Nitrification inhibitor DMPP mitigated N2O emissions and decreased N2 losses in a low-nitrate vegetable soil after application of manure&#160;
Authors: Liu Yanting , Yin Junhui , Cao Wenchao 
Published: March 2021

&lt;p&gt;In China, amounts of organic manure as basal fertilizer application along with flooding irrigation usually resulted in large N&lt;sub&gt;2&lt;/sub&gt;O emissions from intensively protected vegetable soils. However, little attention paid on the N&lt;sub&gt;2&lt;/sub&gt;O 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 N&lt;sub&gt;2&lt;/sub&gt;O emissions from agricultural soils, little is known about how DMPP affect N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;emissions and gaseous nitrogen (N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;) losses. Here, we conducted a microcosm experiment in a robotized incubation system under an aerobic (O&lt;sub&gt;2&lt;/sub&gt;/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., NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, WFPS, DOC, DON, SMBC) were analyzed. Our results showed DMPP addition strongly retarded soil nitrification process that kept a higher NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&amp;#160;concentration&amp;#160;than that of only manure application. A significant decline of NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;&amp;#160;and NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;&amp;#160;concentration was found in a manure-treated soil with DMPP addition. Clearly, DMPP addition significantly reduced N&lt;sub&gt;2&lt;/sub&gt;O emissions from the protected vegetable soil by 77.0% and remarkably decreased N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;emissions and overall N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;losses (compared with manure alone) by 51.9% and 54.0%, respectively. Pearson&amp;#160;analysis showed that soil N&lt;sub&gt;2&lt;/sub&gt;O fluxes were significantly related to soil WFPS, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;, SMBC (P&lt;0.01) and SMBN&amp;#160;(P&lt;0.05), whereas N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;fluxes were significantly correlated with soil WFPS, SMBC (P&lt;0.01), NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&amp;#160;and&amp;#160;SMBN (P&lt;0.05)&amp;#160;during the whole incubation.&amp;#160;The fluxes of N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;were positively correlated with WFPS, NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, SMBC and SMBN, whereas&amp;#160;negatively correlated with NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&amp;#160;(P&lt;0.05). Moreover, the ratio of N&lt;sub&gt;2&lt;/sub&gt;O to N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;(N&lt;sub&gt;2&lt;/sub&gt;O/(N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;))&amp;#160;was positively correlated with NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;&lt;sup&gt;&amp;#160;&lt;/sup&gt;(P&lt;0.05), and negatively correlated with DOC, DON and SMBC (P&lt;0.01). An aggregated boosted tree (ABT) analysis further indicated that the relative influence of WFPS, SMBC and NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;&amp;#160;on N&lt;sub&gt;2&lt;/sub&gt;O&amp;#160;fluxes&amp;#160;were 19.4%, 14.9%&amp;#160;and 12.8%, respectively. Moreover, the relative influence of WFPS on N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;fluxes&amp;#160;was the largest (47.4%), followed by SMBC and SMBN (14.3% and 9.66%, respectively).&amp;#160;In addition, the relative influence of WFPS, SMBN and SMBC on N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;losses were 32.6%, 17.0% and 12.6%, respectively, and the relative influence of SMBC, DOC and NO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;&amp;#160;on N&lt;sub&gt;2&lt;/sub&gt;O/(N&lt;sub&gt;2&lt;/sub&gt;O+N&lt;sub&gt;2&lt;/sub&gt;) were 22.5%, 20.2% and 11.1%, respectively. In conclusion, our data show that DMPP combined with manure&amp;#160;can significantly reduce N&lt;sub&gt;2&lt;/sub&gt;O and N&lt;sub&gt;2&lt;/sub&gt;&amp;#160;emissions&amp;#160;in a low-nitrate newly established vegetable soil, and their emissions were&amp;#160;strongly affected by WFPS.&amp;#160;&lt;/p&gt;