Influence of different land uses on soil nitrogen transformations after conversion from an Indian dry tropical forest

The effects of alternate land uses, such as grassland, cropland and mine spoil on mineral nitrogen (N), N-transformation rate and microbial biomass N (MBN) in dry tropical forest soils of India were studied. The mean annual mineral N in the forest, grassland, cropland and mine spoil ecosystems, respectively ranged from 15.24 to 19.58, 17.8 to 18.56, 16.49 to 19.85 and 10.52 to 13.44 mu g g(-1), net nitrification rate from 14.15 to 23.4, 10.11 to 11.38, 8.07 to 9.16,10.52 to 13.44 mu g g(-1) mo(-1); net N-mineralization rate from 17.38 to 26.36. 13.99 to 15.41, 10.99 to 12.5, 5.43 to 7.68 mu g g(-1) mo(-1) and and microbial biomass N from 41.25 to 58.87, 34.47 to 47.95, 27.88 to 30.43 and 22.95 to 25.26 mu g g(-1), respectively. The values were within the range reported by previous studies in different tropical environments. The mean annual net nitrification rates declined after conversion into grassland, cropland and mine spoil by 43, 54 and 78%, respectively, net N mineralization by 33, 46 and 70%, and microbial biomass N by 29%, 42% and 52%, respectively. The MBN was positively related to root biomass and total plant biomass, while microbial-N and inorganic N are reciprocally. while nitrification and N-mineralization are directly related to seasonal soil moisture and temperature. The microbial biomass N, nitrification and N-mineralization are negatively related to smaller fraction (<0.1 mm) of the soil. Above- and below-ground biomass also have had their impact on microbial biomass N, and thereby N-mineralization. Thus, in dry tropical forests, land-use change affects remarkably the nitrogen transformation process in soil. (C) 2009 Elsevier B.V. All rights reserved.