Capper: In recent years an enormous amount of research has been conducted on chemical treatment of crop residues but, as Drs McDowell and Nordblom have indicated, there has been disappointingly little uptake of the technology by farmers. Yet scientists continue to produce numerous publications on chemical treatment, neglecting the potential to exploit natural variation in nutritive value.
McDowell: The project I was involved with in India found that shortage of labour and storage space were major constraints. While researchers were present the project went well but when farmers were left to continue on their own initiative, the process broke down.
Van Soest: At Cornell we have analysed around 200 treated residues and have been impressed by the variability. Some materials actually decreased in value as a result of moulding or side reactions producing indigestible products. Urea treatment has very little effect on lignification. It causes swelling but intake is not increased.
Thomson: In North Africa and West Asia, ICARDA's mandate region, there is a deficit of crude protein in the feed resources. It would seem appropriate therefore to continue to look to urea as a source of protein supplementation.
Reed: There is a need for a clearer distinction between urea supplementation and treatment. In experiments conducted in the Ethiopian highlands urea treatment resulted in very little improvement in animal response.
Onim: The storage of crop residues and protection from weather and pests such as termites may be difficult for the farmer. On more intensive small holdings in Kenya, for example, storage of crop residues may compete or space with threshing and living accommodation.
Ørskov: In many parts of Asia the situation is different, in that there are communal threshing grounds and crop residues are frequently stored nearby.
Nordblom: In ICARDA's mandate region the prices of grain from crops such as wheat and lentils are controlled by governments. This means that farmers often derive a large part of their income from the sale of crop residues. An example can be given from Egypt where farmers rejected a high grain yielding variety because of its inferior straw quality.
Capper: If government grain prices were adjusted to import/export parity prices what would have been the reaction of farmers to high grain yielding varieties with lowered straw quality?
Nordblom: I think their reaction would have been the same, i.e. they would have continued planting traditional varieties.
Ørskov: Artificially low feed concentrate prices in Egypt may distort the demand for crop residues and therefore their prices relative to grain.
McDowell: Farmer evaluation of the utility of crop residues is affected by the desire to maximise total income. The use of external resources such as feed concentrates together with residues produced on farm may result in a better overall utilisation of farm resources.
Ørskov: Animals have to live with fluctuating feed resources and a fluctuating output of products. The animal may provide the required flexibility by storing fat to be used for productive purposes at a later stage. Has Professor McDowell worked out how to use animal flexibillity as an alternative to providing better quality feed?
McDowell: Crop residues can only provide maintenance level nutrition. Thus any further deterioration in their nutritive value will reduce animal production. For instance, farmers in Mexico were growing traditional varieties with crop residue digestibilities of between 52 and 62%. CIMMYT varieties currently being released have crop residue digestibilities of less than 50%. A major factor causing this is a lower ratio of leaf to stem. The digestibility can only be restored to its former level by sodium hydroxide treatment, which is costly.
Nordblom: It may not be necessary for farmers to feed a balanced diet over all seasons. It may be to the farmers' advantage to allow their livestock to lose weight when feed is poor and in short supply and to exhibit compensatory growth when feed is plentiful.
Fussell: In West Africa, millet is grown in mixtures with legumes in a mixed cropping system. As a result the residues available are a mixture of stover and legume straw. The protein content of the latter improves overall feed value.
Pearce: I would like to caution against regarding urea as a cure for all problems of N deficiency. Considerable skill is required to optimise responses and it may be asking too much of a smallholder to achieve this. Supplementary energy and minerals are required in many circumstances to derive benefits from urea supplementation.
Witcombe: The multipliers used by Nordblom and Kossila for sorghum and millets to convert from grain yields to yields of crop residues differ and it appears that the latter are overestimates.
Nordblom: The figures I gave were for the amount of stover available.
Witcombe: I consider that the multipliers should be 4 for Africa and 3 for India.
