Dump stability and soil fertility of a coal mine spoil in Indian dry tropical environment: a long-term study.

Plant available nitrogen, belowground (root) biomass, soil nitrogen (N) mineralization and microbial biomass N (MBN) were studied for 12 years at the interval of 2 years (0, 2, 4, 6, 8, 10 and 12 years) and mine dump stability at the intervals of 6 years (0, 6 and 12 years) after re-vegetation on coal mine spoil site. Plant available nitrogen in revegetated mine spoil ranged from 4.51 to 6.59 μg g(-1), net N-mineralization from 1.87 to 13.85 μg g(-1) month(-1), MBN from 10 to 22.63 μg g(-1), and root biomass from 28 to 566 g(-2). Mining activity has caused a change in soil characteristics including plant available nutrients like nitrate-N, ammonium-N and phosphate-P by 70, 67, and 76 %, respectively, N-mineralization by 93 %, root biomass values by 97 % and MBN values by 91 % compared to forest ecosystems. Revegetation of mine spoil produced increase in root biomass values by 1.3, 7.6 and 17.2 times, mineral N values by 1.22, 1.43 and 1.79 times, N-mineralization values by 1.8, 5.2 and 12.6 times and MBN values by 1.6, 2.0, and 3.4 times in 2, 6 and 12 years, respectively. Below ground biomass was highly co-related with microbial biomass and plant available nutrients. N-mineralization, plant available nutrients and the clay content were positively correlated with age of revegetation (P < 0.01). From the numerical modelling it was analyzed that revegetation increased the dump slope stability with a factor of safety of 1.7 and 2.1 after 6 and 12 years of plantation on dump slope, respectively, while it was 1.2 before revegetation. Thus, long term revegetation was found to have direct impact on dump stability and indirect impact on soil fertility status in mine spoil, where plant biomass and microbial biomass provide major contributions in ecological redevelopment of the mine spoil.