| The output of straw and livestock manure is large in China.Returning straw and organic fertilizer to the field is an effective means for comprehensive utilization of straw and livestock manure.The slow decomposition of straw returning to the field restricts the effect of straw returning to the field to improve soil fertility.It is a current research hotspot on how to promote straw decomposition to improve soil fertility.In addition,carbon and nitrogen in soil are two essential elements for crop growth,reflecting soil fertility.Water regulation,straw returning and organic fertilizer application are effective means to adjust the balance of soil carbon and nitrogen.Therefore,this paper studies the effects of straw returning combined with organic fertilizer on straw decomposition and soil carbon and nitrogen under different irrigation conditions.Taking corn,wheat straw,chicken manure compost and sandy loam soil as experimental crops,three irrigation levels were set to compare the decomposition characteristics of straw returning and straw returning combined with organic fertilizer.The effects of straw returning,organic fertilizer application and straw returning combined with organic fertilizer application on soil carbon and nitrogen under three irrigation levels were compared,and the effects of different irrigation amounts after straw returning combined with organic fertilizer application on soil carbon and nitrogen were compared.The main conclusions are as follows:（1）In the 76-day straw decomposition experiment,the decomposition of straw can be divided into two stages:The first stage is the rapid decomposition period（0～45 days）,the decomposition of straw and the release rate of carbon and nitrogen are relatively fast;The second stage is the slow decomposition period（45～76 days）,the decomposition of straw and the release rate of carbon and nitrogen are slow.Water regulation and straw returning combined with organic fertilizer can promote straw decomposition and carbon and nitrogen release,while straw returning combined with organic fertilizer and appropriate irrigation can improve the fertilization effect of straw returning.（2）From the point of view of the whole growth period of maize,at the same irrigation level,soil DOM content was significantly increased after straw returning combined with organic fertilizer compared with CK,and soil DOM content increased with the increase of irrigation amount at three irrigation levels.Under the same water level,in the corn seedling stage,caused by straw returned after priming effects lead to straw returned with organic fertilizer on soil DOM levels were significantly lower than CK,the corn big trumpet period,the grouting period,mature period,straw returned with organic fertilizer on soil DOM levels were significantly higher than that of applying organic manure treatment with CK,Under the same irrigation level,the content of DOM in soil treated by straw returning combined with organic fertilizer was always higher than that treated by straw returning in the whole growth period.Soil DOM can be divided into C1（terrestrial humic acids）,C2（protein-like acids）and C3（typical humic acids）.According to the whole growth period of maize,the relative contents of soil C1,C2 and C3 were significantly increased under the three irrigation levels compared with CK treatment.The content of C1 and C2 increased by 77.83%,86.53%and 102.57%on average（P<0.05）,and the increase rate of C1 and C2 in straw returning combined with organic fertilizer treatment was higher than that in straw returning combined with organic fertilizer treatment.In addition,the relative content of C1 and C2 increased with the increase of irrigation amount under the three irrigation levels.Under the same irrigation level,the increase of C3 by straw returning combined with organic fertilizer was different in different growth stages of maize.Under the three irrigation levels,the increase of C3 by straw returning combined with organic fertilizer was lower than that by organic fertilizer,which was 8.53%lower on average（P<0.05）,and higher than that by straw returning.The increase rate of C3was higher than that of organic fertilizer and straw returning at the big trumpet stage,filling stage and maturity stage.Under different irrigation levels,the change sequence of different fluorescence components with time was C1/C3→C2,indicating that straw returning combined with organic fertilizer could regulate the composition and structure of soil water-soluble organic matter by increasing the content of humic acid in soil.From the point of view of the whole growth period of maize,under the same irrigation level,the electronic transfer ability of soil DOM in straw returning combined with organic fertilizer treatment was significantly improved compared with CK treatment,which increased by 87.38%on average in the whole growth period（P<0.05）.At the seedling stage,the increase of electronic transfer ability of SOIL DOM of straw returning combined with organic fertilizer treatment was lower than that of straw returning,but higher than that of straw returning,and the increase of ETC of straw returning combined with organic fertilizer treatment was higher than that of straw returning and organic fertilizer treatment at the big horn stage,filling stage and mature stage of corn.In the whole growth period,the electronic transfer capacity of soil DOM treated by straw returning combined with organic fertilizer increased with the increase of irrigation amount under three irrigation levels.（3）In the whole growth period of maize,compared with CK,soil microbial carbon,nitrogen and nitrate nitrogen were significantly increased by straw returning combined with organic fertilizer under three irrigation levels,while ammonium nitrogen was significantly decreased.In addition,the contents of microbial carbon,nitrogen and nitrate nitrogen increased with the increase of irrigation amount,while the contents of ammonium nitrogen decreased with the increase of irrigation amount. |
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