The Effect Of Biochemical Inhibitor On Nitrogen Transformation In Paddy Field And Its Mechanism

Nitrogen (N) fertilizer is easily lost in paddy fields, leading to a low efficiency. The application ofslow/controlled release fertilizer is considered an effective measure to solve the problem. At present,however, the types of slow/controlled release fertilizer are scarce for paddy fields. Taking the ureaseinhibitor (N-(n-butyl) thiophosphric triamide, NBPT) and nitrification inhibitor (3,4-dimethylpyrazolePhosphate, DMPP) as the experimental materials, the effects of biological inhibitors on Ntransformation in paddy field was investigated using15N tracer method. We also studied the potential ofreducing N fertilizer application when urease inhibitor was present, and the reasonable proportion ofurease inhibitor to N fertilizer, and the characteristics of soil N supply when combined application ofthe urease inhibitor and nitrification inhibitor. In addition, the influences of NBPT and DMPP on soilmicrobial community and the diversity of the functional organisms involving N cycling are alsoexplored by using molecular ecology methods and techniques. The main findings are as follows:(1) The results of stable isotope15N-traced urea showed that the addition of NBPT or combinedaddition of NBPT and DMPP can significantly increased the recovery of applied N in the above-groundparts and soil residual N. Compared to the urea treatment, the peak of volatilization and cumulative lossof NH3from the treatment added with NBPT were significantly reduced by27.04%and21.65%,respectively, and those from the treatment added with combination of NBPT and DMPP were markedlydecreased by12.95%and13.58%, respectively. On the contrast，adding DMPP alone enhanced thepeak of NH3volatilization by23.61%, the NH3losses did not increase significantly. In summary, theeffects of urea added with urease inhibitor or combination of urease and nitrification inhibitors are betterthan urea added with nitrification inhibitor alone, in view of reduction of NH3volatilization in paddyfields.(2) The results showed that N2O flux was higher in the first7days after fertilization, and theapplication of DMPP markedly reduced the N2O flux. However, the flux sharply increased after63dayspost-fertilization at mature stage of rice, especially in the treatment where inhibitor was present. Thetwo treatments added with DMPP can significantly reduce the N2O emission in the first21days afterfertilization, but cannot change total emission.(3) The results of field experiment reveal that urea of135kg N/ha added with <1%NBPT did notmarkedly increase the yield, but the addition of NBPT ranged from1%to1.5%could significantlyimprove the rice yield and recovery of applied N in the above-ground parts. Compared with the normalurea rate of180kg N/ha, the grain yields are increased by8.54%and12.87%in early and late rice, therecovery of applied N improved by6.78%and9.46%, respectively, and25%of N fertilizer can besaved as a result. Our results showed that addition of DMPP (1%) did not markedly increase the yield.But combined application of NBPT and DMPP could significantly improve rice yield and nitrogenrecovery efficiency. (4) Compared to urea treatment, the addition of NBPT notably reduced urease activity and NH+4-Ncontent at tillering stage, but enhanced the NH+4-N content and maintained the a similar activity ofurease at booting stage, revealing that the role of urease inhibitor NBPT was active before booting stage.Stepwise regressions analysis revealed that grain yield of rice was significantly associated with soilNH+4-N content at tillering and booting stage, especially the latter. Therefore, the remarkableimprovement of soil NH+4-N content at booting stage seemed to a key factor which leaded to decreaseof N fertilizer by25%and a significant yield increase in the treatment added NBPT.(5) The PLFA analysis showed that addition of NBPT or DMPP significantly decreased the totalPLFA and content of saturated fatty acids and hydroxy fatty acids, some of which were bacteria markers.However, this inhibiting effect of biological inhibitors was not found at booting stage, and a higher totalPLFA was obversed when both NBPT and DMPP were added to urea. Thus, the influence of biologicalinhibitors on microbial community mainly focused on the period before booting stage.(6) The result of quantitative PCR showed that archaeal amoA gene copy numbers were moreabundant than AOB by6~10times. However, nitrification inhibitor (DMPP) mainly affected theabundance of AOB. The abundance and community of AOA were not affected by N fertilizer at bothtillering and booting stage. These data showed that DMPP inhibited the soil nitrification throughlimiting the growth of AOB. The profile of DGGE indicated that Nitrosomonas and Nitrosospira wasdominant flora of AOB in paddy soil. N fertilizer increased the diversity of AOB and denitrifyingbacteria. The effects of NBPT and DMPP on the community of AOB were smaller than that of Nfertilizer.