Composting

It is increasingly important to step up and encourage the use of organic fertilizers in tropical agriculture because of the problems the use of chemical fertilizers presents to developing countries. For farmers in ACP countries chemical fertilizers are often too expensive, and increase the dependency of both farmers and countries on imports, either because they are imported as finished products, or because the energy required to produce them is imported. As a result, in some countries, farmers are forced to devote practically all their working efforts to paying off debts incurred in the purchase of fertilizers. When rain does not arrive or water is scarce, fertilizer pellets do not dissolve properly and can 'burn' the crops, while in humid zones much of the nutrients can be washed away by torrential rain. Chemicals can also kill beneficial micro-organisms in the soil. Plants which have received heavy applicahons of nitrogen through the use of chemical ferhlizers may suffer from increased susceptibility to pest infestation. Farmers then resort to further chemicals in the form of pesticides, with all the undesirable economic and ecological consequences. In contrast, organic fertilizers not only bring the necessary nutrients to the soil, but also improve its condihon and, above all, its ability to retain moisture. Compost is a form of organic fertilizer which can be a solution to the problems mentioned above and yet is free of the difficulties that occur with the use of several other organic substances -smell, storage and pathogens. Composting is the process whereby vegetable matter is stacked into a heap or pit and allowed to ferment and rot through the action of micro-organisms. In the process of composting, organic wastes are decomposed, nutrients are released, and pathogens are destroyed. Compost protects and nourishes plants and soil and it reduces overall water requirements in areas where lack of water is the fundamental limitation on produchon. Compost is particularly useful for market gardening because it provides a source of nutrients which can be rapidly assimilated by plants. Furthermore, composting can be an excellent alternative to chemical fertilizers in areas where cultivation of a single crop has exhausted the soil. This is a common problem in Sahelian Africa where groundnuts have been grown extensively. The benefits of compost are many: many materials that are suitable for use as organic manure have a high carbon:nitrogen ratio when fresh. By composting they are partly mineralized, thus reducing the C:N ratio, which, in turn, facilitates the release of nitrogen. Also, during composhng temperatures may reach 60-70C, and most weed seeds and pathogens are consequently killed. In the tropics this can be one of the primary purposes of composting. Another advantage is that during decomposition, weight and mass are reduced, but not necessarily the nutrient content. The structure of the organic material also changes during the process, and the bulky mass is converted into a friable substance. When making compost, different materials may be combined to good effect. Residues with a high C:N ratio, such as rice straw, which on its own mineralizes very slowly, may be combined with material with a low C:N ratio, such as animal manure. This combinahon will ensure the correct rate of composhng. In Sudano-Sahelian Africa, the most common organic or vegetable substances used are dung, peanut oil, fish scraps and miscellaneous vegetable matter. Where composting is new to people, they have to learn about its benefits and the compost making process. The conditions for microbial growth in the compost heap must be as favourable as possible: there must be sufficient air; the heap must not be too dense; there must be sufficient moisture - but not too much (in arid areas the compost is often put in a hole in the ground to prevent dehydration); and there must not be too much light - so the heap should be made in the shade, under a roof or covered with a layer of straw or soil. In the Sahel there has been a structured attempt to encourage Senegalese farmers to make compost. The campaign is conducted by PRONAT (PROtection of NATure against the enemies of crops) team of ENDA (Organization for ENvironment and Development in Africa). Since 1983 they have held training sessions of two to three days for farmers to learn how compost can improve crop yields and soil fertility. The sessions are slide shows, given in Wolof either by research technicians from PRONAT or by farmers with practical experience who give 'hands-on' demonstrahons. After training, farmers return to their villages and pass on the knowledge gained to others in the local group. ENDA published a brochure in French and Wolof in 1985 on composting,which was well illustrated to help those with literacy difficulhes. In addition, CTA and Agromisa have produced one of their Agrodok booklets in English on the preparation and use of compost Politically speaking, the drive towards selfsufficiency in food produchon is a top priority in most developing countries, and teaching composting techniques should be high on the list of means to achieve this end. In the Sahel, for example, there are very fragile soils which have little resistance to the ravages of soil erosion by wind and water. Composting could help rebuild and fortify this fast-disappearing resource. References: Abou Thiam (Coordinator PRONAT) - Institute of Environmental Studies - University of nnknr - PO Box 3370 - Dakar- SENEGAL. Agromisa, 1981. The Preparation and Use of Compost - Agrodok 8 - PO Box 41 - 6700 AA Wageningen - THE NETHERLANDS ENDA, 1984. Une expe'rience de compostage villageois au Senegal oriental. -ENDA-TM BP3370- Dakar-SENEGAL.It is increasingly important to step up and encourage the use of organic fertilizers in tropical agriculture because of the problems the use of chemical fertilizers presents to developing countries. For farmers in ACP countries chemical fertilizers..