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

Abstract

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.