Improving agronomic efficiency in cassava- based farming systems in the Democratic Republic of Congo using organic and inorganic inputs

Cassava is an important food crop in small-holder farming systems in DR. Congo. Due to the limited use of organic and inorganic inputs, soil fertility becomes a major problem in cassava production systems. Inorganic inputs for small-holder farmers are often too expensive to apply at optimal rates and combining use of organic and inorganic fertilizer inputs is a suitable management principle for small-holder farmers. A study involving 15 households was carried out in DR. Congo with the following objectives: (ii) to determine the effect of an improved variety and fertilizer on agronomic efficiency in cassava or groundnut monocropping, (iii) to establish the effect of the combined use of inorganic and organic inputs on fertilizer response in cassava intercropping and (iv) to evaluate the influence of agronomic practices on the productivity of cassava-legume intercrops. Field trials were conducted to determine the use of improved variety and fertilizers at different rates on agronomic efficiency in the pure cassava or groundnut, the effect of combined application of inorganic and Chromolaena inputs, the effect of three legumes on yields in the cassava intercrops, the optimal cowpea spacing in the cassava-cowpea intercrop and the optimal cassava planting time in the cassava-groundnut intercrop in the two study sites. Data on rainfall, biomass, grain and root yields were collected. Significance differences between yields and varieties or soil types were tested using univariate analysis of variance. The CROSSTAB procedure using Pearson Chi Square analysis was used to test for significance effects of varieties on yields and farmer fertility score within site. Yield data were subjected to ANOVA and means separated using LSD (P < 0.05). Different soil types did not influence cassava root yields while different cassava varieties influenced cassava root yield in all surveyed sites. The use of improved variety and fertilizer application significantly (P = 0.017 and P = 0.016) increased crop yields by 48 to 173% and 58 to 156%, respectively over the control in both pure cassava and groundnut in both sites. Sole NPK, sole Chromolaena or combined use of NPK and Chromolaena significantly (P = 0.013, P = 0.003 and P = 0.03) increased casssava yields by about 45%, 43% and 77%, respectively relative to the controls in both sites. Cassava intercropping with soybean or cowpea was significantly (P < 0.001) superior over the pure cassava in terms of cassava tubert yield and the net benefits in both sites. Closer intra-row spacing of cowpea (30 cm) significantly (P =0.02) increased the net benefits by about 101% over the wider spacing (50 or 70 cm). Cassava planted 3 weeks after the groundnuts significantly (P = 0.042) decreased cassava tuber yields by 48 to 60% relative to cassava planted at the same time as groundnut. The results of this study showed that farmers should use an improved variety and apply fertilizer to improve the cassava and groundnut monocropping systems. Sole fertilizer or Chromolaena and the combined use of fertilizer and Chromolaena increased the yields and profitability of a cassava-groundnut intercrop. Cassava intercropped with soybean or cowpea has benefits in the cassava intercropping systems. The closer spacing (30 cm) of cowpea gave a higher income than the wider spacing (50 or 70 cm) in a cassava-cowpea intercrop. Cassava should be intercropped with groundnut within 2 weeks after sowing of groundnut. This study recommended that to improve cassava-based production systems, famers should use improved varieties and apply both organic and inorganic fertilizer, legume intercrop, space and plant at times when optimum yields are obtained as per the findings of this study.
Doctor of Philosophy Degree in the School of Environmental Studies, 172p. July, 2014