Thermal transformation of nitrogen in a subtropical mixed oak forest of Manipur, Northeast India

The thermal transformations of nitrogen and other soil parameters were studied during October 2007-September 2008 in a control (CL) and burnt (BT) forest sites of a subtropical forest of Manipur, Northeast India dominated by Quercus serrata and Schima wallichii by using the buried bag technique. In the present study burning treatment significantly increases total nitrogen and soil moisture. Two-way ANOVA testing the effect of burning and months revealed that the rates of nitrification and nitrogen mineralization exhibited an insignificant transient increase while ammonification exhibited a significant difference due to the variance in months. The NO3-N concentration ranged from 0.31 to 10.9 mg kg− 1 and NH4-N concentrations varied from 1.84 to 29.5 mg kg− 1 across the sites. In CL significant influential factors of nitrification are total nitrogen (TKN) and air and soil temperature while for ammonification and N mineralization total organic carbon (TOC) but total nitrogen and soil temperature also exhibited significance with ammonification. In BT, none of the abiotic variables have significant influence but rainfall exhibited significant difference with ammonification while air and soil temperature with nitrogen mineralization. Present study concludes that the process of nitrogen transformation in soil is site specific and regulated by the climatic and edaphic factors and upon burning there is a transient increase in soil nutrients especially nitrates (14.07%) and nitrogen mineralization (44.69%) but nitrification and ammonification decrease by 16.26% and 30.92% respectively. Hence, mild fire with proper management and monitoring can be used as a tool to improve the nutrient and fertility in nitrogen limited ecosystems.