Performance and Water Productivity of Selected Sweet Potato (Ipomoea Batatas L) Varieties Intercropped With Common Beans in Katumani - Kenya

Abstract

The main deterrent factors for achieving sustainable agricultural production in Eastern Kenya are irregular rainfall and low available water capacity. Knowledge on crop performance, water needs and optimization of deficit irrigation schedules would therefore help to minimize water stress and thus increase ASALs' achievable yields. The study was undertaken for two short rainy seasons of S(i); 2018 and S(ii) 2019, respectively at KALRO-research station in Katumani, Machakos County. The objectives were; to assess the performance, growth, yield and water use efficiencies of two sweet potato varieties in sole and intercrop systems as well as to predict the implications of climate change on sweet potato water needs and scheduling irrigation water using CROPWAT model version 8.0 from 2019 to 2039 based on a rainwater discrepancy. The trials were established as a Randomised Complete Block Design with three replications acting as blocks and five treatments comprising of: (i) V1; Kabode (orange-fleshed), (ii) V2; Bungoma (white-fleshed), (iii) B1; Sole common beans (Miezi miwili), (iv) V1M; Kabode + common beans and (v) V2M; Bungoma + common beans. Sweet potato was the main crop of interest. Intercropping with common beans significantly (p < 0.05) reduced the yields of Kabode and Bungoma varieties by 18.4 and 32.0 %, respectively. Sole cropping of Kabode variety yielded 31.4 t ha-1 significantly (p < 0.05) higher than monocropped Bungoma with 23.9 t ha-1 whereas, ones intercropped with common bean yielded 26.2 and 18.1 t ha-1 respectively. Similarly, the percentage of land saved by intercropping varied from 8 to 33%. Aridity Indices (AI) in seasons (i) and (ii) were 0.4 and 1.2, respectively and contributed to shortening and lengthening of the humid periods. The total and readily available water within the soil profile were 330.4 and 214.7 mm, respectively. In addition, data from the test crops showed water use efficiency values of 39.8 and 30.0 kg ha-1 mm-1 and rain water productivity indices of 1.11 and 0.95 kg m−3 for Kabode and Bungoma varieties, respectively. The baseline climate 1991-2016, current and the projected climate scenario for 2020-2039 water requirements were modelled at 579.9 and 634.1 mm, respectively thus generating a 10.2% increase in the overall sweet potato water requirement. A 0.9 yield response (Ky) was modelled to be experienced on the baseline and projected scenarios, thus 452.3 and 500.4mm supplemental irrigation water requirement for optimal yields. Variety adaptability among the test crops instituted Kabode’s acceptability within the warm-dry and warm-wet climates of the study area.