Evaluation of nitrogen mineralization under various irrigation water qualities and nitrogen application rates for mulched drip irrigation in an arid region

Understanding the interactive effects of irrigation water quality and fertilization on nitrogen mineralization (N-min) and accurately predicting N-min are of great importance for the secure and efficient utilization of brackish water in arid regions. A pot experiment was conducted to determine the N-min under different drip irrigation water salinities and nitrogen application rates and to modify the nitrogen mineralization potential (N-0) and mineralization rate constants (k) of the first-order kinetic equation of N-min. An in situ field experiment was conducted to validate the modified equation. The results showed that the amounts of N-min for water salinities of 1.27, 3.03, and 4.90 g L-1 were 58.9, 76.1, and 45.4 kg ha(-1), respectively. N-min was stimulated when the soil salinities were lower than 6.6, 6.1 and 3.9 g kg(-1) for nitrogen application rates of 255, 315 and 375 kg ha(-1), respectively. Nitrogen application significantly reduced N-min. When the nitrogen application rate increased to 375 kg ha(-1), the net N-min rate remained lower, and the effects of salinity on N-min were attenuated. The N-min model with modified N-0 and k values was developed considering the impacts of soil organic nitrogen, nitrogen application rate, and soil salinity. Model testing indicated that the modified model provided an acceptable estimation of N-min under field conditions. It will be helpful for developing rational fertilization strategies of drip irrigation with brackish water in arid regions.