| Straw returning is the main way of soil organic fertilization,and its decomposition and transformation is a prerequisite for the formation of soil humus.It is necessary to understand the decomposition and humification characteristics of returning straw to study the change of soil humus content and the degree of humification.The study used different nitrogen levels starting in 2013(T1:no nitrogen application;T2:75 kg/hm2;T3:150 kg/hm2;T4:225 kg/hm2;T5:300 kg/hm2;T6:375 kg/hm2)based on the long-term positioning test,the nylon net bag method was used,and the same amount of corn straw was returned to the field for comparison with the treatment of non-returning field,and the cumulative decomposition of the same amount of corn stover under the condition of different nitrogen fertilizers for 6 years was studied.Rate,nutrient release rate and its effects on soil humus,humic acid(HE),humic acid(HA),fulvic acid(FA),humin(HM)content and humification degree after returning to field.The main test results are as follows:1.The application of different nitrogen levels significantly affected the pre-decomposition and carbon and nitrogen release of returning straw,and had no significant effect on the release of phosphorus and potassium;Under the conditions of this experiment,the decomposing of corn stalk mainly occurred in the first 90 days after returning to the field,the cumulative decomposing rate increased rapidly,and increased with the increase of nitrogen application rate,and treated with T5 with nitrogen application rate of 300 kg/hm2.The highest,the difference between treatments was significant(P<0.05);the release rate of carbon and nitrogen in straw was consistent with the change of cumulative decomposing rate,while the release rate of phosphorus and potassium was not related to the amount of nitrogen applied;corn stalk returned to field for 150 days.After that,the cumulative decomposing rate was 52.7%～55.8%,and the nutrient release was K>C>P>N.2.Returning straw can not only increase the content of HE and HA in soil under the condition of low nitrogen application(75～150 kg/hm2),but also increase the degree of soil humification;while applying nitrogen in high amount(300～375 kg/hm2)under the condition of straw returning is beneficial to the increase of soil total organic carbon(TOC),FA and HM,but it is not conducive to the improvement of soil humification;Straw returning increased the content of TOC,HE,HA and HM in soil,reduced the content of FA in soil and increased the degree of humification(HR,HA/FA,PQ).However,the soil TOC content increased with the increase of nitrogen application rate in different treatments,and the highest was 11.20 g/kg treated with T5.The application of nitrogen content was 150 kg/hm2,which contributed to the increase of soil HE content,and the remaining nitrogen application conditions.The lowering of the HE content has an inhibitory effect.When the nitrogen application rate is 300 kg/hm2,the inhibition effect is significant(P<0.05).When the nitrogen application rate is 75～225 kg/hm2,the soil HA content can be increased.When the nitrogen application rate was 150 kg/hm2,the HA content was the highest,and the nitrogen application rate higher than 225 kg/hm2 was not conducive to the increase of soil HA content.Compared with no nitrogen application,only the soil nitrogen content of 375 kg/hm2 was higher than that of no nitrogen treatment.Under the condition of nitrogen application rate of 150 kg/hm2,the straw returning to the field reduced the soil HM content,and the rest of the soil applied nitrogen increased the soil HM content.The nitrogen content of the nitrogen application in the field was higher than that without nitrogen treatment,where T5 treatment was the highest(P<0.05).The HA/FA and PQ values in the returning soil were the highest under T2 treatment,and then decreased with the increase of nitrogen application rate.The HA/FA and PQ values of T6 treatment were significantly lower than other treatments(P<0.05),but the application of nitrogen fertilizer was Straw returning to soil with 75 kg/hm2 to 300 kg/hm2 has a tendency to increase soil HA/FA and PQ values.The soil HE/TOC(HR)was 35.82%in the no nitrogen treatment,which was significantly higher than other treatments(P<0.05).Straw returning reduced soil HM/TOC,and nitrogen application was significantly higher than no nitrogen treatment,and T5 treatment was the highest(P<0.05).3.Under the condition of applying nitrogen fertilizer of 300 kg/hm2,straw returning increased the molecular activity of soil HA,decreased the molecular weight and aromatization degree of HA,and made soil HA easier to simplify;Except for T3 treatment,the straw returning to the field reduced the E4/E6 value and Alog K value of soil HA under the other nitrogen application conditions,and the value increased under the condition of nitrogen application rate of 300 kg/hm2,indicating that Under the condition of high nitrogen content(300 kg/hm2),the return of straw to soil reduced the molecular weight of soil HA,the degree of aromatization decreased,and the molecular activity was improved.However,the molecular activity of soil HA was inhibited under other nitrogen application conditions.4.Applying different amounts of nitrogen fertilizer to reduce soil pH,increase soil nitrate nitrogen,available phosphorus,available potassium and potato yield,but had no significanteffect on soil ammonium nitrogen content.The content of nitrate nitrogen in the soil increased by 41.56%～97.13%after the strawwas returned to the field,and the ammonium nitrogen content did not change significantly.Compared with non-returning field,straw returning increased the soil available phosphorus content by 5.60%～13.85%,and the soil available phosphorus content of T5 treatment was the highest(41.02 mg/kg),but there was no significant difference between treatments,indicating different application.Nitrogen content had no significant effect on soil available P content.Compared with the non-returning field,the available potassium content in the field was significantly increased by 10.70%～24.09%.There was no significant difference in the treatments,indicating that nitrogen application had no significant effect on the soil available potassium content.Straw returning reduced soil pH and there was no significant difference between treatments.Compared with the non-returning field,the potato treatment yield increased by 3.0%～24.7%,the maximum increase was not applied by nitrogen treatment,and the yield of T2 treatment was the highest.In summary,the application of nitrogen under the conditions of this experiment can significantly promote the decomposing of straw returning,and thus increase the content of soil humus;when the nitrogen application rate is 75～150 kg/hm2,the returning of straw is more conducive to the degree of soil humification.Increase. |
PDF Full Text Request