Effects of biochar combined with nitrification inhibitor(DMPP)on reducing NH3 and N2O emission in paddy soil and its microbial mechanism
[Objectives]The effect and mechanism of biochar and nitrification inhibitor on reducing the emission of main active nitrogen gas in paddy was studied to evaluate the mitigation effects of single or combined application of biochar and nitrification inhibitor.[Methods]A typical paddy soil was collected in Zhejiang Province for a potted experiment inside the airtight boxes.Five treatments were set up:no nitrogen fertilizer(N0),urea(Urea),urea+nitrification inhibitor(DMPP),urea+biochar(BC),urea+nitrification inhibitor+biochar(BCDM).Gas chromatography and Drage-Tube method were used to monitor soil N2O and NH3 emissions during crop growth.After basal,tillering and panicle fertilization,the surface and leakage water were sampled for measuring inorganic N concentrations.After rice harvest,fresh soil samples were collected to extract soil microbial DNA for determing the number of key functional microorganisms(AOB,AOA and nosZ),using qPCR technology.[Results]After base fertilization,all the treatments did not increase NH4+-N concentration in surface water significantly.After tillering and panicle fertilization,BC and DMPP treatments significantly increased NH4+-N concentration in surface water up to 35.4 mg/L,while BCDM and DMPP treatments reduced NO3--N concentration in surface water by 80.0％and 56.9％.Compared with Urea treatment,BC and DMPP alone or combined application significantly reduced the cumulative N loss in surface water,with the highest reduction 95.6％in BCDM.The cumulative N leakage loss at 20 cm and 40 cm soil depth was 3.67 kg/hm2 in Urea,which were reduced by 16.5％,27.9％and 37.4％in BC,BCDM and DMPP treatments,respectively.BC,DMPP and BCDM treatment also significantly reduced the cumulative N2O emission by 31.5％,64.0％and 57.6％,respectively.DMPP significantly increased ammonia cumulative emission by 10.5％,while BC combined with DMPP or BC alone decreased ammonia cumulative emission by 25.2％and 21.6％.During the growth period of rice,the indirect N2O emission caused by NH3 emission accounted for 83.9％,90.2％,90.5％,52.9％and 82.0％of the total N2O emission in BC,BCDM,DMPP,N0 and Urea treatments,respectively.qPCR results showed that compared with Urea treatment,BC and DMPP alone or combined application significantly increased the amoA gene copy number of AOA by 48.0％-73.4％,and decreased the amoA gene copy number of AOB by 62.7％-195.6％;DMPP alone or combined with BC increased the copy number of nosZ gene by 3.7％-14.8％,thus promoting the N2O reduction ability,and reducing N2O emission.[Conclusions]During rice growing period,the combined application of biochar and DMPP can significantly reduce the copy number of amoA-AOB gene in soil,decrease the nitrification process,and reduce NO3-N concentration,thus reduce the inorganic nitrogen loss in surface and leakage water.At the same time,the combined application of biochar and DMPP can increase the copy number of N2O reductase nosZ gene,which is a key function of active nitrogen gas production process,thus decline the total emission of N2O(N2O direct emission and NH3 indirect emission)by 32.2％,suggesting that the combination is an effective way on the reduction of N2O emission and NH3 volatilization.
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