The long-term effects of a gliricidia–maize intercropping system in Southern Malawi, on gliricidia and maize yields, and soil properties

A gliricidia–maize (Gliricidia sepium (Jacq.)–Zea mays L.) simultaneous intercropping agroforestry system has shown to be a suitable option for soil fertility improvement and yield increase in highly populated areas of sub Saharan Africa where landholding sizes are very small and inorganic fertilizer use is very low. An 11 year old field experiment, gliricidia–maize simultaneous intercropping, with and without a small application of inorganic fertilizer was studied to increase our understanding of the long-term effects of continuous applications of gliricidia prunings on maize yield and soil chemical properties. The main objectives were to assess: (1) the yield of gliricidia prunings under intensive pruning management, (2) the effect of continuous applications of gliricidia prunings and fertilizer on maize yield and soil properties. During 11 years of intensive pruning, gliricidia trees maintained high levels of leafy biomass production (4–5 Mg DM ha−1). Application of gliricidia prunings increased maize yield three-fold over sole maize cropping without any soil amendments (3.8 and 1.1 Mg ha−1, respectively). Maize yield declined with time under sole maize cropping system in both treatments with and without inorganic N fertilizer. Application of inorganic fertilizer (46 kg N ha−1) in agroforestry systems increased maize yield by 29% (P = 0.002). Application of inorganic P did not significantly increase maize yield implying that the native P in the topsoil and P recycled through gliricidia prunings application was enough to support maize growth. The trees took up “native” soil nutrients (P, Ca, Mg and K) from the depth and pumped these to the surface soil. A net soil nutrient decrease in the gliricidia–maize simultaneous intercropping system was observed due to increased nutrient export.