Study On Effect Of Irrigation And Fertilization Regulation And Simulation Of Cotton Growth Under Film-mulched Drip Irrigation In Southern Xinjiang

The shortage of water resources and soil salinization are the main problems of cotton planting in Xinjiang.Film-mulched drip irrigation has been applied in Xinjiang for nearly25 years for its advantages of increasing soil temperature,preserving soil moisture and reducing soil salinization.Study on the mechanism of water-fertilizer regulation is helpful to optimize and promote the application of film-mulched drip irrigation in saline alkali soil.In this paper,cotton?Gossypium hirsutun L.?was used as the research object,and field experiments were carried out in the key irrigation experimental station of the Ministry of water resources of Xinjiang Institute of water resources and Hydropower Science in Sinal Town,Bayingolin Mongolian Autonomous Prefecture,Xinjiang Uygur Autonomous Region from 2015 to 2016.The irrigation system is based on local cotton water demand and conventional irrigation amount of 500mm.Different irrigation treatments T1-T8 were set,in which T6 was fully irrigated in 2015,and the remaining treatments were set proportionally according to T6?t1-t5?;in 2016,only two irrigation treatments were set,full irrigation T7 and deficit irrigation T8.In the two growth stages,the fertilizer was fully applied according to the recommended amount of fertilizer by local farmers.From April to October of 2018-2019,another experiment was carried out at the 31st Regiment of the Second Agricultural Division,which belongs to the Tarim Reclamation Area of the Second Agricultural Division of Xinjiang Production and Construction Corps.Two factors?water regulation and fertilizer amount?were set during the 2018 and 2019 cotton growing seasons.Based on the reference evapotranspiration,0.4?0.6 and 0.8 times of reference evapotranspiration?i.e.0.4 ET₀?0.6 ET₀ and0.8 ET₀?were established as W1-W6 in the cotton budding and flowering stages,and a full irrigation treatment ET₀,namely CK;The fertilization rates were 450-157.5-67.5 N-P₂O₅-K₂O?F1??360-126-54 N-P₂O₅-K₂O?F2??300-105-45 N-P₂O₅-K₂O?F3??240-84-36 N-P₂O₅-K₂O?F4??150-52.5-22.5 N-P₂O₅-K₂O?F5?and 0-0-0 N-P₂O₅-K₂O?F0??i.e.1.5F?1.2F?F?0.8F?0.5F and 0F?.Another treatment namely LD for bare land was added.There were 13 treatments in total.The laws of water saving and yield increasing and water-salt movement were revealed,and the corresponding control strategies were put forward.Meanwhile,considering the effects of film mulching and water stress,the DSSAT model could not be simulated by using the experimental data from 2015 to 2016 The crop growth under the condition of membrane was improved,and the model was improved according to the experimental data from 2018 to 2019,and the genetic coefficients in line with the research area and cotton varieties were screened out,and the cotton growth and development process in the experimental year was simulated.The main conclusions are as follows:?1?The effects of different irrigation-fertilizer regulation on cotton growth,yield,quality and water and fertilizer use efficiency were revealed.The higher value of plant height among different water treatments appeared in deficit irrigation treatment?W4,W5 and W6?at flowering and boll stage,with an average of 72.92cm,which was 36.63%and 3.03%higher than that of deficit irrigation treatment?W1,W2and W3?and CK,respectively.The water use efficiency?WUE?of W6 was the highest(1.63 kgm^-3 and 1.52 kgm^-3,respectively).The average aboveground biomass of F1treatment was 25880.75kg/ha,which was 41.66%,40.6%,46%,14.19%and 4.12%higher than that of F0,F5,F4 and F2,respectively.The relationship between yield and fertilizer amount was in line with quadratic parabola,and the critical point was 1.2 times of fertilizer amount.The effects of different control methods on fertilizer partial productivity,seed cotton yield and water use efficiency of cotton field were extremely significant?P<0.01?,and the single boll weight was significantly affected?P<0.05?.During the two growth stages,except CK,F1 and F2 treatments,the micronaire value was at the level of B,and the other treatments were lower than grade C?standard grade?,The fiber length is also in the standard level and above,and the breaking strength is directly proportional to the total amount of irrigation and fertilization.?2?Soil water movement and water consumption in cotton field under different irrigation control measures were explored.During the growth period of cotton,soil moisture was greatly affected by soil surface evaporation,root water absorption and groundwater activities.The surface soil moisture showed different changing patterns:narrow row>wide row>bare land,20-40cm showed bare land>wide row>narrow row,and the deep soil moisture gradually tended to be stable and uniform.By calculating the water consumption of cotton,it is concluded that there are deep seepage and groundwater recharge in this area,The total water consumption?CK?of cotton in the whole growth period of 2018 and 2019 were 506.96 and 509.52,respectively.Compared with bare land treatment,crop water consumption was reduced by43.6 mm and 53.5 mm respectively,but there was no significant difference?P>0.05?.Compared with the bare land treatment,the control treatment significantly reduced the soil evaporation between trees by 41.44 and 41.81%?corresponding amounts were 163.16 and161.5 mm?,and increased plant transpiration t by 43.4 and 37.93%?corresponding amounts were 119.56 and 108 mm?.The cumulative reference evapotranspiration ET₀ was 978.33mm and 955.99 mm,and the average daily reference evapotranspiration intensity was 6.2mm/d and 6.1 mm/d,respectively.?3?The law of soil salt movement and the evolution of Na⁺,Cl^-ions in cotton field under different irrigation-fertilizer regulation measures were studied.The spatial distribution characteristics of soil salt movement were narrow row>wide row>bare land,in vertical direction,with the increase of soil depth,it first increased and then decreased.There were significant differences in salt content among different water treatments?P<0.05?,according to the degree of deficit,the salt accumulation was as follows:severe>moderate>mild,and the minimum salt accumulation occurred in the flowering and boll stage;there were also significant differences in salt content among different fertilization treatments?P<0.05?,and the soil salt content increased with the decrease of fertilizer application,and the salt accumulation in F0 without fertilization was the highest,reaching 3400 and 4094 g/m²,respectively.The lowest salt accumulation occurred in the F2 treatment with 1.2 times of fertilizer application,reaching 1574 and1976 g/m²,which was 25.7%and 24.9%lower than that of F3.The changes of soil Na⁺and Cl^-in horizontal and vertical directions were basically consistent with soil salt content.The decreasing rate of Cl^-was W6>W5>W3>W2>W4>CK>W1>LD;the increasing rate of Na⁺from high to low was:LD>W1>W2>W3>W4>CK>W5>W6.?4?The parameters of cotton varieties suitable for the region were put forward,and the growth and development model of cotton under film-mulched drip irrigation with deficit irrigation was constructed.Based on the CSM-CROPGRO-COTTON cotton growth module of DSSAT model,the calculation of potential evapotranspiration,soil surface evaporation and water stress factors were improved according to the actual production and planting situation of cotton.The simulation of leaf area index,aboveground dry matter,yield,phenological period and soil moisture of cotton were verified by many years of experimental data.The results show that the improved model can better simulate the cotton growth and development process under different water stress under film-mulched drip irrigation,and it is a reasonable decision-making system for sustainable agricultural irrigation management.At the same time,it can also provide research means for predicting cotton yield and growth under the changes of water and fertilizer environment,meteorology and soil environment in the future.