Cultivation impacts nitrogen transformation in Indian forest ecosystems

Abstract

Two forests and two croplands, converted from the forest ecosystem were studied for 2 years to quantify inorganic N, nitrification, N-mineralization and microbial-N. The available N-pool ranged from 15.23 μg g⁻¹ to 19.84 μg g⁻¹, microbial-N from 20.6 μg g⁻¹ to 80.02 μg g⁻¹ with maximum values in summer season and minimum values in the rainy season. The trend for nitrification and N-mineralization was opposite to that of the size of available N-pool. Mean annual net nitrification rates ranged from 7.07 μg g⁻¹ month⁻¹ to 44.84 μg g⁻¹ month⁻¹ (0.17–1.39 μg g⁻¹ day⁻¹) and net N-mineralization from 6.56 μg g⁻¹ month⁻¹ to 48.53 μg g⁻¹ month⁻¹ (0.21–1.56 μg g⁻¹ day⁻¹). On an average, the pool of available N was slightly higher by 4.81%, while the microbial-N was declined substantially by 41.78% after the conversion of forest into cropland. Cultivation reduced the mean annual net nitrification and net N-mineralization, respectively by 50.71% and 47.67%. Interestingly, seasonal moisture content is negatively correlated to microbial-N and inorganic N and positively related to nitrification and N-mineralization.