Effects Of Exogenous Carbon And Nitrogen And Straw Return To Field On Soil Enzyme Activity And Carbon Fraction And Rice Yield

Rice straw is rich in elements and organic nutrients.If it can be returned to the field efficiently,rice straw will be an important source of nutrition for the growth and development of rice.However,rice straw had the high C/N and the decomposition is slow.At the same time,the rice straw return the field will stimulate the vigorous activities of microorganisms,resulting in the phenomenon of competing with crops for nitrogen,thus affecting the growth and development of rice.Therefore,exogenous carbon and nitrogen were added to adjust the high C/N ratio of rice and promote the decomposition of rice straw.In this experiment,the characteristics of changes in soil nutrients,soil enzyme activities and soil organic carbon fractions after adding exogenous carbon and nitrogen to rice straw were investigated by an indoor simulated incubation experiment,and the effects of rice straw with nitrogen on rice yield and composition factors were studied by a field experiment.Among them,both the indoor simulated incubation test and the field experiment were conducted on the soil of paddy field in Brilliant Village,Longfeng Township,Wuchang City.A total of eight treatments were set up for the indoor simulated culture experiment:control（S0N0T0）,straw（S1N0T0）,additional carbon source（S0N0T1）,additional nitrogen source（S0N1T0）,additional carbon and nitrogen（S0N1T1）,straw+exogenous carbon（S1N0T1）,straw+exogenous nitrogen（S1N1T0）,and straw+exogenous carbon and nitrogen（S1N1T1）.A total of four treatments were set up for the field experiment:conventional fertilizer（S0D0）,straw（S1D0）,straw+nitrogen fertilizer（S1D1,S1D2）for a total of 4 treatments.Soil nutrients,soil enzyme activity,organic carbon components and rice yield were systematically measured and analyzed.This study is to provide a meaningful research theoretical basis for the efficient utilization of straw in the future.To provide a meaningful theoretical basis for the efficient utilization of rice straw resources.The test results were as follows:（1）After the addition of exogenous carbon and nitrogen to rice straw,the alkaline nitrogen and available phosphorus contents of all treatments showed a trend of increasing and then decreasing with increasing incubation time.The alkaline nitrogen content reached its peak at the 30th day of incubation.The peak of available phosphorus content was reached at the 60th day.Compared with other treatments,S1N1T1 treatment showed the highest alkaline nitrogen and available phosphorus content,were 310.67mg·kg^-1 and 87.33mg·kg^-1,respectively,reaching a significant level of difference（P<0.05）;available potassium content showed a gradual increase with the extension of incubation time.S1N1T1 treatment showed the highest available potassium content of 244.30mg·kg^-1 and significantly higher than other treatments（P<0.05）.The organic carbon content showed an“N”-shaped trend,and compared with the S0N0T0 treatment,the S1N1T1 treatment had the highest organic carbon content of 24.97g·kg^-1,which was significantly higher than other treatments（P<0.05）.（2）After the addition of exogenous carbon and nitrogen of rice straw,the urease activity,sucrase activity and cellulase activity of all treatments showed an increasing trend followed by a decreasing trend with the increase of incubation time.The soil urease activity and sucrase activity of each treatment reached the highest level on the 30th day of incubation.The soil cellulase activity reached the peak at the 60th day of incubation.Compared with other treatments,S1N1T1 treatment had the highest content for urease activity,sucrase activity and cellulase activity,which were1.01mg·g^-1·24h^-1,3.80mg·g^-1·24h^-1 and 0.93mg·g^-1·72h^-1,respectively and reaching a significant level of difference（P<0.05）.S0N0T1 treatment could significantly enhance sucrase activity.S0N1T0 treatment could significantly increase the urease activity.（3）After rice straw combined with exogenous carbon and nitrogen,the trends of total humic acid carbon and free humic acid carbon were completely consistent in inert organic carbon,showing a trend of first increase and then decrease.Among all the treatments,S1N1T1 treatment showed the highest total humic acid carbon and free humic acid carbon content of 10.33mg·g^-1 and 7.99mg·g^-1,respectively,which were significantly higher than the other treatments（p<0.05）;in the active organic carbon,the content of easily oxidized organic carbon showed a gradual increase trend with the extension of incubation time,and compared with the S0N0T0 treatment,S1N1T1 treatment had the highest soil oxidizable organic carbon content,which was 1.24mmol·g^-1,reaching a significant level of difference（p<0.05）;in the active organic carbon,the microbial carbon,neutral sugar and dissolved organic carbon content showed a trend of increasing and then decreasing with the extension of incubation time.The microbial carbon and dissolved organic carbon contents reached a peak on the 60th day,and the neutral sugar content reached a peak on the 30th day.Compared with other treatments,S1N1T1 treatment had the highest content for microbial carbon,neutral sugar and dissolved organic carbon,which were 5.00mg·kg^-1,308.46μg·g^-1and 6.77mg·g^-1,respectively,and significantly higher than other treatments（p<0.05）.（4）The analysis of the effects of rice straw and exogenous carbon and nitrogen on soil nutrients,enzyme activities and organic carbon fractions showed that rice straw,exogenous carbon and nitrogen and their interactions all had significant or highly significant effects on each index;the best treatment was S1N1T1 treatment,as ranked by the composite score of principal component analysis.（5）Rice straw with Nitrogen return to the field treatment（basal tiller fertilizer:spike fertilizer=6.5:3.5）had the highest rice spike number,spike grain number,fruiting rate,thousand grain weight and yield,which increased by 90.01%,29.85%,58.17%and 27.53%,respectively,compared with the S0D0 treatment,reaching a significant level of difference（p<0.05）.The next was S1D2treatment（basal crop fertilizer:spike fertilizer=8:2）,rice yield was 5.49 t·hm^-2.In summary,the principal component analysis of the indices measured in the indoor culture test showed that S1N1T1 treatment was the optimal treatment;the field test showed that the rice straw with nitrogen return to the field treatment（basal crop fertilizer:spike fertilizer=6.5:3.5）,the rice yield was the highest.