Alley cropping sequentially cropped maize and cowpea with Leucaena on a sandy soil in Southern Nigeria

The potential of alley cropping maize and cowpea with the giant Leucaena (Leucaena leucocephala (Lam) de Wit) cultivar K-28 was studied on an Entisol (Psammentic Ustorthent) in Southern Nigeria. In this trial the crops were grown in 4 m wide alleys formed by periodically pruned leucaena hedgerows. The effect of application of leucaena prunings, nitrogen fertilizer and tillage was studied. Despite the very intensive pruning regime (five prunings/year) for a six-year period, the leucaena hedgerows continue to produce substantial amounts of prunings, nitrogen yield and stakes. Application of nitrogen to the maize crop increased dry matter and nitrogen yield from the leucaena prunings. Although high nitrogen yield was obtained from the prunings, the application of low nitrogen rates was still needed for obtaining a high maize yield. Maize grain yield can be sustained at about 2.0 t/ha with continuous application of leucaena prunings only. Without application of leucaena prunings and nitrogen maize yield continued to decline with subsequent croppings. Cowpea grain yield was not affected either by leucaena prunings or by residual nitrogen. Tillage (rototilling) resulted in either higher or the same maize and cowpea yields as compared with no-tillage. Application of leucaena prunings resulted in higher soil moisture retention, organic matter, exchangeable K, Ca, Mg, and also nitrate levels in the soil solution. Leucaena and maize appear to extract soil moisture from different zones in the soil. Timely pruning of hedgerows is necessary to minimize shading.