Integrated Use of Biochar, Hydrogels, and Manure Improves Green Gram (Vigna radiata) Productivity in Kwale County, Kenya

Abstract

Land degradation, low soil fertility, limited moisture retention and climate variability continue to constrain green gram (Vigna radiata L.) production in smallholder farming systems in coastal Kenya. This study evaluated the effects of biochar, farmyard manure and Hydrogel on soil fertility, soil moisture, crop growth and grain yield of green gram under farmer-managed conditions in Kwale County, Kenya. Field experiments were conducted in Matuga, Lunga Lunga, Msambweni and Shimba Hills using a randomised complete block design with three replications. Treatments consisted of biochar at 10 t ha⁻¹, farmyard manure at 10 t ha⁻¹, Hydrogel at 5 kg ha⁻¹ and an untreated control. Data were collected on soil moisture, soil organic carbon, total nitrogen, pH, exchangeable phosphorus, potassium and sulphur, plant height and grain yield. Analysis of variance was performed in R, and treatment means were separated at the 5% significance level. Biochar and farmyard manure generally produced the greatest improvements in soil fertility and crop performance. Biochar increased soil moisture, soil organic carbon, total nitrogen, pH and exchangeable phosphorus by 35%, 34%, 49%, 12% and 153%, respectively, compared with the control. Farmyard manure increased the same parameters by 33%, 28%, 36%, 11% and 133%, respectively. Hydrogel produced moderate improvements, particularly in soil moisture. Grain yield increased by 43% under biochar, 36% under farmyard manure and 20% under Hydrogel relative to the control.