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