Rice straw biochar and irrigation effect on yield and water productivity of okra

Dry season vegetable production is challenging due to water scarcity, a drawback on sustaining year-round crop production. Biochar improves soil moisture and nutrient retention and may be used to improve vegetable water productivity. We examined the combined effect of rice straw biochar and irrigation on yield, water productivity, and phosphorus (P) uptake of okra (Abelmoschus esculentus L.) grown on a sandy clay loam soil in the dry season. Biochar was applied at 0, 5, 10 Mg ha⁻¹, and 10 Mg ha⁻¹ biochar fortified with P [10 Mg ha⁻¹_(P)] under full irrigation (FI) and deficit irrigation (DI) and replicated in each growing season for three years. Under DI, the 10 Mg ha⁻¹ and 10 Mg ha⁻¹_(P) biochar treatments significantly (p <.05) increased okra fresh fruit yield (Y_FF) by 67 and 82% but had no impact on total aboveground biomass yield (Y_TBM) in the first growing season. Biochar at 5 Mg ha⁻¹ had no impact on okra yield. Okra yield was higher under biochar fortified with P compared to the traditional method of applying P alone, e.g. 30 Mg ha⁻¹_(P) produced significantly higher Y_TBM than 30 Mg ha⁻¹ under DI. Biochar had no impact on P uptake in the first growing season. Estimated okra water use was 224 and 193 mm under FI and DI. Yield reduction under DI compared to FI was only 8%. Amid water scarcity, a minimum of 10 Mg ha⁻¹ rice straw biochar under DI is therefore recommended for farmers in the area.