Winter soil temperature and its effect on soil nitrate Status: A Support Vector Regression-based approach on the projected impacts

Winter season is characterized by lowering of air temperature and soil temperature, and deceleration of soil nitrogen cycle. Despite low soil temperature, soil NO3- is found on the soil surface and in the streams of temperate and higher latitude regions towards the end of winter season. With the rise in global air temperature, the soil temperature is expected to warm up accordingly. Plausible effects of future soil temperature changes in affecting the production and movement of soil NO3- within a vertical profile were studied in the present paper. Four Representative Concentration Pathways (RCP) scenarios were considered to estimate the effects of change in air temperature on soil temperature at different depths within a vertical profile and on the soil nitrate status. Since winter season is known to have low to no soil nitrate utilization (due to microbial inactivity and low utilization by biomass), plausible effects of winter warming in the future decades were studied. The occurrence and movement of soil NO3- during winter, raises a concern regarding the future warming climate's response. Long-term records from Hubbard Brook Experimental Forest, New Hampshire, USA, were used for observation, calibration, and validation purposes. Non-linear relationship between air temperature, soil moisture, soil temperature, and soil NO3- status at different soil depths, were assessed using support vector regression (SVR) models. Soil temperature and soil NO3- status at different soil depths were predicted using SVR models, under the four different RCP scenarios. The projections under different RCP scenarios suggested - significant production of soil NO3- during winter (approx. 18 mg/l by the year 2095 under a business as usual scenario), and movement of soil NO3- towards soil surface before the beginning of plant-growing season.

Automated summary

This study investigates the potential effects of future soil temperature changes on the production and movement of soil NO3-. The projections under different scenarios suggest significant production of soil NO3- during winter and movement towards the soil surface before the beginning of the plant-growing season.