Spatial and temporal trends in soil N-mineralization rates under the agroforestry systems in Bhabhar belt of Kumaun Himalaya, India

To access the process of nitrogen mineralization in soil, the buried-bag technique was used among traditional agroforestry systems in the Bhabhar belt of Kumaun Himalaya. The present study, determined the relationship between various parameters of N-mineralization with agroforestry systems, seasons and soil depths. Season and soil depth have significantly (p < 0.001) affected the process of ammonification, nitrification and net N-mineralization. The soil ammonium-N pool was comparatively higher than the nitrate-N pool. Highest amount of ammonium and nitrate-N were recorded in the agri-horticulture (AH) system, and lowest in the agri-horti-silviculture (AHS) system. Among the systems, highest amount of inorganic-N (ammonium + nitrate) was recorded during rainy season while, lowest during winter season. The highest ammonification rate (6.47 +/- 1.47 mg kg(-1) month(-1)) was observed in agri-silviculture system and lowest (5.67 +/- 1.68 mg kg(-1) month(-1)) in AHS system, while nitrification value was maximum (2.53 +/- 0.40 mg kg(-1) month(-1)) in AH system and minimum (2.23 +/- 0.37 mg kg(-1) month(-1)) in AHS system. The values of net N-mineralization were ranged from 4.03 +/- 0.53 to 13.29 +/- 0.44 mg kg(-1) month(-1). The values of inorganic-N and net N-mineralization were significantly more (P < 0.01) in the surface soil layer (0-20 cm) than the subsurface layers (20-40 cm and 40-60 cm). Nitrogen mineralization was negatively correlated with the soil pH and positively correlated with soil organic carbon and total soil nitrogen. Higher rate of N-mineralization in AHS system indicated rapid turnover of nitrogen due to soil management practices and suggested that the changes in agroforestry based land-use systems alter the process of net N-mineralization, nitrification and ammonification.

Automated summary

The study explored nitrogen mineralization in traditional agroforestry systems using the buried-bag technique in the Bhabhar belt of Kumaun Himalaya. Results showed that season and soil depth significantly affected ammonification, nitrification, and net N-mineralization processes, with differences observed in nitrogen pools and rates among different agroforestry systems.