Hedgerow pruning frequency effects on soil quality and maize productivity in alley cropping with Gliricidia sepium in Northeastern Brazil

In this study, we compared the effects of three pruning frequencies (3, 4 and 6 cuts yr−1) of Gliricidia sepium hedgerows on (i) the productivities of shoot residues and maize grain, and (ii) on chemical and physical properties of a kaolinitic soil. Productivities of gliricidia shoots (GSP) and maize grain (MGP) were evaluated from 2001 to 2003. In 2004, soil samples were taken from the experimental plots at 0–5 cm and 5–20 cm depths and analyzed for total and particulate organic C (TOC and POM-C), percent of water stable aggregates (WSA), aggregate mean weighed diameter and cation exchange capacity (CEC). An adjacent native forest and a sole maize field under conventional till were also sampled as reference areas. Increasing pruning frequency resulted in a reduction of GSP from 6 and 4 t ha−1 y−1, with 3 and 4 cuts yr−1 respectively, to 1 t ha−1 y−1, with 6 cuts yr−1. However, the 3 cuts yr−1 treatment significantly reduced MGP in about 40% and 25%, respectively in 2000 and 2001, compared to the other pruning treatments, likely due to an increased competition between the maize and gliricidia plants. The high input to the soil of gliricidia shoot biomass with 3 or 4 cuts yr−1 promoted an improvement in soil quality at the 0–5 cm soil layer characterized by an increase of 35% in POM-C and 10% in WSA, and a multivariate-based soil profile closer to that of the native forest, compared to the 6 cuts yr−1 treatment. Our results indicate that 4 cuts yr−1 of the gliricidia hedges provided the best trade-off between residue and maize grain production, and resulted in significant improvements in soil quality.