Crop and microbial responses to the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in Mediterranean wheat-cropping systems

Abstract

Nitrification inhibitors (NIs) such as 3,4,-dimethylpyrazole phosphate (DMPP), are used to suppress the abundance of ammonia-oxidising micro-organisms responsible for nitrification. In agriculture, NIs are used to retain soil mineral nitrogen (N) as ammonium to minimise the risk of losses of N from agricultural soils. It is currently unclear whether DMPP-induced nitrification inhibition can prevent losses of N from the light soils prevalent across the main rain-fed cropping regions of Western Australia, or whether it can improve the productivity or N uptake by broadacre crops such as wheat. Herein, we report on a series of glasshouse and field studies that examined the effect of applications of DMPP in conjunction with urea (as ENTEC urea; Incitec Pivot, Melbourne, Vic., Australia) on: (1) soil nitrification rates; (2) the abundance of ammonia-oxidising bacteria and archaea (AOB and AOA respectively); and (3) wheat performance (grain yield, protein content and N accumulation). A glasshouse study demonstrated that DMPP inhibited nitrification (for up to ~40 days after application) and reduced the abundance of AOB (by 50%), but had no effect on AOA abundance, wheat grain yield or protein content at any fertiliser N rate. Across six field experiments, DMPP also limited nitrification rates and reduced AOB abundance for approximately the first 40 days after application. However, by the end of the growing season, DMPP use had not increased soil mineral N resources or impaired AOB abundance compared with urea-only applications. In addition, DMPP had no effect on AOA abundance in any trial and did not improve crop performance in most trials.