Modelling surface runoff using the soil conservation service-curve number method in a drought prone agro-ecological zone in Rwanda

Runoff farming is reported to improve land productivity and crop yields in hot and dry climates. This study was conducted to assess the available rainwater that can be harvested in a conserved catchment in a drought prone agro-ecological zone. The study was carried out in the Cyili sub-catchment, southern province of Rwanda, which has an irregular rainfall pattern and unexploited runoff water. Soil Conservation Service-Curve Number method (SCS-CN), CROPWAT model version 8 and Hazen model with an average daily rainfall data recorded from 1971 to 2016 were applied to estimate the runoff and water requirements in the study area. Findings of the study revealed that more than half rainfall water received in the catchment was lost through runoff (229.8 mm) and effective rainfall was lower (246.9 mm) than the actual crop water requirement for maize (330 mm). The expected seasonal surface runoff volume to be harvested by the farmers was 3008 m3 ha−1 per season and 1.29 × 106 m3 per season for the entire whole sub-catchment (430 ha). Based on Hazen model, the return period of low rainfall (dry spell) event would be expected every 2 years with a 98% probability of occurrence. Cyili sub-catchment has higher potential runoff volume to stabilize the deficit of water demand in the period of short rainy season. This suggests that rainwater harvesting through supplementary irrigation is an option to improve the crop yield in the dry period as well as in the annual dry season. Keywords: Available rainwater, Cyili sub-Catchment, Curve number, Runoff, Rwand

Data from: Wheat nutrient response functions for the East Africa highlands

Wheat (Triticum æstivum L.) is an important East Africa highland crop but yields are low. Information is scarce for optimization of fertilizer use. Research was conducted to determine yield response functions for N, P and K, and to diagnose Mg–S–Zn–B deficiencies. The average grain yield increase in Rwanda due to N application was 1.5 Mg ha−1 with a mean economically optimal rate (EOR) of 68 kg ha−1 N. In Kenya and Tanzania, yield was increased by 29% with EOR N for two SY but unaffected by N rate for four other SY which on average had 50% of the soil organic C (SOC) as the N-responsive SY. Yield was increased, on average, with application of P and K by 0.47 and 0.23 Mg ha−1, respectively, at EOR in Rwanda but effects were inconsistent for other SY where soil test K was higher than in Rwanda. Application of Mg–S–Zn–B resulted in 0.46 Mg ha−1 more yield in Rwanda but did not affect yield at other SY where the average soil test values for these nutrients was 35% higher than in Rwanda. If the financially constrained farmer opts to apply the affordable fertilizer to twice as much land at 50% EOR compared with 100% EOR, the mean yield increase is reduced by 27% but production and PCR are increased by 43 and 72%, respectively. Nutrient effects were relatively consistent and positive in Rwanda, but less and less inconsistent elsewhere with generally less SOC, more K–Mg–S–Zn–B availability, and often lower yields