Effects Of Water Regulation Under Subsurface Drainage On Root-Zone Soil Microenvironment,Yield And Quality Of Sunflower

Soil salinization is serious and water shortage are the main limiting factors affecting the agricultural development in Hetao irrigated area.Irrational irrigation system leads to low utilization rate of soil water and fertilizer,serious secondary salinization of soil and imbalance of microbial community structure,which affects crop yield and quality.In this study,a field experiment was conducted in the salinized farmland located in Hetao Irrigation District from 2020 to 2021 to study the effects of water regulation under subsurface drainage on soil desalting effect,soil microenvironment in sunflower root zone and yield and quality,and to reveal the internal influencing mechanism among soil physical and chemical properties,microbial community structure and yield and quality of sunflower.Finally,entropy weight TOPSIS comprehensive evaluation method was used to determine the appropriate irrigation volume under dark pipe drainage.The results of this study are of great significance for realizing efficient water saving and salt control,increasing crop yield and improving soil ecological environment in irrigated areas.The main research results are as follows:(1)Under subsurface drainage,the desalting effect of 330 mm irrigation was the best,and the desalting rate was 11.45% higher than that of 210 mm irrigation,120 mm irrigation and no drainage treatment.With the same irrigation amount,the desalting rate of subsurface drainage increased by 13.54% compared with that of no drainage treatment.Compared with no drainage treatment,subsurface drainage treatment reduced soil moisture content,increased the leaching of nutrients in soil,and raised soil temperature.The nitrogen content was the highest in the 210 mm treatment,which not only ensured the dissolution of nitrogen in soil,but also did not cause a large amount of nutrient leaching.(2)Under subsurface drainage,the irrigation water of 210 mm increased the soil microbial diversity,and also increased the relative abundance of Proteobacteria,Chloroflexi,Acidobacteria in soil bacteria,Ascomycota and Mortierellomycota in soil fungi.Water content,temperature,p H,EC and nitrate nitrogen were the key environmental factors affecting bacterial community diversity,while temperature,ammonium nitrogen and nitrate nitrogen were the key environmental factors affecting fungal community diversity.Water content,EC and ammonium nitrogen content were the main physicochemical factors affecting the distribution of bacterial community structure.Water content,temperature and EC were the most important physicochemical factors affecting the distribution of fungal community structure.(3)Compared with no drainage treatment,the yield of treatments under subsurface drainage increased by 32.37% on average,the 100 grain weight increased by 14.44% on average,and the seed setting rate increased by 5.3% on average.Under subsurface drainage,the production efficiency of 120 mm irrigation water was the highest,which was increased by 1.64,0.79 and 1.91 units compared with the other three treatments,the nitrogen offset productivity of 330 mm irrigation water was the highest,which was increased by 3.19,6.81 and 7.24 units compared with the other three treatments.The irrigation amount of 210 mm was the most beneficial to the synthesis of protein and essential amino acids.(4)Principal component analysis and subordination function evaluation were used to comprehensively evaluate 13 yield and quality indexes of each treatment,such as yield,100 grain weight,seed setting rate,dry weight per plant,crude fat,protein,7 essential amino acids,and the two evaluation methods obtained the highest comprehensive score of irrigation quantity 210 mm under subsurface drainage,which was the best yield and quality irrigation treatment.(5)Based on TOPSIS model of entropy weight method,a comprehensive evaluation was carried out on 15 indexes such as soil desalting rate,soil microbial diversity,water and nitrogen utilization rate,and sunflower yield and quality of each water treatment in subsurface farmland.The highest comprehensive score was determined that the irrigation volume under subsurface drainage was 210 mm.The treatment achieved efficient water saving and salt control,increased yield and quality,it also improves the farmland ecological environment and is conducive to the sustainable development of agriculture.It is the irrigation treatment with the best comprehensive improvement effect.