Seed biochemical composition was the basis for segregating 24 crops into four distinct groups. Nitrogen requirements of pulses and soybeans were so great that sustained seed growth demanded continued nitrogen translocation from vegetative tissues. This translocation must eventually induce senescence in these tissues, restrict the duration of the seed-fill period, and limit seed yield.

Programs to develop the traditional livestock farming of the Sahel have often been ineffective despite great human and financial contributions. Efforts directed at better pasture and herd management, pasture improvement. livestock fattening, and increased marketing, have failed to improve the overall productivity of the herds and to stop range deterioration. A major reason is that many of ophy that the problems have to be solved primarily by preventing overgrazing, since at present the climate cannot be influenced and irrigation can only be used locally. Smaller herds and the development of areas of nonuse (wells). in addition to improvement of the herd composition and animal health, will improve the output of livestock farming. Future good management of the rangeSummary. Results of a Malian-Dutch research project on the Sahelian pastures and their utilization suggest reasons why some efforts to develop traditional livestock farming in this area have been unsuccessful. Failure to appreciate the effects of low soil fertility as well as low rainfall on pasture production has tesulted in underestimation of the productivity of the nomadic and semi nomadic livestock farming system and overestimation of the possibilities for increasing production by better management and by modernization.

Soybeans are hypothesized to be “self‐destructive” since they apparently need to translocate large amounts of nitrogen from vegetative tissues during seed‐fill to sustain seed growth. To assess the possible limitations of this characteristic on soybean seed yield, a simple, dynamic simulation model is developed which accounts for the availability of nitrogen and photosynthate within the plant. The simulations show that the duration of seedfill and seed yield is clearly limited by the self‐destructive characteristic. Increased availability of nitrogen within the plant is required for significant increases in soybean yields. Possible alterations of the model required to mimic actual soybean seed growth are presented.

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