Soil and temperature effects on nitrification and denitrification modified N2O mitigation by 3,4-dimethylpyrazole phosphate

Abstract

Nitrification inhibitors have often been found to reduce nitrous oxide (N2O) emissions from agricultural soils, but N2O mitigation is variable and may depend on soil and climate variables. This study investigated how key abiotic factors modified the effect of Vizura®, a new formulation with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) for livestock slurry, on N2O emissions. Two different incubations were carried out to investigate the main and interactive effects of selected factors on N2O emissions after manure application to soil. Experiment 1 studied two contrasting soil textures (coarse sandy vs sandy loam soil) and temperatures (10 vs 20 °C); Experiment 2 used the coarse sandy soil to compare two levels of soil pH (4.9 vs 6.4) and nitrate availability (0 vs 50 mg N kg−1). Nitrous oxide emissions and spatial distribution of mineral N were determined in both experiments, while temporal dynamics of mineral N pools and N-cycling microbial communities were investigated in Experiment 2 only. In sandy loam soil, the efficiency of DMPP to mitigate N2O emissions after manure application was similar at 10 and 20 °C, while in the coarse sandy soil DMPP was not effective at 10 °C, possibly because of low nitrification activity. Nitrous oxide emissions from the coarse sandy soil were higher at pH 4.9 than at pH 6.4, which was accompanied by lower abundance of nosZ genes and therefore potentially higher N2O/(N2+N2O) product ratios. DMPP significantly reduced the abundance of ammonia-oxidizing bacteria (AOB) on all sampling days, but had no effect on ammonia-oxidizing archaea (AOA). The inhibitor also reduced the abundance of comammox, which are newly discovered complete ammonia oxidizers. This study showed how soil conditions (soil texture, temperature, pH), through effects on nitrifiers and denitrifiers, and mineral N distribution, can modify the efficiency of nitrification inhibitors in reducing N2O emissions from livestock slurry.