Combined Inhibition Effect Of Biogas Slurry Application And NBPT-DCD On Soil N₂O Emission

High emission of nitrous oxide(N₂O)from farmland soil is caused by a large amount of available nitrogen in the biogas slurry and the traditional flooding fertilization.At present,there are many technical means to reduce N₂O emission,among which nitrogen fertilizer synergist is an effective choice.Urease inhibitor and nitrification inhibitor can control nitrous oxide emission caused by unreasonable fertilization from the source by acting on different ways of producing N₂O in soil.In this study,the effects of nitrification/urease inhibitor(N-(n-Butyl)Thiophosphoric Triamide+Dicyandiamide),fertilizer application methods and soil water content on N₂O emission,and the effects of nitrification/urease inhibitor(N-(n-Butyl)Thiophosphoric Triamide+Dicyandiamide)on nitrification and denitrification functional genes and microbial action mechanism at different fertilizer application depths were explored.The results are as follows:(1)The application of biogas slurry has a significant effect on soil N₂O emission(p<0.01).Under the condition of no inhibitor,compared with surface application,the application of biogas slurry covered with soil significantly reduced soil N₂O emission(p<0.01),and the cumulative emission of soil N₂O decreased by 21.9%-72.9%.Adding inhibitors significantly affected soil N₂O emission(p<0.05).Compared with surface application,biogas slurry combined with 1%N-(n-Butyl)Thiophosphoric Triamide and 5%Dicyandiamide had the best overall inhibition effect on soil N₂O,CO₂ and NH₃,and the cumulative emission of soil N₂O decreased by 6.0%-33.8%compared with the treatment without inhibitors.(2)Adding 1%N-(n-Butyl)Thiophosphoric Triamide and 5%Dicyandiamide can reduce N₂O emission in soil under certain water content.Under the condition of no inhibitor,with the increase of soil water content,the soil N₂O emission showed an increasing trend.The cumulative emission of N₂O from soil treated with 80%WHC was 35.5 and 18.0 times higher than that of 40%WHC and 60%WHC respectively,with significant difference(p<0.05).Under the condition of adding inhibitor,the cumulative emission of N₂O in soil of 40%WHC and 60%WHC decreased by 35.5%and 41.8%respectively.Under the condition of high water content(80%WHC),adding 1%N-(n-Butyl)Thiophosphoric Triamide and 5%Dicyandiamide has little inhibitory effect on soil N₂O emission.(3)The depth of soil covered by biogas slurry,inhibitors and their interactions all have significant effects on N₂O emission from soil(p<0.01).Under the condition of no inhibitor,with the increase of the depth of soil covered with fertilizer solution(0-15 cm),the cumulative emission of soil N₂O increased.The cumulative emission of soil covered with biogas slurry for 15 cm was 4.7,1.2 and 0.7 times higher than that of soil covered with biogas slurry for 10 cm,5 cm and surface application treatment,respectively,with significant differences(p<0.05).Under the condition of adding inhibitor,the N₂O emission of soil covered with biogas slurry for 15 cm and 10 cm and surface application treatment significantly inhibited,and the cumulative emission of N₂O decreased by 46.1%,21.7%and 34.6%respectively compared with the treatment without inhibitor.(4)The depth of fertilizer application and inhibitors have significant effects on the number of functional genes of microorganisms.Under the condition of no inhibitor,the copy numbers of 16Sr RNA,AOA-amo A,AOB-amo A,nirS,nirK and nos Z in the soil covered with biogas slurry for 15 cm and surface application were significantly higher than those in the soil covered with 10 cm and 5 cm.Under the condition of adding inhibitor,the copy number of each functional gene increased with 15 cm soil covering and surface treatment.After 5 days of application,the copy numbers of 16Sr RNA,AOA-amo A,AOB-amo A,nirS,nirK and nos Z increased by 208.3%,582.6%,389.0%,93.2%,280.6%and 263.6%,respectively,compared with the treatment without inhibitor.Compared with the treatment without inhibitor,the copy numbers of 16Sr RNA,AOA-amo A,AOB-amo A,nirS,nirK and nos Z increased by 450.0%,77398.8%,226.5%,384.6%,194.4%and 273.8%respectively.(5)Redundancy analysis(RDA)showed that the addition of inhibitors changed the microbial pathway of soil N₂O production.Under the condition of no inhibitor,soil N₂O was mainly produced by ammonia oxidation dominated by AOB-amo A gene,and the copy number of AOB-amo A gene was positively correlated with soil N₂O cumulative emission(r=0.601).Under the condition of adding inhibitors,soil N₂O is mainly produced by denitrification pathway dominated by functional genes such as nirS and nirK.