Abstract
During the Collaborative Study of Cassava in Africa (COSCA) survey, cassava yields and soil samples were obtained from farmers' fields in order to assess the yield levels and the contributions of soil properties to variations in such yield parameters as fresh root and shoot, harvest index and stand density. The average root yield was estimated as 10.5 t/ha, harvest index averaged about 0.50 and stand density was about 64,000 per hectare. Both the root and stand density had coefficients of variation above 150%. Each of the yield parameters correlated with at least 13 of the 28 soil properties considered in the simple correlation analysis carried out. The variations in the yield parameters were attributed to the differences in such agro-ecological factors as climate, altitude and soil properties. The contribution of soil variables to the variations in all the yield parameters was more than 80% in all cases. The most important variables were N:P ratio for root yield, clay content for shoot yield, OM content for harvest index and exchangeable Mn for stand density. This analysis indicates that in relating root yield to nutrient levels, nutrient ratios should also be considered because the absolute values of each nutrient may not be the only determining factor.
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