Effects Of Cotton Straw Returning And Subsoiling On Physiological Basis Of Cotton Yield Formation In Coastal Saline Soil

The experiment was carried out at Maoli village,Liangcai township,Binzhou city,Shandong Agricultural University cotton research base from 2017 to 2018.The experiment was based on the four-year straw returning experiment?2013-2016?and one-year subsoiling experiment?post-harvest cotton harvest in 2014?.Four treatments were set up:straw non-returning+non-subsoiling?CT?,straw non-returning+subsoiling?ST?,straw returning+non-subsoiling?SR?and straw returning+subsoiling?SRT?.The effects of straw returning and subsoiling on soil physical and chemical properties,soil salt ion content,cotton growth,dry matter accumulation and distribution,plant salt ion content and cotton yield were studied.Based on the improvement of soil physical and chemical properties by returning cotton straw and subsoiling,the regulation of soil-plant in coastal saline-alkali land was studied,and the theoretical support for the sustainable development of cotton in coastal saline-alkali land was provided in order to realize the sustainable development of cotton in coastal saline-alkali land.The main results are as follows:1.Effects of straw returning and subsoiling on physical and chemical properties of soilStraw returning improved the physical structure of soil surface layer for two years,and no significant effect of subsoiling was found.Straw returning?SR,SRT?significantly reduced the bulk density of 0-20 cm soil layer and 0.25-0.053 mm aggregate content in 2018 20-30 cm soil layer,and increased the content of 0-10 cm soil layer>2 mm aggregate in 0-10 cm soil layer;subsoiling?ST,SRT?increased the aggregate content of 0.5-0.25 mm in 10-20 cm soil layer and 0.25-0.053 mm in 10-30 cm soil layer.The effects of straw returning and subsoiling on soil chemical properties were as follows:0-20 cm soil layer,straw returning significantly increased the content of soil organic matter,but subsoiling had no significant effect on it.In 0-40 cm soil layer,straw returning?SR,SRT?increased the contents of total nitrogen,nitrate nitrogen,ammonium nitrogen and available potassium,and decreased the content of available phosphorus;subsoiling?ST,SRT?increased soil available phosphorus content,decreased soil total nitrogen content and available potassium content in 2018.In 40-60 cm soil layer,straw returning?SR,SRT?increased soil total nitrogen and available potassium content;and subsoiling?ST,SRT?had no significant effect on soil nutrients.The two-year trend is basically the same.In the two-year experiment,the effects of straw returning and subsoiling on soil pH and salt ion content were as follows:in 0-20 cm soil layer,straw returning?SR,SRT?increased K⁺content in soil,decreased pH,salt content,Na⁺and Cl^-content in 2017;and subsoiling?ST,SRT?increased the contents of pH,Na⁺,Cl^-in 2017.In 20-40 cm soil layer,straw returning?SR,SRT?increased the content of K⁺,Ca²⁺and Mg²⁺in soil,decreased pH,salinity,Na⁺,Cl^-contents in 2017;and subsoiling?ST,SRT?increased pH,Na⁺,Cl^-contents in 2017.In 40-60cm soil layer,straw returning?SR,SRT?increased the contents of K⁺,Mg²⁺,Ca²⁺and decreased the contents of pH and Cl^-in 2017;and subsoiling?ST,SRT?increased Cl^-content,decreased K⁺,Mg²⁺,Ca²⁺content.All treatments had no significant effect on pH,salinity,Na⁺,Cl^-contents in 2018 and HCO₃^-,SO₄^2-content in two years.2.Effects of straw returning and subsoiling on cotton growth,dry matter and nutrient accumulation and distributionWith the development of growth period,straw returning?SR,SRT?increased the plant height,total fruit node knots,leaf area index and net photosynthetic rate of cotton at flowering and boll stage;and subsoiling?ST,SRT?had no significant effect on agronomic characters and photosynthetic characteristics at each stage.Straw returning and subsoiling increased the accumulation of dry matter and total nitrogen,total phosphorus and total potassium,and the overall performance was SRT>SR>ST>CT.The increase of straw returning treatment was higher than the subsoiling treatment in two years,but in 2018 the increase of nutrient accumulation in vegetative organs by subsoiling decreased.3.Effects of straw returning and deep loosening on salt ion absorption of CottonThe absorption of cation by straw returning and subsoiling in different parts of cotton plant was different.During the two-year experiment,straw returning?SR,SRT?increased the K⁺and Ca²⁺contents of cotton stems,branches and leaves,and decreased Na⁺and Mg²⁺contents.Subsoiling?ST,SRT?increased the content of Na⁺and Mg²⁺in leaves at flowering and boll stage,and decreased the content of Mg²⁺in stems and branches at seedling,bud and early flowering stage,but had no significant effect on K⁺and Ca²⁺contents.For cotton buds and bolls,straw returning reduced Na⁺content,but had no significant effect on other ions content;subsoiling had no significant effect on ion content.4.Effects of straw returning and subsoiling on cotton yield and fiber qualityStraw return and subsoiling increased the yield of cotton for two years.The whole performance was SRT>SR>ST>CT.The main reasons for the increase of yield were the increase of total boll number and boll weight.Straw returning?SR,SRT?significantly increased the total boll number and single boll weight of cotton,and subsoiling?ST,SRT?significantly increased the total boll number of cotton in the third year after tillage,but there was no significant difference in the fourth year,and had no significant effect on the single boll weight in the two years.All treatments had no significant effect on lint percentage and fiber quality.