EFFECTS OF INORGANIC AND ORGANIC FERTILIZERS ON NUTRIENT UPTAKE, SOIL CHEMICAL PROPERTIES AND CROP PERFORMANCE IN MAIZE BASED CROPPING SYSTEMS IN EASTERN PROVINCE OF RWANDA

The Eastern province of Rwanda is highly populated. This has led to continuous cropping systems without addition of external fertilizers to compensate losses due to removal of grains and residues through harvesting. In such conditions, soil fertility decline is a major factor limiting per capita crop production in the area. It is quite difficult for smallholder farmers to afford to buy and apply adequate quantities of mineral fertilizers and organic sources, making it difficult for them to replenish the soil fertility. In order to address this problem, experiments were laid out in farmer fields in the Eastern province of Rwanda in an incomplete randomised block design with 14 treatments. The objectives were to evaluate the response of maize, common bean and soybean to combined application of mineral fertilizers and FYM on yields, BNF, N balance, and soil chemical properties; their rotational effect on the subsequent maize; and to economically analyse their fitness to adoption by means of the BCR and MRR analyses. Fertilization treatments were 5 t of FYM ha -1 , 200 kg of DAP ha -1 , and 2.5 t of FYM + 100 kg of DAP ha -1 (1⁄2 DAP + 1⁄2 FYM). Two intercropping systems, MBILI (2:2 common bean: maize) and 2:1 (common bean: maize) were compared 1⁄2 DAP + 1⁄2 FYM significantly (P = 0.05) increased the yield of common bean, soybean, and maize and improved their fertilizer agronomic efficiency of DAP both in short and long rains. Intercrops had the LER > 1.0. The BNF was significantly higher (P = 0.05) in common bean plots than in soybean plot. N balances were more negative in soybean than in common bean treatments (P 1.18. Farmers’ evaluation was positively correlated between male and female farmers (r = 0.671 at P < 0.001 in short rains, and r = 1 at P < 0.001 in long rains) and was negatively correlated to the BCR and MRR. From this study, mineral fertilizers should not be applied to common bean and soybean in rotation because they do not improve their BNF and yet, these crops are not responsive to them, hence a loss of investment. FYM or 1⁄2 DAP + 1⁄2 FYM should be applied to maize planted in rotation (responsive and economically acceptable). Intercropping common bean and maize in 2:1 rows arrangement is also economically feasible. Rotation of common bean or soybean with maize is recommended.