Effect of forage grass (Pennisetum pedicellatum) and legume (Stylosanthes hamata) revegetation on recovery of soil fertility in a reclaimed hazardous waste dump

Abstract

Dumping of hazardous waste causes land degradation, air, and water pollution, deteriorates landscape and aesthetics, which can be controlled by reclaiming with grass-legume seeding. The study aimed to examine the effect of grass-legume revegetation between 1-and 5-years in a restored waste dump (hazardous waste of an integrated steel plant) reclaimed with coir-matting, topsoil blanketing followed by grass (Pennisetum pedicellatum) and legume (Stylosanthes hamata) seeding. We hypothesized that the synergistic effect of the grass-legume mixture would lead to an increase in productivity and soil fertility. To assess the effects, changes in root and shoot biomass, mulch accumulation, nitrogen (N) mineralization, and its effect on soil fertility were measured. Our results showed between 1-to 5-years legume and grass biomass increased by 44% and 37%, respectively. An increase in mulch density and thickness along with revegetation age potentially increased the soil moisture by 7.5% and lowered soil temperature by 9°C at 10 cm depth. Cumulative N-mineralization by legume was three-fold higher than the grass. Soil organic carbon (SOC), available N, total N, N-stock, and soil respiration was doubled after 5-years of revegetation. Dehydrogenase and urease activity increased by 44% and 56% respectively, indicating greater C and N accumulation at the dump surface. The study concluded that grass (P. pedicellatum) and legume (S. hamata) mixture can be used for reclamation of the waste dump that accelerates recovery of the fertility of disturbed topsoil by contributing mulch with increasing age of revegetation.