Nitrification inhibitor DMPP mitigated N2O emissions and decreased N2 losses in a low-nitrate vegetable soil after application of manure

In China, amounts of organic manure as basal fertilizer application along with flooding irrigation usually resulted in large N₂O emissions from intensively protected vegetable soils. However, little attention paid on the N₂O emission bursts after application of manure, in a newly established vegetable soil with a low-nitrate content. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), can be used to reduce N₂O emissions from agricultural soils, little is known about how DMPP affect N₂ emissions and gaseous nitrogen (N₂O+N₂) losses. Here, we conducted a microcosm experiment in a robotized incubation system under an aerobic (O₂/He) condition. Dried chicken manure was applied with and without DMPP to a protected vegetable soil. Two drying-rewetting events occurred during the 19 days monitoring period, and the relevant soil properties (e.g., NO₂^-, WFPS, DOC, DON, SMBC) were analyzed. Our results showed DMPP addition strongly retarded soil nitrification process that kept a higher NH₄⁺ concentration than that of only manure application. A significant decline of NO₂^- and NO₃^- concentration was found in a manure-treated soil with DMPP addition. Clearly, DMPP addition significantly reduced N₂O emissions from the protected vegetable soil by 77.0% and remarkably decreased N₂ emissions and overall N₂O+N₂ losses (compared with manure alone) by 51.9% and 54.0%, respectively. Pearson analysis showed that soil N₂O fluxes were significantly related to soil WFPS, NH₄⁺, SMBC (P<0.01) and SMBN (P<0.05), whereas N₂ fluxes were significantly correlated with soil WFPS, SMBC (P<0.01), NO₂^-, NH₄⁺ and SMBN (P<0.05) during the whole incubation. The fluxes of N₂O+N₂ were positively correlated with WFPS, NO₂^-, SMBC and SMBN, whereas negatively correlated with NH₄⁺ (P<0.05). Moreover, the ratio of N₂O to N₂O+N₂ (N₂O/(N₂O+N₂)) was positively correlated with NO₃^- (P<0.05), and negatively correlated with DOC, DON and SMBC (P<0.01). An aggregated boosted tree (ABT) analysis further indicated that the relative influence of WFPS, SMBC and NH₄⁺ on N₂O fluxes were 19.4%, 14.9% and 12.8%, respectively. Moreover, the relative influence of WFPS on N₂ fluxes was the largest (47.4%), followed by SMBC and SMBN (14.3% and 9.66%, respectively). In addition, the relative influence of WFPS, SMBN and SMBC on N₂O+N₂ losses were 32.6%, 17.0% and 12.6%, respectively, and the relative influence of SMBC, DOC and NO₂^- on N₂O/(N₂O+N₂) were 22.5%, 20.2% and 11.1%, respectively. In conclusion, our data show that DMPP combined with manure can significantly reduce N₂O and N₂ emissions in a low-nitrate newly established vegetable soil, and their emissions were strongly affected by WFPS.