Effects of soil properties on urea-N transformation and efficacy of nitrification inhibitor 3, 4-dimethypyrazole phosphate (DMPP)

Ammonia (NH3) and nitrate (NO3−) are two major sources of N loss during the urea-N transformation process in soil. 3, 4-dimethypyrazole phosphate (DMPP) is a nitrification inhibitor that could effectively limit the NO3 – production process but aggravate NH3 emissions. NH3 volatilization, NO3 – production and the efficiency of DMPP are all influenced by different soil factors. The objective of this study was to understand the effects of soil properties on N losses after urea application and DMPP efficacy. A laboratory incubation experiment was set up with urea applied to seven different types of soil at a rate of 0.25 g N/kg soil, with or without DMPP, (at a rate of 1% of the N applied in the fertilizer). Urea content, NH3 losses and mineral N were measured regularly for 50 days after treatment addition. NO3–N production rates, inhibition efficiencies of DMPP and urea half-lives were calculated based on the measured NO3–N and urea concentrations. Results showed that urea half-life was negatively correlated with soil total organic carbon (TOC) (r = −0.930). NO3 – production rate was correlated with soil pH (r = 0.670), sand (r = 0.639) and clay content (r = −0.632). The efficiency of DMPP for inhibiting NO3 – production was positively correlated with NO3 – production rate (r = 0.721). NH3 volatilization was positively correlated with soil pH (r = 0.657) and sand content (r = 0.687) and negatively correlated with urea half-life (r = −0.586). Greater inhibition efficiency of DMPP led to higher NH3 losses. Urea degradation, NH3 loss, NO3 – production rate and the inhibition efficiency of DMPP were significantly affected by soil properties and the risk of NH3 volatilization was increased by DMPP application.