Restoring productivity of degraded mined soils using legume leaf residues as organic amendments

Scarcity and cost of topsoil and conventional materials make legume residues a promising alternative for reclaiming land degraded by opencast mining. This study examined plant residues by evaluating the effect of their quality (C:N ratio, lignin, polyphenols) on soil organic carbon (SOC), total soil nitrogen (TN) and crop (maize, cowpea) performance. A 12-month pot experimentation in Kumasi (Ghana) tested leafy residues of Leucaena leucocephala, Gliricidia sepium, Mucuna pruriens, Pueraria phaseoloides, and Panicum maximum (control), applied at four rates (0, 10, 20, 30 t ha⁻¹ dry weight) using a factorial randomized complete block design with four replications. Legumes had higher N content (≈ 3.5% by Leucaena) and higher quality indices (highest PRQI of 4.7 by Gliricidia), but lower lignin content than Panicum. SOC and TN gains were high (≈ 500% SOC and > 800% TN gains by Mucuna and Leucaena, respectively), explained by low initial concentrations of the substrate. Although mineralization was slow, plant quality indicators correlated with SOC and TN. Maize, other than cowpea, responded well to residues, with Leucaena (30 t ha⁻¹) yielding the highest dry matter (≈ 4.2 t ha⁻¹). Legume residues provide a sustainable solution for reclaiming opencast-mined land, showing subsoil improvement potential that requires field trials to validate pot-scale findings.