| Maize/soybean intercropping is a common intercropping pattern,which plays an important role in improving land use efficiency and crop yield.However,there are few studies on the characteristics of combined straw returning and straw decomposition of intercropping and its effects on soil fertility.Aiming at the maize/soybean straw produced in intercropping mode,this study explored the combined return of straw under different nitrogen supply levels（M,maize straw alone;S,single application of soybean straw;MS,1:1 mixture of corn/soybean straw;2MS,2:1 mixture of corn/soybean straw;CK,no straw）on straw decomposition,straw nutrient release,dynamic change of soil nutrient and yield.At the same time,high-throughput sequencing technology was used to determine the soil microbial community structure,revealing the changes of soil nutrient and microbial community structure driven by straw combined returning to the field,in order to provide a theoretical basis for the technology promotion of straw combined returning to the field in the northeast black soil area.The main results of relevant studies are as follows:（1）Nitrogen application had significant effects on straw decomposition and nutrient release.The decomposition rates of S,MS and 2MS were 59.60%～64.40%,48.97%～57.43%and46.97%～55.02%in the first 40 days,respectively.However,the decomposition of M treatment was the fastest in the first 60 days,reaching 40.28%～50.29%,showing a trend of"first fast and then slow".The decomposition rate of straw treated with S,MS and 2MS at N1(110kg·hm-2)was faster than that at N0（no nitrogen fertilizer）and N2(160kg·hm-2),while the decomposition rate of straw treated with M was the fastest at N2.The decomposition rate of straw treated with S is better than that treated with M,MS and 2MS at the three nitrogen levels.（2）N,P and K of straw treated with S,MS and 2MS were released fastest at N1 level,while M treatment was released fastest at N2 level.Under N1 level,72.91%,69.73%and 69.23%of straw nitrogen,84.63%,88.13%and 89.72%of straw phosphorus,94.71%,95.44%and 91.74%of straw potassium were released under S,MS and 2MS treatment.Under N2 level,74.67%,85.59%and 88.30%of straw nitrogen,straw phosphorus and straw potassium were released under M treatment.（3）The contents of soil organic matter,ammonium nitrogen,available phosphorus and available potassium under intercropping were higher than those under monoculture,while the contents of nitrate nitrogen under monoculture was higher than that under intercropping.At N1level,the content of ammonium nitrogen and nitrate nitrogen in soil showed a gradually decreasing trend and reached the lowest value at the end of the experiment.Soil available P showed an"M"-shaped periodic change and gradually decreased,and available potassium content showed a trend of"first increase and then decrease".（4）The relative abundance of fungi in soil under intercropping was significantly higher than that under mono-cropping,but the relative abundance of bacteria was not significantly different.The relative abundance of bacteria in intercropping mode was the highest in S and MS treatment,and the highest in monocropping mode in 2MS treatment.Arthrobacter,Sphingomonas,Bacillus,RB41,Blastococcus and other bacteria that are important for nitrogen fixation and phosphorus decomposition or stalk decomposition were significantly increased.Bacteria were most significantly affected by the content of ammonium nitrogen and available potassium.There were significant differences in the composition of fungi community between the straw returning treatments under mono-cropping and intercropping.The relative abundance of Beauveria,Metarhizium,Trichoderma,Entoloma and other bacteria was significantly increased under intercropping.Fungi were most significantly affected by nitrate nitrogen.（5）The plant height,ear length,ear diameter,100 grain weight and crop yield of maize and the plant height,pod number per plant,grain number per plant,grain weight per plant,100 grain weight and yield of soybean were significantly increased when the combined maize/soybean straw returning combined with 110kg·hm-2nitrogen fertilizer was applied.In conclusion,this study identified the relative advantages of 110kg·hm-2（N1）nitrogen fertilizer combined with maize/soybean straw returning（MS,2MS）in straw decomposition and nutrient release at the three nitrogen application levels,which proved that when 110kg·hm-2nitrogen was applied,Straw decomposition was accelerated,soil nutrients were increased effectively,microbial community abundance was increased,and crop yield was increased.It is proved that corn/soybean straw combined with nitrogen fertilizer is one of the efficient fertilization modes in modern agricultural production.This experiment provides data support for the study of corn/soybean straw combined return to the field,and has important significance in exerting straw resource benefit,improving land fertility and ensuring crop stable yield. |
