| Straw return is one of the most important soil fertility measures in China.The decomposition products of straw can form soil humus.The decomposition and humification of straw returning are affected by nitrogen application rate.The study was conducted in a long-term different nitrogen fertilization;0 kg/hm~2(N0),75 kg/hm~2(N75);150 kg/hm~2(N150),225 kg/hm~2(N225),300 kg/hm~2(N300),and 375 kg/hm~2(N375)field with nylon mesh bags to study the effects of different nitrogen application rates on the decomposition characteristics of maize straw and soil humus content.And we studied the effect of returning corn stalks to the soil on the changes of soil lignocellulose and humus content under the different and other soil organic carbon conditions caused by the addition of different amounts of organic fertilizer(CK:no fertilizer;M1:organic fertilizer 1.5g/kg;M2:organic fertilizer 6.0g/kg;M3:organic fertilizer 11.5g/kg).The main results are as follows:1.Nitrogen rate significantly affected the decomposition characteristics of the maize straw returned to the soil.The straw decomposition mainly occurs in the first 90 days after burying nylon net bag,and the cumulative decomposition rate increased with increasing nitrogen application rate.Treatment N375 produced the highest cumulative decomposition rate(69%).The content of cellulose and hemicellulose in straw decreased with time,whereas the lignin content showed an opposite trend.At 150 days after straw return,the decomposition rate of hemicellulose,cellulose and lignin were 74%,36%and 65%,respectively.Treatment N375 recorded the highest hemicellulose and lignin contents,while treatment N150 had the highest cellulose content.2.Nitrogen application rate significantly affected soil humus and its components.The total humus and humin(HM)content in the soil increased with time.The fulvic acid(FA)content was inversely proportional to the content of humic acid(HA).At 150 days after straw return,total humus,HM,FA and HA increased by 113%,107%,82%and 129%,respectively.The content of HA was significantly higher than that of the FA.Treatment N150 and N300 produced the highest content of soil humus.3.Returning straw to the field significantly increased the content of humus in the soil.Compared to S0,S1 significantly increased the total humus(114%),HA(131%),FA(1025%)and HM(128%).Treatment N225 had the highest total humus and HM contents whereas treatment N300 and N0 recorded the highest FA and HA contents.4.Nitrogen rate significantly affected the concentration of lignocellulose in the soil.The content of hemicellulose in the soil decreased with time,while the content of cellulose and lignin increased.The highest content of hemicellulose(66%),cellulose(141%)and lignin(160%)were recorded at 120 days after straw return.Compared with S0,S1 significantly decreased hemicellulose and lignin content;however,the content of cellulose was significantly increased.5.Straw return significantly affected soil humus and its components.The total humus and HM increased with time whereas FA and HA decreased with time.Compared to their initial content,total humus,HM,FA and HA concentrations increased by 159%,234%,37%and 470%,respectively at 120 day after straw return.The content of HA was significantly higher than that of the FA.With the exception of FA,M3 produced significantly higher total humus,HM and HA than the control.Compared to S0 treatment,S1 treatment significantly increased the contents of total humus,HM and FA;however,the HA content decreased.M1 treatment increased the content of total humus,HM,and HA by 23%,21%and 67%,respectively whereas M3treatment increased the content of FA by 205%,followed by the M1 treatment.6.There was a positive correlation between straw decomposition and soil humus content.The content of straw lignin under different nitrogen application rate was significantly correlated with the total humus content in the soil;soil total humus content significantly correlated with HM;and FA content significantly related to HA content.Total humus significantly correlated with lignin content and hemicellulose content.Moreover,the cellulose content significantly correlated with HM content.There was a significant positive relationship between total humus and HM;however,FA content showed a negative correlation with HA content.In summary,decomposition of straw returned to the field was mainly in the early stage of returning to the field,and the application of nitrogen fertilizer and the organic fertilizer affect straw decomposition process in the soil.The application of 150 kg/hm~2or 300 kg/hm~2 of nitrogen with 1.5g/kg of organic fertilizer stimulated the accumulation of soil humus content. |
