| Cotton was a main cash crop in Xinjiang.It was a very key task for developing agricultural economy to improving cotton yield in Xinjiang.However,soil salinization and water shortage were two main factors resulting in soil degradation and decreasing cotton yield in Xinjiang.Biochar could be not only a very potential soil amendment,but also promot crop growth and increase crop yields.Sugar beet was a moderately salt-tolerant crop,which could be used as a biological salt reduction measure.This was mainly due to the fact that sugar beets could absorb salt ions in saline soil,and further reducing soil salt.In this study,biochar amendment and sugar beet planting were closely combined to explore the effect of biochar application and sugar beet planting on improvement of saline soil and increase of crop yield under film-mulched drip irrigation.It was of great significance for Xinjiang oasis to achieve high-efficiency agricultural water use and the sustainable development of saline soil.Therefore,a three-year field experiment was conducted in a cotton field located in the second company of the 31st regiment(86°56?58?E,40°53?03?N),Yuli County,Bayingolin Mongol Autonomous Prefecture of Xinjiang Uygur Autonomous Region between 2018 and2020.This experiment contained six biochar application rates,which were 0(CK),10(B10),25 t hm-2(B25),30 t hm-2(B30),50 t hm-2(B50),and 100 t hm-2(B100),respectively.Biochar application,film-mulched drip irrigation technology,and sugar beet planting were combined to explore effect of biochar application rates on soil properties and growth of cotton and sugar beet.This study explored regulation mechanism of biochar on physical and chemical properties of saline soil,and revealed the mechanism of biochar on growth of cotton and sugar beet.This study proposed a synergistic salt reduction technology mode for biochar application and sugar beet planting.This study determined a suitable biochar application amount for improving saline soil and promoting growth of cotton and sugar beet.This study objectively and systematically evaluated the suitable biochar application amount for cotton and sugar beet production through the entropy weighted DTOPSIS method and principal component analysis method.It is hoped that this research could provide theoretical support for sustainable agricultural development in Xinjiang.(1)This study clearly analyzed the influence mechanism of biochar application on bulk density,soil porosity,soil temperature,soil evaporation and hydraulic parameters.Biochar application could effectively reduce bulk density and increase soil porosity in 0-30 cm soil layer under film-mulched drip irrigation.Biochar application could improve soil temperature in 0-25 cm soil layer,and increase soil evaporation in the bare soil area.Soil temperature and cumulative evaporation volume could increase with increasing biochar application amount.Biochar application could also increase soil water storage,field capacity,permanent wilting point,saturated water content,and plant available water,but these indicators first increased and then decreased with increasing biochar application amount.A four-parameter Gaussian equation was used to analyzed relationships between biochar application rate and field capacity,permanent wilting point,saturated water content,plant available water,and planar soil water storage.We recommended that biochar application amount of 10-25 t hm-2 could be effectively used to improve hydraulic properties of the saline soil.(2)This study clarified the influence mechanism of biochar application on soil salinity,sodium ions,potassium ions,nitrate nitrogen,ammonia nitrogen,available phosphorus,and available potassium under film-mulched drip irrigation.Biochar application could affect the distribution of soil salt,sodium ions,and potassium ions in the 0-40 cm soil layer,and increase planar soil salt storage,salt accumulation,sodium ions and potassium ions.In addition,biochar application could also increase nitrate nitrogen,ammonia nitrogen,available phosphorus,available potassium and organic matter contents.Soil salt storage,salt accumulation,sodium ions,potassium ions,nitrate nitrogen,ammonia nitrogen,available phosphorus,available potassium,and organic matter content gradually increased with increasing biochar application amount,and the maximum appeared in the biochar treatment of 100 t hm-2.(3)This study revealed the influence mechanism of biochar on cotton growth indicators,yield composition,nutrient absorption,yield-increasing effect,and water-fertilizer productivity.Biochar application could effectively promote cotton plant height,stem diameter,leaf area index,taproot length,taproot dry matter,above-ground dry matter,chlorophyll content,cotton yield composition,nutrients(nitrogen,phosphorus and potassium)uptake of root,stem,and leaf.Biochar application could also increase cotton yield,irrigation water productivity,partial fertilizer productivity,and economic benefits,but it had no significant effect on fiber quality of cotton.Cotton growth indicators,yield composition,cotton yield,irrigation water productivity,partial fertilizer productivity,and economic benefits all showed a“unimodal curve”that first increased and then decreased with increasing biochar application amount.This study used a four-parameter Gaussian equation to analyze relationships between biochar application rates and cotton yield,irrigation water productivity,and partial fertilizer productivity.Cotton yield and irrigation water productivity in the biochar treatment of 10 t hm-2 were the largest Among all the biochar treatments,which were 4784-7417 kg hm-2 and 2.61-2.85 kg m3 t hm-2,respectively.Compared with the CK,the water and fertilizer productivity of B10 treatment increased by 19.4%-45.5%.(4)The study clarified the influence mechanism of biochar on sugar beet growth indicators,nutrient absorption,yield increase effect and water and fertilizer productivity,quantified the synergistic improvement of salt reduction by biochar and sugar beet,and proposed a synergistic salt reduction technology combining biochar application with sugar beet planting mode.Biochar application significantly increased plant height,tuber diameter,tuber length,leaf area index,aboveground dry matter,tuber dry matter,and nutrient(nitrogen,phosphorus,and potassium)uptake of sugar beet stems and tubers under film-mulched drip irrigation.Biochar application could also increase sugar content of beet tubers,sugar beet yield,irrigation water productivity,and partial fertilizer productivity.The growth index of sugar beet,nutrient uptake and salt uptake of sugar beet branches and tubers,sugar beet yield,irrigation water productivity,and partial fertilizer productivity all showed a single peak curve that first increased and then decreased with increasing biochar application amount.Biochar treatment of 10 t hm-2 had the highest sugar beet yield and irrigation water productivity,which were 99.3-123 t hm-2 and 0.38-0.62 kg t hm-2 mm-1,respectively.Compared with the CK,the biochar treatment of 10 t hm-2 increased water and fertilizer productivity of sugar beet by 29.5%-39.6%.Biochar application and sugar beet planting synergistically enhanced salt uptake of sugar beet branches and roots,and biochar treatment of 10 t hm-2 achieved the largest salt uptake(806.2-1022.9 kg hm-2 and 777.6-1264.9 kg hm-2)in above-ground branches and underground tubers of sugar beet.Compared with the CK,the biochar treatment of 10 t hm-2 increased salt uptake of above-ground branches and underground tubers by 43.1%-134.8%and 93.3%-207.7%,respectively.(5)The analysis results of entropy weighted DTOPSIS method and principal component analysis method showed that the biochar treatment of 100 t hm-2 had the worst effect on cotton and sugar beet,but biochar treatment of 10 t hm-2 had the best effect on cotton and sugar beet.Therefore,biochar application rate of 10 t hm-2 was suitable for cotton and sugar beet production,and biochar application rate of 10 t hm-2 and sugar beet planting could have a better salt reduction effect. |
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