Effect Of Biochar On Soil Improvement In Saline Water Drip Irrigation Cotton Field

?Object?The low basic fertility level of soil,shortage of fresh water,and soil salinization are the limiting factors of farmland in arid area.In view of the practical problems of saline water irrigation in arid areas,this study explored the effect of biochar and straw application on soil improvement of cotton field under saline water drip irrigation through long-term field location experiment,it provides a theoretical basis for the rational utilization of saline water resources,soil fertilizer cultivation and sustainable development of agriculture in arid areas.?Method?This study was conducted on the basis of a long-term saline water irrigation field experiment,used a 2×3 completely randomized block design with two levels of irrigation water salinity[0.35 and 8.04d S·m^-1,respectively referred to as fresh water(FW),and saline water(SW)]and three organic materials(control,cotton straw,and cotton straw biochar,respectively referred to as CK,ST,and BC),the dose of organic carbon addition of biochar was equivalent to straw returning to the field(the amount of straw application was 6 t/hm²,and biochar was 3.7 t/hm²).The fixed-position field experiment focused on the effects of biochar on(1)the distribution and movement of soil water and soil salt;(2)soil physical and chemical properties;(3)soil enzyme activity,soil microbial biomass,bacterial community structure diversity;and 4)cotton growth,nutrient uptake,and yield in saline water drip irrigation cotton field,to clarify the effect of biochar on the improvement of saline water drip irrigation cotton field soil.?Result?(1)The application of biochar and straw reduced the salt content in the surface soil of cotton field,resulting in the salt leaching to the deep layer.Salt mainly accumulated in the 40-100 cm soil layer,especially in the saline water irrigated soil.The results showed that biochar and straw application increased soil water content in 0-100 cm soil layer of cotton field under saline water irrigation;soil bulk density,water content and salinity under saline water irrigation treatment were 5.59%,50.28%and 690.77%higher than those under fresh water irrigation treatment,respectively,but saline water irrigation significantly reduced soil porosity and p H value.Biochar application significantly reduced soil salinity and bulk density,and increased soil porosity.Soil total carbon,total nitrogen,available phosphorus,and available potassium under biochar application treatment were 10.80%,5.06%,126.88%,and 11.17%higher than those under the control,respectively.(2)Soil microbial biomass C,N,and basal respiration under saline water irrigation were 16.59%,27.69%and 41.78%lower than those under fresh water treatment,respectively.Meanwhile,saline water irrigation significantly reduced soil microbial quotient and metabolic quotient.Biochar and straw application significantly increased soil microbial biomass carbon,nitrogen and basal respiration.To a certain extent,biochar and straw application increased soil microbial quotient and metabolic quotient,but there was no significant difference in soil microbial quotient and metabolic quotient under saline water irrigation treatment.Saline water irrigation promoted the activities of urease,nitrate reductase,nitrite reductase and hydroxylamine reductase,but inhibited the activities of sucrase,?-glucosidase and polyphenol oxidase.Under saline water irrigation treatment,biochar and straw application significantly increased the activities of sucrase,?-glucosidase,cellobiase and polyphenol oxidase;however,biochar application significantly decreased the activities of urease,nitrate reductase and hydroxylamine reductase;straw application increased the activities of nitrate reductase,nitrite reductase and hydroxylamine reductase.(3)Biochar application increased the number of OTUs of bacteria.Saline water irrigation decreased bacterial Ace and Chao1 index,but increased Shannon index.Under saline water irrigation,biochar application increased Shannon index of bacteria to a certain extent,while straw application significantly decreased Ace and Chao1 index of bacteria.The dominant phylum of soil bacteria in different treatments were Proteobacteria,Acidobacteria,and Actinobacteria.(4)Compared with fresh water irrigation,saline water irrigation reduced the relative abundance of Proteobacteria,Acidobacteria,and Actinobacteria.Biochar and straw application increased the relative abundance of Proteobacteria,but biochar application decreased the relative abundance of Acidobacteria;Saline water irrigation decreased the relative abundance of RB41,Arthrobacter and dongia,but increased the relative abundance of Sphingomonas and Nitrosospira;biochar and straw application increased the relative abundance of Sphingomonas and Arthrobacter,decreased the relative abundance of RB41,and straw application also increased the relative abundance of dongia.(5)Compared with fresh water irrigation,the growth of cotton was inhibited under saline water irrigation treatment,and the plant height and biomass of cotton were significantly reduced.At the same time,saline water irrigation inhibited the uptake of nitrogen,phosphorus and potassium in cotton,and ultimately reduced the yield of cotton and the use efficiency of irrigation water.Regardless of whether it is fresh water or salt water irrigation,straw and biochar returning can promote cotton growth,increase cotton plant height and biomass.At the same time,the application of straw and biochar also significantly increased the uptake of nitrogen,phosphorus and potassium,and then increased cotton yield and irrigation water use efficiency.?Conclusion?Saline water irrigation deteriorates soil physical and chemical properties,reduces soil microbial biomass and basic respiration,changes the diversity of soil bacterial structure,and inhibits the absorption of water and nutrients by cotton,thus reducing cotton yield and water use efficiency.Biochar and straw application can improve soil structure,increase soil nutrients,promote soil basic respiration,and increase soil microbial biomass.At the same time,soil bacterial communities can adapt to salt stress by adjusting species composition,and ultimately promote cotton to absorb water and nutrients,and increase cotton yield and water use efficiency.