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Low inherent soil fertility in the highly weathered and leached soils largely accounts for low and unsustained crop yields in most African countries. But in particular, the major nutrients, nitrogen (N) and phosphorus (P), are commonly deficient in these soils. This scenario of nutrient depletion is reflected in food deficits and hence the food aid received continuously, specifically in sub-Saharan Africa. Undoubtedly, substantial efforts have been made in the continent to replenish the fertility of degraded soils in attempts to raise crop yields, towards self-sufficiency and export. Such efforts consist of applications of both organic and inorganic resources to improve the nutrient status of soils and enhanced nutrient uptake by crops, provided that soil moisture is adequate. Overall, positive crop responses to these materials have been obtained. Thus in the East African region, maize (staple) yields have been raised in one growing season from below 0.5 t/ha without nutrient inputs, to 3-5 t/ha from various nutrient amendments at the smallhold farm level. However, in spite of the positive crop responses to nutrient inputs, farmers are generally slow to adopt the soil fertility management technologies. In this paper we review the impact of some technologies, focussing the use of nutrient resources of different characteristics (qualities) in relation to improved crop yields, with an overall goal to enhance technology adoption. Thus, inorganic resources or fertilizers often give immediate crop responses, but their use or adoption is rather restricted to large-scale farmers who can afford to buy these materials. Organic resources, which include crop residues, water hyacinth and agroforestry shrubs and trees, are widely distributed, but they are generally of low quality, reflecting the need to apply large quantities to meet crop nutrient demands. Moreover, most organics will add N mainly to soils. On the other hand, phosphate rocks of varying reactivity are found widely in Africa and are refined elsewhere to supply soluble P sources. The recently developed soil fertility management options in East Africa have targeted the efficient use of N and P by crops and the integrated nutrient management approach. Some people have also felt that the repackaging of inputs in small, affordable quantities, such as the PREP-PAC described in this paper, may be an avenue to attract smallhold farmers to use nutrient inputs. Nonetheless, crop responses to nutrient inputs vary widely within and across agroecozones (AEZs), suggesting specificity in recommendations. We highlight this observation in a case study whereby eight soil fertility management options, developed independently, are being tested side-

Sorghum (Sorghum bicolor L. Moench) is one of the important cereal crops utilized worldwide for human food, animal feed and to a lesser extent as a raw material in commercial food industries. The crop is a strategic commodity for food security, particularly in harsh environments. In Kenya, sorghum is an important crop consumed in some parts of the country as a staple food. It is also a major source of income to small-scale farmers who are its major growers. In the past, its cultivation was concentrated in the medium and low altitude areas of Kenya. However, with the increase in improved varieties, sorghum cultivation has spread to the cold semi-arid highlands. Sorghum production in Bomet District of Kenya is low. Agronomic, socioeconomic and varietal constraints usually affect the production of sorghum. In this study, it was assumed that use of low quality seed was among the factors leading to the low productivity of sorghum in Bomet District. Therefore, a survey was carried out in Bomet District of Kenya with the objective of identifying the constraints to onfarm sorghum seed production. A total of 100 farmers were interviewed using structured questionnaires. The survey focused on a wide range of seed management issues. From the descriptive analysis it was concluded that sorghum grain yield obtained by farmers in the previous season were low as compared to the documented research sorghum yield potential. The major constraints to on-farm sorghum seed production included poor seed source; lack of socioeconomic resources; poor crop husbandry; poor post-harvest handling of seed; damage by weeds, pests and diseases; and lack of marketing incentives. Regression analysis showed that only sorghum farm size (as partitioned by farmers) significantly (P≤0.05) affected sorghum grain yield in the district. Therefore, there is need to have high yielding varieties which will compensate for the ever diminishing farm sizes and land subdivision. In addition, there is need to assess the quality of sorghum seeds planted by farmers to determine the effect of such seeds on sorghum production. There is also need to improve the farmers' agronomic practices on sorghum production especially in relation to fertilizer application. An economic analysis to find out the profitability of purchasing inputs in sorghum production is required. An investigation on pests and diseases affecting sorghum production is also needed. Finally, extension services should be given to farmers and the prices of farm inputs subsidized.

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