|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Indian experience with treated straw as feed|
Straw is a major by-product of crop production in the world. It is potentially useful as a source of energy, though it also contains worthwhile amounts of plant nutrients. Being bulky, it must, for the most part, be processed on the farm where it is produced. Ploughing it under or composting it are efficient wads of recycling plant nutrients, but these methods waste all of the energy the straw contains. In India virtually all straw is put through a two-stage process that both taps some of its energy and recycles plant nutrients. This process consists of feeding the straw to livestock and then using the dung as fuel. Usually, the dung is dried and burned directly, but this is undesirable because nitrogen is lost. A significant improvement is the introduction of the biogas plant to produce fuel gas from the dung; nitrogen is recovered from the slurry after fermentation (1 - 3). The efficiency of this two-stage, feed-fuel system ranges from 9 to 14 per cent (Annex 1).
Aside from purely energy considerations, the Indian system of processing straw on the farm has much to commend it. The relative simplicity of using an animal to convert straw energy to draught power is perhaps foremost. The same applies to milk production, a process in which straw provides the energy for the bioconversion of low-quality, inedible plant proteins (miscellaneous vegetation, grain-and oilseed-milling offals) into high-quality milk protein; the gain is not simply in proportion to the energy converted. Finally, it may be noted that straw cannot be used as a fuel in villages unless it is first passed through an animal; even present-day biogas plants cannot handle straw directly.
The efficiency of the livestock feed step can be increased by treating the straw before it is fed. The data presented in this paper indicate that the live weight gain in growing animals can be increased substantially if the straw is treated. The overall energy recovery from straw might not increase as a result of straw treatment because the more complete digestion of the treated straw by the animal would leave relatively less dung for use as fuel. Milk is, however, a more valuable form of energy than fuel.
The purpose of this paper is to review the Indian experience with various methods of straw treatment. It will include a discussion of the improvements obtained in animal productivity, the economics of such treatment, as well as the larger considerations of its energy cost and environmental impact. A special point made in this paper is that straw treatment techniques, like any new farming practice, will have to be evaluated on small private farms; satisfactory testing in an experiment station is not possible. A procedure for farm testing is outlined.