied organic matter to the soil.
The rapid economic expansion during the 1960s in Japan turned conventional agriculture into an enterprise, with the result that farmers were forced into raising either vegetable crops or cattle. This caused a shortage of organic fertilizer for vegetable farmers on the one hand, and created a serious problem of manure disposal for cattlemen. Subsequently it was found that application of cattle manure to soil improved its fertility significantly, even though it was originally considered as a source of nutrients for plants rather than as a component for maintaining soil texture. Thus, it appears likely that an agricultural system that depends on the heavy use of chemical fertilizer has a deleterious effect on soil fertility. The present paper summarizes the results from 13 years of studies beginning in 1964, to establish a system for using cattle manure as a valuable organic fertilizer for farm land.
The study was begun without any prior assessment of the impact of large-scale cattle raising, which it was thought would be common in the future. Furthermore, animal waste management was the main interest, and only scant attention was paid to the use of this valuable resource. For management purposes, it is mechanically easier to handle waste if large quantitites of excretions are mixed without separating solids from liquid. However, this method causes severe problems both from the standpoint of handling waste and using it. For one thing, only 50 per cent of solid waste was obtained when solids and liquids were mixed. Accordingly, the need was to develop an efficient system to separate solid matter from liquid waste, and this was accomplished by means of a screw press. Moreover, water-soluble organic matter, which has a high biological oxygen demand (BOD), remained in the liquid. The result of this study clearly indicated that the problem was due to the presence of soluble solids and the BOD of the raw faeces, and that the samples used for screw press treatment would have a high content of solids and a high BOD.
We have tested other systems, such as the centrifuge and rotary screen, for comparison with the screw press method, and found that solid matter isolated by the screw press is best for rapid manure composting. The conclusion is that the screw press method should be used on large-scale hog farms having several thousand animals. The best results are obtained when raw faeces are removed separately from the hog pen and the remaining, mixed excrete are partitioned by the screw press. It is not as efficient to separate total excretions by the screw press without any prior separation. The amount of faeces that can be preseparated from the hog pen is about 80 - 90 per cent of the total, and subsequent treatment of the remaining mixture of 10 - 20 per cent of faeces and urine by the screw press ensures that all solid wastes are preserved for composting. This method is ideal for large-scale hog raising, because it reduces costs of both waste management and pollution control.
Although most farmers still have a water pollution problem because they do not preseparate faeces, the screw press is becoming popular in Japan. About 400 such presses are now in use. One possible explanation for the wide farmer support of the screw press is that it provides fertilizer for the fields and improves soil fertility and crop production.
The main problem associated with the screw press system is handling of the raw faeces removed directly from the hog pen. Bad odour and high water content, together with psychological aversion, prevents some farmers from pre-separating faeces from liquid wastes.
In order to ameliorate this problem, we have tried heat-drying of raw faeces. Because cow and hog manures contain more water than found in chicken manure, more fuel is consumed if a conventional chicken faeces dryer is used. In addition, the quality of cow or hog manure in terms of soil fertility is inferior to that of chicken manure, so that in the long run, costs increased disproportionately.
Another approach is semi-drying of manure. This process was first developed mainly to reduce fuel consumption, but an additional advantage is that manure so treated can be composted fairly rapidly. Usually, high water content in the raw faeces and solid fractions remaining after mechanical separation of excrete precluded rapid composting. It is now understood that reducing the water content of faeces from 80 - 85 per cent to 60 - 65 per cent is the key process in making good compost. Rice straws and leaves can be used to absorb water during composting.
The continuous process of composting animal faeces, i.e., semi-drying by heat, composting, mixing with raw faeces, and re-composting, was tested on a small scale for evaluation of the process. Although no large-scale study was done, the process was considered to be quite promising, and use of the method began to spread in the country beginning in 1970.
Unfortunately, mixing the compost with raw faeces was thought to be too labour-consuming, so widespread use of the continuous composting system did not take place until Tsuneo Jimbo developed a loading system in 1973. This success stimulated Shuichi Anzai to develop a so-called "pile-up system," which consisted of loading raw faeces on top of the compost so that mixing is required only on the top portion.
This development not only means that the middle-sized farmer can continuously make compost from manure but also allows centralized composting at the village level. The process is now popular all over the country.
