Nutrient recycling and physical indicators of an alley cropping system in a sandy loam soil in the pre-Amazon region of Brazil

The sustainable management of soils has proved a key challenge for the smallholder agriculture in southeastern Amazonia, Brazil. We assessed the capacity of an alley cropping system to sustain corn productivity. The experiment included six treatments: Clitoria + Pigeon Pea; Leucaena + Pigeon Pea; Acacia + Pigeon Pea; Clitoria + Leucaena; Leucaena + Acacia and Control treatment (no legumes). We determined chemical and physical indicators of soil quality. Leucaena had the highest macronutrient concentrations (40.17 g N kg−1), except for P. All legumes had high Ca (13.82–17.84 g kg−1) and very low P (0.51–2.83 g kg−1) and Mg (1.73–2.92 g kg−1) concentrations. Acacia had the lowest N, P, K and Mg concentrations. Pre-planting soil analysis indicated that soil quality indicators were below the critical levels needed for a productive agricultural system, especially for phosphorus, sum of bases and base saturation. Physical indicators of quality, such as bulk density (1.40–1.30 Mg m−3), total porosity (0.46–0.50 m m−3) and soil aeration capacity (0.10–0.17 m m−3), were substantially improved as a result of the surface application of residues. There was a cumulative effect of residue application on corn crop productivity. Because of its capacity to recycle nutrients and improve soil quality over the period of 3 years, alley cropping in association with no-tillage, can be an efficient strategy for maintaining productivity in the low-fertility soils of the humid tropics.