| A 6-years field experiment was carried out in Maolizhuang Village,Liangcai Township,Bincheng District,Binzhou City from 2019 to 2020,with stubble return(2013-2018)and tillage measures(plowing in 2019 before irrigation and leaching in saline soil).Four treatments were set in the experiemnt: stubble non-returning to the field + rotary tillage(CT),cotton stubble non-returning + plowing(PT),cotton stubble returning + rotary tillage(SR),and cotton stubble returning + plowing(SPT).The objectives of present study were to identify influence of stubble returning and plowing on the main physical and chemical properties of soil,microbial community structure and cotton yield,providing theoretical support for the development of cotton planting in coastal saline soil,alleviating the contradiction between grain and cotton,improving cotton production capacity and ecological environment.The main results were as follows:1.The effect of stubble returning and plowing on soil aggregates and water contentCompared with stubble non-returning(CT,PT),the stubble returning(SR,SPT)significantly increased the content of > 2mm soil macroaggregates in the 0-20 cm soil layer,but significantly reduced the content of 0.25-0.053 mm microaggregates.Compared with non-plowing(CT,SR),plowing(PT,SPT)significantly increased the content of > 2mm macroaggregates of 10-20 cm soil layer.Stubble returning and plowing had no effect on the soil water content in each stage.Only the stubble returning to the field significantly reduced the water content of the 0-20 cm soil layer in the boll opening stage in 2019.2.The effect of stubble returning and plowing on soil chemical propertiesStubble returning and plowing have different influence trends on soil salt content and pH.Compared with stubble non-returning(CT,PT),stubble returning(SR,SPT)significantly reduced the soil salt content of 0-40 cm during both stages in two years and decreased the pH of the 0-20 cm soil layer during open boll stage,which had no significant effect on other soil layers in 2019.Compared with non-plowing(CT,SR),plowing(PT,SPT)significantly increased the salt content of the 0-40 cm soil layer before the two-year sowing and the 0-60 cm soil layer during boll opening stage,and the plowing had no effect on the pH.Stubble returning and plowing have different influence trends on soil organic carbon,soil dissolved organic carbon,and soil aggregate organic carbon at different growth stages.Compared with stubble non-returning(CT,PT),stubble returning(SR,SPT)significantly improved the soil organic carbon,soil dissolved organic carbon,and soil aggregate organic carbon in the 0-20 cm soil layer before sowing and during boll opening stage in two years,but had no significant effect on the indexes of the soil layer below 20 cm.Plowing has no significant effect on all indicators.Stubble returning and plowing have different influence trends on soil available nutrients at different growth stages.In the 0-20 cm soil layer,compared with stubble non-returning(CT,PT),stubble returning(SR,SPT)significantly increased the total nitrogen,nitrate nitrogen,available potassium at both years and the content of ammonium nitrogen before sowing in2019,and significantly reduced the available phosphorus content at different stages in 2020.Compared with non-plowing(CT,SR),plowing(PT,SPT)significantly increased the ammonium nitrogen content before sowing in 2019 and significantly reduced the nitrate nitrogen content during boll opening stage in 2019.Stubble returning and plowing have little effect on the content of available nutrients in other periods and soil layers.In the 20-60 cm soil layer,compared with the stubble non-returning(CT,PT),stubble returning(SR,SPT)significantly increased the ammonium nitrogen in the 20-40 cm soil layer before sowing in2019,and significantly decreased the content of available phosphorus in the 20-60 cm soil layer during boll opening stage in 2020.Stubble returning and plowing have little effect on the content of available nutrients in other stages and soil layers.3.The effect of stubble returning and plowing on the microbial structure communityThe 16 s rRNA sequencing results showed that in the 0-20 cm soil layer,compared with the stubble non-returning(CT,PT),stubble returning(SR,SPT)significantly increased the species diversity(Shannon index),richness of the soil bacterial community(Chao1 index),and the relative abundance of Proteobacteria and Pseudomonas in 2020,and reduced the relative abundance of Firmicutes and Ammoniphilus,but had no significant impact on the dominant bacteria(genus)in 2019.Plowing has no significant effect on the composition of bacterial community.Stubble returning and plowing had no significant effect on the bacterial community structure in the20-60 cm soil.Soil salt content,organic carbon,total nitrogen,available phosphorus and available potassium were important factors affecting the structure of soil bacterial communities.The results of ITS amplicon sequencing showed that compared with the stubble non-returning(CT,PT),the stubble returning(SR,SPT)significantly increased the species diversity(Shannon index),the relative abundance of Ascomycota in 2019,Basidiomycota and Fusarium in 2020,and reduced the relative abundance of Alternaria in 2020 in the 0-20 cm soil layer.Plowing significantly increased the relative abundance of Fusarium,but had no significant impact on other dominant bacteria(genus).Stubble returning and plowing had no significant effect on the composition of the fungal community in the 20-60 cm soil.Soil total nitrogen is an important factor affecting fungal diversity and dominant bacteria(genus).4.The effect of stubble returning and plowing on cotton growth and yield compositionCompared with stubble non-returning(CT,PT),stubble returning(SR,SPT)increased the plant height and the number of fruit branches of cotton,and reduced the shedding rate;plowing increased the total number of cotton nodes,but had no significant effect on plant height,fruit branches number and shedding rate.Stubble returning significantly increased the lint yield,and plowing significantly increased the of lint yield under the condition of stubble non-returning,but had no effect on lint yield under cotton stubble return.Stubble returning significantly increased the number of bolls;plowing increased the number of bolls,bolls per plant and the lint percentage,but did not reach a significant level.Stubble returning and plowing had no significant effect on cotton fiber quality. |
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