Effect of biochar on water use efficiency of legume fodder Dolichos lablab (Lablab purpureus L.) Sweet in semi-arid and arid soils of Mwea and Bura, Kenya

Production of legume fodder in arid and semi-arid regions remains a problem due to constraints of low soil moisture and limited farming technologies that can improve water retention in soil. Mwea and Bura soils are vertisols, compacted, with poor hydraulicconductivity and aeration which reduce root development. The objectives of the study were to i) improve water use efficiency of drought tolerant Dolichos lablab Rongai using biochar, ii) to determine the most suitable soil amendment rate of biochar. Percentage soil moisture content in amended plots/control was measured using a soil moisture meter at 10 cm depth. Water use efficiency was calculated based on oven-dry-weight of shoot and seed-grain at 50% flowering and maturity, evapotranspiration rate for the growing season ETo, and established crop-coefficient values (Kc) for Dolichos at respective stages of harvest postplanting. Matric potential was determined using ceramic plate pressure chamber and soil– moisture retention curves developed for 0, 3, 10 and 30 ton ha-1. Hydraulic conductivity was determined by KSAT method. Results demonstrate a significant increase of l02% in water retained between pF 0.3 and pF 10 amended at 10 t ha-1; and 70.2 % increase and 30 t ha-1 compared to the control only in Mwea soil (P< 0.05). Biochar increased porosity, hydraulic- conductivity reduced bulk density in both soils. A significantly higher water use efficiency of 4.99 kg ha-1 mm-1 at 50% flowering in Mwea soil amended at 10 t ha-1 compared to values in control and 3 t ha-1 which measured 2.2 kg ha-1 mm-1 and 3.2 kg ha-1 mm-1 p< 0.05. Based on these results, Mwea soils should be amendment with 10 t ha-1 biochar for maximizing productivity and water retention.