Does a soil drying-rewetting cycle decrease the effectiveness of nitrification inhibitors?

Abstract

Changes in soil moisture content can be an important factor influencing the effectiveness of nitrification inhibitors (NIs). Therefore, we hypothesized that a soil drying-rewetting cycle enhances biodegradation and decreases the effectiveness of NIs. This study evaluated the effectiveness of DMPP and MP+TZ (3-Methylpyrazol and Triazol) under a drying and rewetting cycle relative to low and high soil moisture conditions under two soil textures. NIs performance was assessed through measuring (i) daily and cumulative N2O-N emissions, (ii) soil NH4+-N and NO3−-N concentrations, and (iii) the composition of bacterial soil communities over the experimental period in an incubation study. NIs application reduced the overall N2O-N emissions under drying-rewetting (-45%), 40% water-holding capacity (WHC) (-39%), and 80% WHC (-25%). In general, the relative abundance of nitrifying bacteria Nitrospira spp., Nitrosomonas, Nitrobacter, and Nitrosococcus was reduced by DMPP and MP+TZ application, explaining the observed results. Unexpectedly, between days 30 and 60, DMPP and MP+TZ inhibitory effect on nitrification was weakened, and the N2O-N emissions from NI-treated soils increased by 5 to 6-fold relative to the control treatment in the silt loam soil at 80% WHC. These results indicated that DMPP and MP+TZ application can cause late increased N2O-N release due to short-term effects on the relative abundance of nitrifying bacteria and subsequent NO3−-N accumulation. Thus, our study provided new insights into how the interaction between time and soil water content can decrease the effectiveness of NIs.