Resources and Conservation最新文献

Bangladesh has a tropical monsoon climate. The major climatic differences within the region concern the total rainfall. About 500 soil series have been recognized and in the local Bangladesh classification these are grouped into 17 general soil types. Organic matter is an important constituent of mineral and peat soils. Organic-matter content in soil is dependent on agro-climatic conditions and is difficult to conserve at a high level in tropical and subtropical conditions. Soils of Bangladesh are low in organic matter, and conserving and maintaining it at moderate levels is one of the serious problems in soil management. This may be accomplished through: maximum return of crop and animal residues to soil; balanced use of chemical fertilizers such as urea, triple superphosphate and muriate of potash; use of biofertilizers; green manuring in crop rotation; and proper utilization of farm manure, night soil, composts and nitrogenous organic materials, such as crushed bones, fish wastes, mustard, sesame, castor cakes, etc.

In the Taihu region of Jiangsu Province, organic wastes applied to soil, including straws of crops, human and domestic-animal feces, provided 805 kg/ha of soil organic matter in 1982, equivalent to about 43% of the total amount of soil organic matter decomposed each year. By using the organic wastes, the severe imbalance in the proportion of N, P and K fertilizers applied was improved. The possibility of raising the proportion of organic-matter recycling is discussed and some specific investigations needed in this respect are indicated.

Municipal wastewaters carry appreciable concentrations of nutrients which have a nuisance value if disposed of in surface waters. In contrast, conservation and proper utilization of these nutrients through wastewater recycling in a soil-plant system will not only augment manurial potential, but also will provide a mechanism for control of water pollution. The value of the nutrients in the wastewater in India is around Rs. 1752 million (US $140 million) per annum.

The application of wastewater to the land is a common practice in India. Relative concentrations of major plant nutrients, N, P and K in the wastewater are not properly balanced for crop requirements. Long-term field experiments at the National Environmental Engineering Research Institute (NEERI), Nagpur, India, have shown that the nitrogen contribution from wastewater irrigation is usually in excess of crop requirements, while phosphate is deficient. Dilution of sewage to reduce the contribution of nitrogen and the application of supplemental NPK through fertilizers provide balanced nutrition and improve crop yields. Appropriate dilution of sewage this way has been shown to increase nutrient utilization efficiency (yield of crop per kg of nutrient) and reduce the organic, inorganic and microbial load on the soil. This approach also makes it possible to extend the benefit of the fertilizing potential of wastewater to a larger area.

The potential of manure composting as a waste utilization and disposal option for animal waste has been evaluated on the basis of the operation of a pilot plant capable of handling 15 Mg animal manure daily. Animal manure mucked-out dry from livestock farms was subjected to high-rate composting processes which produced the mature product in less than two months. The composition and quality of the manure compost at various stages of operation were assessed. Results showed that the mature manure compost produced under controlled conditions is a stable and odour-free produce with a carbon:nitrogen ratio of about 15 and moisture content of about 50%. Field trials further demonstrated that the manure compost is suitable for use as a soil conditioner for landscaping, tree planting and market gardening applications. Cost comparison with other waste recycling and disposal alternatives indicated that manure composting is one of the most cost-effective options for dealing with animal waste.

The biotechnological exploitation of microbes is becoming more and more important both for industrial purposes and in the treatment and utilization of solid organic waste materials. Agricultural and industrial organic residues contain substantial amounts of cellulose and have the potential of serving as growth substrates for either ruminants or microorganisms. However, due to the intimate association of the cellulose with hemicellulose and lignin, the cellulose is not readily available as a carbon source unless the lignin component of the residues is modified or removed. Mushrooms can transform various solid organic wastes which are inedible by man into a highly valued food protein for direct human consumption. The biological efficiency ranges from 10 to 100%. The solid-state fermentation of lignocellulose-containing agricultural and forest wastes by white rot fungi results in a product which can be used as animal feed. The average rumen digestibility of decomposed wood is between 30 and 60%, as opposed to a maximum of 3% for undecomposed wood. After the mushrooms have been harvested, the spent compost, besides being rich in nitrogenous material, contains partly degraded lignocellulosic components. When this is combined with animal dung or human excreta in a biogas digester, it yields not only biogas but also a good quality soil conditioner. It is suggested that an integrated approach by means of microbial biotechnology for the production of mushrooms, feeding material, biogas and biofertilizer is a feasible approach for rural and urban solid-waste utilization and disposal.

A brief description of secondary sewage treatment in Hong Kong is given. Chemical analyses of the sludge produced by the major plants have indicated that the heavy-metal concentrations are relatively low and the fertilizer values are of the same order of those in the U.K. In the light of the U.K. guidelines regarding utilization of sludge on land, it has been concluded that sewage sludge can be utilized safely and economically in Hong Kong, most likely for landscaping and top soil where health risks are minimal.

In the past, farming has always managed to achieve a balance between the production of animal wastes and the demand for such wastes as manure for arable cultivation. Intensive farming upsets the balance either by overproduction of animal wastes or overdependence on artificial fertilizers. Animal rearing in the New Territories of Hong Kong is such an example where market demands for locally produced meat have led to intensive animal rearing without locally available means of beneficial reuse of the waste. Gross pollution of streams and coastal waters has resulted. The permanent solution must be to redress the balance between the two major types of agricultural activity.

The recycling of organic wastes for maintenance of soil quality and improved crop productivity is of economic importance. Composting is a microbiological, non-polluting and safe method for disposal and recycling of organic wastes by bioconversion to fertilizers. Efficient cellulolytic cultures, such as species of Aspergillus, Trichoderma, Penicillium and Trichurus, accelerate composting for efficient recycling of dry crop wastes with high C/N ratio and reduce the composting period by about one month. Enrichment of partially composted crop wastes can be achieved by Azotobacter and phosphate solubilizers to improve the nitrogen, available phosphorus and humus content of finished compost compared with controls. Amendment of the finished compost with 1% rock phosphate, and inoculation with nitrogen-fixing and phosphate-solubilizing bacteria, increased the nitrogen and humus content and decreased the C/N ratio of the compost. Blending of finished urban compost and fresh moist sludge, in a 2:1 proportion, and amendment with 1% rock phosphate, resulted in a compost rich in nitrogen with a C/N ratio less than 10. The composts prepared by improved techniques were found to increase the yields of crops.

Nepalese agriculture is still basically traditional and is characterized by small scattered holdings, poor farmers, rain-fed cultivation and unavailability of modern inputs due to poor transportation facilities. For a country like Nepal, where 68% of the area is covered by hilly and mountainous regions, recycling of agricultural wastes is one of the main sources of organic fertilizers which the marginal farmers can afford to produce and use to increase their crop production. Various techniques have been employed in order to improve the quality of these organic fertilizers. Compared with the theoretical need of organic matter and the quantities available through crop residues and livestock manure, the quantity which can be produced by composting of town refuse is very small.

Chicken manure is added to freshwater fish ponds as pond fertilizer and supplementary feed in Hong Kong as well as in other Asian and East European countries. The present study was undertaken to observe the morphological changes in the gills of tilapia treated with chicken manure using scanning and transmission electron microscopy. Tilapia, Sarotherodon mossambicus, were fed chicken manure as a supplementary diet for four weeks under laboratory conditions. This produced a swelling of the gill epithelium and enlargement of the sub-epithelial space in nearly all the lamellae of the fish gill. Cell junctions, i.e., desmosomes, were disrupted with separation of adjacent epithelial cells in the severely damaged fish gills leading to the exposure of the underlying basement membrane and the capillary endothelium to the water. Such damage of the wate—blood barrier of the fish gill will impair the respiratory function of the fish.