The carbon ratio of raw cow manure is about 15:25, that of hog manure 10:13, and of chicken manure, less than 10. The carbon ratio of solid fractions after mechanical separation of excrete is 30 in cow dung and 17 for hog manure. These values are quite different from those in rice straw, which has a ratio of 70:80 due to the high content of lignin. Raw faeces have an equal or lower carbon ratio compared to well-matured compost or manure compost. If one judges the maturity of compost by its carbon ratio, raw faeces have a value close to that of fully matured manure compost, and thus is satisfactory.
However, when the water content of raw faeces or solid isolate was reduced to 60-65 per cent, rapid fermentation was usually observed. One possible explanation of such active fermentation is that manure usually contains many biodegradable substances, such as shortcarbon-chain fatty acids. In addition, manure is also high in nitrogen, thus making a good substrate for microorganisms. The temperature profile increased significantly at the beginning of fermentation and fell after the first few days during composting, supporting the idea that the time required for composting raw faeces is much shorter than that observed during conventional manure composting. The reason is believed to be that raw faeces are much more susceptible to attack by micro-organisms.
Compost from either raw faeces or solid isolate is generally rich not only in organic materials but also in various minerals that help to enrich soil. In particular, the compost made by fermentation at high temperature did not decompose rapidly in the soil, which lessens the hazard of gas production that has been observed when immature compost is applied.
Raw faeces could become an ideal organic resource if a system is developed to remove water content economically without just mixing in rice straws, etc. Compost from raw faeces has been proved, not only by small-scale tests, but also by practical use, to be a good fertilizer as well as a soil conditioner. Although it is difficult to detect a significant change in the physico-chemical properties of soil by adding compost at a level of 1 - 2 tons per year per 10 acres (it is generally said that 5 tons per year are essential to change soil conditions), a significant improvement in crop growth has been observed when compost was used compared with results from application of chemical fertilizer. For example, in vegetable production, manure compost used alone led to a good yield of high-quality vegetables and met more than 60 - 70 per cent of total nutrient requirements of the crops.
It is particularly interesting to note that unlike chemical fertilizer even a small amount of organic matter improved acid soil in a vegetable field.
Cattle manure is particularly beneficial in volcanic ash soil. On the other hand, application of organic matter to a paddy field is valuable under the right soil conditions. In certain instances, reduced rice yields were observed, implying that the method used for adding raw faeces is very important. They should be applied to the paddy field as early as possible to allow enough time for decomposition before the rice is planted, to prevent any drop in pH value of the soil. If this is done, the effect of organic matter has a detectable benefit, even in a rice paddy with peat in its lower layer.
Raw cow, hog, and chicken manures have been tested in direct application to the field using 200 tons per 10 acres of each kind of manure. Micro-organism activity peaked four to seven days after application, and then dropped quickly. This phenomenon correlates with the process of composting raw faeces. The increase in micro-organism activity at the initial phase is due to the higher BOD of the faeces, and the BOD and CO2 gas production have shown a good correlation.
An unusual increase in microbial activity in soil will affect the crops adversely, particularly right after planting. Care should be taken to avoid these undesirable effects when raw faeces are going to be used. A large quantity of raw faeces applied to soils maintained good productivity of vegetables without further addition of fertilizer for four years, which means that raw manure is slow-acting and effective for long periods. Chicken manure, which showed a very high microbial activity at the initial phase, became less effective much faster than either cow or hog manure in terms of crop productivity. This result indicates that chicken manure has less residual activity and soil-conditioning power than the other manures.
Mixing raw faeces with soil will heighten the rate of faecal decomposition because good aeration is permitted by increased surface contact between faeces and soil.
The problem with the present method is that the amount applied to the field is far beyond the quantity required by the plants. Such large-quantity application of raw manure will certainly have an undesirable effect, particularly with regard to pollution of the environment. For example, part of the nitrogen in raw faeces may diffuse into the soil during decomposition. It is interesting to note that denitrification has been observed when raw faeces, rich in organic nitrogen, have been applied, while with application of inorganic nitrogen, no denitrification has been detected. This phenomenon indicates that, when organic nitrogen is applied in large quantities, part of the nitrogen is denitrified by the activity of micro-organisms. I believe that this sort of microbial regulation, such as conversion of excess organic nitrogen to an inert form, is very important and further study of the interrelationships between organisms and their environment is essential.
A more detailed description of the foregoing discussion can be found in my article in the Bulletin of the Agricultural Research Institute of Kanagawa Prefecture, No. 1 18, "Studies on the Utilization of Animal Wastes in Agriculture," 1977.