Agroforestry adoption and its influence on soil quality under smallholder maize production systems in western Kenya

Agroforestry, a sustainable land use practice was-introduced in western Kenya in the early 1990’s as a soil fertility replenishment strategy alongside other multiple benefits. Since then, effect of the practice on soil quality is seldom evidenced. Therefore, a study was conducted in the region to assess the effects of agroforestry adoption on soil quality under small holder maize production systems. A total of 120 soil samples were collected from two land use practices: agroforestry adoption (90) and non-agroforestry adoption (30) at 0-30 cm depth from two locations (Busia and Kakamega counties). On average, adoption of agroforestry significantly improved soil physicochemical properties compared to non-adoption of agroforestry. Bulk density (BD) reduced by 21% (from 1.4 to1.1g cm ⁻³⁾ while SOC increased by 75% (0.8-1.4%), P by 80% (3.0-5.4 mg kg ⁻¹ ), exchangeable K ⁺ by 256% (0.3-8.0 Cmolc kg ⁻¹ ), Ca ²⁺ by 100% (1.0-2.0 Cmolc kg ⁻¹ ), S by 50%(0.2-0.3 mg kg ⁻¹ ), and Cu by 18% (2.8-3.3 mg kg ⁻¹ ).In reference to the soil environmental requirement for maize production, agroforestry adoption significantly increased K and Cu above the critical thresholds of 0.4 Cmolc kg ⁻¹ and 1.0 mg kg ⁻¹ , respectively regardless of the study location or adoption practice. In addition, different agroforestry tree species had variable effect on soil properties. Sesbania and leucaena significantly influenced soil BD, clay, pH, Similarly, soil available P (4.3.-7.0 mg kg ⁻¹ ), exchangeable K ⁺ (0.4-0.7 cmolc kg ⁻¹ ), Mg (0.1-0.2 cmolc kg ⁻¹⁾ , and Mn (13.5 – 25.2 mg kg ⁻¹ ) above non-agroforestry adoption at both locations, while calliandra significantly increased SOC in Kakamega only.