Effects Of Nitrogen Management On Yield And N₂O Emission Of Fresh Corn In Hainan Province

Rational nitrogen application is an important strategy to obtain higher target yield and reduce environmental pollution caused by nitrogen.The effects of different application times and one-time application of compound fertilizer with different stability on maize yield and soil N₂O emission were studied by pot experiment in two seasons,and the relationship between the abundance of nitrogen transformation function genes and N₂O emission was discussed.The pot experiment of the first season consisted of four treatments:blank（CK,no urea）,one-time application of nitrogen(S1,0.5g·kg^-1 urea was applied to the soil once+nitrification inhibitor DCD),secondary application(S2,0.5g·kg^-1 urea was applied to the soil twice in 40%and 60%parts)and triple application(S3,0.5g·kg^-1 urea was applied to the soil in 20%,40%and 40%parts three times).The pot experiment in the second season consisted of four treatments:blank（CK,no nitrogen fertilizer）,one-time deep application of stable compound fertilizer（NAM）,one-time deep application of stable compound fertilizer（DMPP）,and one-time deep application of compound fertilizer（NMAX）.The results are as follows:（1）Soil acidification was promoted by N application,and the degree of soil acidification was significantly different with N application times.The more N application times,the stronger soil acidification was.Nitrogen application significantly increased ear yield and stem biomass of fresh table maize,but the effect of nitrogen application times on soil p H might lead to differences in the degree of nitrogen uptake and utilization.S3 treatment significantly reduced soil p H,but also reduced the accumulation of nitrogen uptake and nitrogen use efficiency of plants,resulting in high N₂O cumulative emissions.Compared with S3,the yield of S1 and S2 increased by 40.21%and 42.55%,respectively,and the cumulative N₂O emission of S1 and S2 decreased by 79.4%and 20.9%,respectively.（2）N₂O emission was significantly positively correlated with the abundance of AOB and nir K genes,and AOB and nir K were the main contributors to N₂O emission.The S1 treatment significantly decreased the abundance of AOB and nir K genes and the N₂O emission was low,while the S2 and S3 treatment significantly increased the abundance of nir K and nir S genes,decreased the abundance of nos Z genes and promoted the N₂O emission.（3）Adding NAM and NMAX compound fertilizer had no significant effect on soil acidification,but adding DMPP compound fertilizer significantly reduced soil p H value.Adding NAM compound fertilizer significantly increased ear yield and stem biomass,the crop cumulative nitrogen uptake and nitrogen use efficiency were significantly higher than those of other treatments,and the soil N₂O cumulative emission was significantly lower than that of adding NMAX and DMPP compound fertilizer.Combined with various indicators,NAM stable compound fertilizer has the best effect,which can not only guarantee maize yield,improve nitrogen use efficiency,but also significantly achieve N₂O emission reduction.（4）The dynamic changes of AOB,nir K and nos Z gene copy number were basically the same after the application of compound fertilizer with different nitrogen synergist.N₂O emission was significantly positively correlated with the abundance of AOB and nir K genes,and negatively correlated with the copy number of nos Z gene.With the increase of AOB and nir K gene copy number,soil N₂O emission flux gradually increased and reached the peak value.At the later stage of culture,the increase of nos Z gene copy number in soil made N₂O reduced more thoroughly,and N₂O emission decreased and tended to be flat.（5）Therefore,nitrogen application times affect the functional genes of nitrogen transformation process,and thus affect N₂O emission.The one-time application of urea combined with DCD could be the recommended fertilization mode in the cultivation process of fresh corn in Hainan.Nam compound fertilizer can be used as the recommended fertilizer for fresh corn one-time fertilization in Hainan hot area.