Enhancement of the rootability of a structurally fragile tropical soil using gypsum and leguminous residues to increase the yield of maize

In humid tropical areas, a combination of factors related to soil conditions for root development contribute to decreased nutrient use efficiency. Our aim was to evaluate the combined effects of the application of gypsum and mulch from leguminous trees on rootability of root zone soil, root growth, phosphorus recovery efficiency and maize yield in a sandy loam soil prone to hardsetting. The experiment involved a randomized block design with four replications and six treatments: no residue or gypsum (control, C); leguminous residues (L); leguminous residues and 6 t/ha of gypsum (LG6); urea and 6 t/ha of gypsum (UG6); leguminous residues, urea and 6 t/ha of gypsum (LUG6); and leguminous residues, urea and 12 t/ha of gypsum (LUG12). Application of gypsum plus leguminous residues enhanced soil rootability, when applied to a tropical Arenic Hapludult, through the combined effects of increased porosity and decreased penetration resistance. These improvements facilitated root growth in deeper soil layers and greater nutrient uptake. Application of leguminous residues increased the input and retention of calcium in deeper layers. The use of large amounts of gypsum with leguminous residue, despite a significant increase in phosphorus uptake, did not result in a proportional increase in maize yield. Given the small differences in calcium content between the 6 and 12 t/ha gypsum treatments, applying a low dose of gypsum combined with leguminous residue, rather than administering a single large gypsum dose, is recommended for tropical sandy loam soils with low cation retention capacities.