02211naa a2200157 a 450000100080000000500110000800800410001910000140006024500950007426000090016950000100017852016690018870000200185770000150187777301610189216373112009-02-19       2008    bl uuuu     u00u1 u    #d1 aNUTTI, M.  aInstitutionalizing the biofortification strategy in a sustainable waybthe case of Brazil.  c2008  aS1-2.  aWith worldwide escalating food prices and a growing demand for biofuels, it is vital to increase the productivity of cassava in Africa. With average cassava yields of 7.0 and 11.3 t/ha in Uganda and Kenya respectively, yield levels in East Africa are low, While differences in agro-ecology explained part of the variation between sites, monocropping, weed management and hiring labour contributed to higher yields within sites. The importance of good management practices (improved varieties, monocropping, proper plant spacing, timely planting) was confirmed by the higher yield levels - 10.4 and 14.2 t/ha in Kenya and Uganda respectively - obtained in farmer managed control plots in 99 on-farm trials. Abiotic factors were more important yield determining factors than biotic factors, while weed management also explained an important part of yield variability. Fertilizer use (100-50-100 N-P205-K20) increased cassava yields by 5.8 t/ha, above ground biomass by 9.0 t/ha and the number of storage roots per plant by 2.7, but did not affect harvest index or root dry matter content. Although cassava production was limited by different nutrient(s) across sites, combined NPK  fertilizer always resulted in the highest yields. Fetilizer response was related to soil fertility and early rainfall, but did not between varieties, across management levels or pest and disease pressures. On the short term, cassava productivity in East Africa can be improved by the widespread promotion of simple agronomic practices and improved varieties. On the longer term, fertilizer will be essential for the development of sustainable and profitable comercial cassava schemes.1 aCARVALHO, J. L.1 aFUKUDA, W.  tIn: SCIENTIFIC MEETING OF THE GLOBAL CASSAVA PARTNERSHIP, 1., 2008, Ghent. Cassava: meeting the challenges of the new millennium. Ghent:: IPBO, 2008. p. 26.