Ecological restoration of mined-out areas of dry tropical environment, India

The objective of the present study was to evince the long-term changes after natural revegetation and experimental revegetation of the coal mine spoils with respect to total plant biomass, available plant nutrients, nitrogen transformation and microbial biomass N (MBN) in dry tropical environment of India. Total plant biomass (above- and below-ground), plant available nitrogen, soil nitrogen mineralization and microbial biomass N (MBN) were studied for 2 years in 5 and 10 years old naturally vegetated and revegetated coal mine spoils, and dry tropical forest ecosystem of India. In forest ecosystem, the above ground biomass values ranged from 3,520 to 3,630 kg ha−1 and belowground from 6,280 to 6,560 kg ha−1. Plant available nitrogen ranged from 16.76 to 23.21 μg g−1, net N-mineralization from 9.8 to 48.53 μg g−1 month−1 and MBN from 26.4 to 80.02 μg g−1. In naturally revegetated mine spoil, the above ground biomass values ranged from 1,036 to 1,380 kg ha−1 and belowground from 2,538 to 3,380 kg ha−1. Plant available nitrogen ranged from 7.33–17.14 μg g−1, net N-mineralization from 3.1 to 12.46 μg g−1 month−1 and MBN from 14.2 to 35.44 μg g−1. In revegetated mine spoil, the above ground biomass values ranged from 1,224 to 1,678 kg ha−1 and belowground from 2,870 to 4,130 kg ha−1. Plant available nitrogen ranged from 9.4 to 18.83 μg g−1, net N-mineralization from 4.2 to 16.2 μg g−1 month−1 and MBN from 21.6 to 42.6 μg g−1. The mean plant biomass values in 5 and 10 years mine spoils was lower compared to forest ecosystem by 2.5 and 2 times, respectively. N-mineralization value in 5 year mine spoil was 3.5 times lower and in 10 years mine spoil 2 times lower compared to forest ecosystem. The MBN value was about 2 times lower in both 5 and 10 year mine spoils compared to native forest. MBN was positively related to the re-vegetation age of the mine spoil.