Temperature dependence of gross N transformation rates in two Chinese paddy soils under aerobic condition

Abstract

Temperature is an important factor that affects nitrogen (N) transformation in soils. In this study, variations in the gross and net N transformation rates between two Chinese paddy soils, namely, hydragric anthrosol (HA) and anthraquic cambisol (AC) in response to temperature (5, 15, 25, and 35 °C) were investigated by conducting an aerobic 15N dilution incubation experiment. The short-term (11 days) dynamics of gross N transformation rates was estimated using the numerical model FLUAZ. The results showed that increasing incubation temperature caused an increased gross and net transformation in the tested soils. However, the sensitivity to temperature fluctuation varied among the N transformation processes. Nitrogen mineralization was less sensitive than immobilization and nitrification at low temperatures (<15 °C). The optimum temperature for gross N nitrification in the studied paddy soils was approximately 25 °C. Higher gross N mineralization and gross N nitrification were observed in soil AC than in soil HA and were attributed to its higher pH (pH = 8.3), but further confirmation is needed. The ammonium (NH4 +) in studied paddy soils was mostly consumed through the nitrification process compared with that in the immobilization process, especially in alkaline soil AC. High consumption of NH4 + in alkaline soil AC might lead to a high risk of N loss through leaching and denitrification in case the generated nitrate (NO3 −) was not absorbed by crops in time.