Effect of Biochar Feedstock Types on Physical and Chemical Properties of Humic Nitisols in Kakamega County, Kenya

Abstract

In Kenya, inorganic fertilisers have been extensively promoted despite concerns regarding their high cost, limited farmer knowledge, and potential environmental risks. This study evaluated the potential of biochar as a soil amendment to enhance the physical and chemical properties of humic Nitisols in Kakamega County, Kenya. A field experiment was conducted in 2022 at the Kenya Agricultural and Livestock Research Organization (KALRO) Non-Ruminant Institute, Kakamega, using a randomized Complete Block Design with three replications. Biochar (5 t ha⁻¹), derived from sugarcane bagasse, coffee husk, coffee pulp, and timber offcut, was applied alone or in combination with NPK (23:23:0) at planting and calcium ammonium nitrate (200 kg ha⁻¹) as topdressing. Maize (Hybrid 624) was grown under field conditions. Soil physical properties (bulk density, porosity, and water holding capacity) and chemical properties were analyzed using standard laboratory procedures. Sugarcane bagasse biochar combined with fertiliser reduced bulk density from 1.215 g cm⁻³ to 0.776 g cm⁻³ and enhanced soil moisture from 21.78% to 30.13%. Coffee husk biochar with fertiliser significantly increased exchangeable potassium from 0.177 cmol kg⁻¹ to 1.708 cmol kg⁻¹, while timber offcut biochar applied alone increased total nitrogen from 0.454% to 1.307%. Coffee pulp and sugarcane bagasse biochars raised total organic carbon from 0.798% to 2.98% and soil pH from 5.6 to 6.38. Overall, integrating biochar with inorganic fertiliser consistently outperformed sole applications, demonstrating a climate-smart and sustainable strategy for restoring humic Nitisols and enhancing maize production in Western Kenya.