Assessing the Effectiveness of Supplementary Irrigation and Soil Conservation Techniques on Maize in Cyili Sub-catchment, Rwanda

Abstract

Limited natural water resource and unpredictable rainfall are challenges to agricultural production in East Africa. Modeling surface runoff in agricultural catchment is essential for water management currently and in the future. A study was conducted in Cyili sub-catchment, Southern Province of Rwanda during the short rainy season from 15th September, 2016 to 20th February 2017 with the aim to assess the potential of supplementary irrigation using surface runoff generated from the Cyili catchment. The study assessed soil moisture variation and supplementary irrigation water requirement for maize during short rainy season by quantifying the runoff volume generated in Cyili sub-catchment. The soil water conservation methods assessed included; mulching, contour ridges and supplementary irrigation using harvested surface runoff. A multi-method experimental and modeling activity was used to achieve the research objectives. The experimental design consisted of three treatments of water conservation methods and rainfed as a control. These were replicated three times in completely randomized design (CRD). Data obtained were subjected to analysis of variance using Genstat 14th edition. Treatment mean differences were evaluated using least significant difference (LSD) at 5% level of significance. Relationships between grain yield and yield components under water conservation methods were analysed using Minitab software version 17. Twelves soil samples were taken at a depth of 0-30cm and 30-60cm depth in the top, middle and bottom of the catchment. Soil moisture was determined by Gravimetric method. Supplementary irrigation water requirement was estimated using CROPWAT model version 8. Surface runoff volume was estimated using Soil Conservation Service-Curve Number method and ArcGIS version 10.1 x Results revealed that soil moisture variation in the subsoil was significantly (p ≤0.05) higher than the topsoil 4.81±4.08% and 3.54±1.77% (mean±SD), respectively. Results from the kriging method revealed that the soil moisture distribution for both soil layers were low in the lower and high in the upper part of the sub-catchment. Supplementary irrigation water requirement in the cropping season A (October to January) was 127mm (1,270m3/ha/season) with an application efficiency of 70% and translating to the entire catchment area (430ha) requirement of 546,100m3/season. The seasonal surface runoff volume was 300.85mm (3008.5m3/ha/season). The maize grain yield and yield components such as plant height, cob diameter and length, number of leaves per plant, 100grains weight, yield per plant were significantly (P≤0.001) affected by water conservation methods except the germination rate was not significant (p>0.05). Supplementary irrigation treatment significantly increased maize yield production at 11,982kg/ha compare to other water conservation methods (mulching, ridge and rainfed). This was followed by mulching significantly increased to 8,089 kg/ha compared to the rainfed treatment (control). Ridges produced 5, 937 kg/ha, and was not significant compared to the rainfed treatment with no additional treatment yielded 4,755 kg/ha of maize. Based on Pearson’s correlation coefficients, grain yield and yield components were positive and statistically significant (p≤0.001) under various water conservation methods. Based on these results, mulching and supplementary irrigation using harvested runoff can be regarded the potential option for increasing maize yields to stabilize food production under rainfall deficit agro-ecological conditions in Rwanda and other parts of sub-sahara Africa.