| The Alxa League in the west of Inner Mongolia has a vast land area,rich light and heat resources,suitable for cotton growth,and is plans to use as a national reserve cotton area.However,there is little precipitation,a lot of wind and sand,strong evapotranspiration in farmland,shortage of water resources and inefficient use of crop water,which are the main problems that restrict cotton production in this area.Exploring the effective way of water supply in cotton fields and clarifying the relationship mechanism between cotton field water consumption and cotton production is a scientific problem that needs to be solved to achieve efficient water use and expand agricultural land resources,and it is also a theoretical basis for supporting applicable technological innovation.In this study,the cotton variety 'China Cotton Institute 92' was used as the test material.In 2016-2018,Ejina Banner,Alxa League,western Inner Mongolia.the cotton experimental demonstration base of the Inner Mongolia Academy of Agriculture and Animal Husbandry Sciences,set up two irrigation methods:drip irrigation under film and trace irrigation In the field test of locating cracked areas.In the experiment,drip irrigation under the film,the irrigation volume of 360 mm was used as the control(CK),and the trace irrigation settings were T1,T2,T3,T4,T5(the buried depth was 30 cm,and the irrigation volume was 360,330,300,270 and 240 mm,respectively)),T6,T7,T8,T9,T10(buried depth 40 cm,water volume the same as above),T11,T12,T13,T14,T15(buried depth 50 cm,water volume the same as above),etc.16 treatments.Through analysis and comparison of the temporal and spatial dynamics of soil moisture between different treatments,the effect of cotton field water supply on water consumption,cotton root biomass accumulation and physiological response,above-ground morphology,photosynthetic characteristics,leaf transcriptome profile expression,and cotton yield,quality,and water use effects,Reveal the influence mechanism of trace irrigation on cotton field water supply and cotton growth,and provide theoretical basis and technical support for the technical innovation of high-efficiency utilization of cotton field water using trace irrigation.The main results are as follows:1.The soil water supply of trace irrigation is vertically distributed in the shape of"inverted pine cones",which has the characteristics of restraining soil evaporation and effective water supply of the soil.Compared with drip irrigation,the soil moisture content of the soil layer of 10-20 cm under the buried depth of the trace irrigation pipe network has the maximum.In the budding stage when cotton consumes less water,on average for two years,the water content of the surface soil at the depth of 0-10 cm for each trace irrigation pipe network is only 25.86%to 70.68%of that of drip irrigation(CK).The soil moisture content of the deep-treated 20-40 cm soil layer is 67.9%?104.15%of that of drip irrigation(CK).Compared with drip irrigation under mulch(CK),trace irrigation significantly reduces the soil moisture content of the topsoil layer,which is beneficial to curb the direct evaporation of soil water;the corresponding higher soil moisture content of the 20-40 cm soil layer is beneficial to direct crop roots.Water supply.The results show that if the pipe network is buried too deep,the root water absorption will be limited and the soil moisture content will increase.2.The cotton root biomass grows in a "double S" curve,and the 0-40 cm soil layer has the largest root surface area and root length density.In irrigated fields in the arid area of Mengxi,the cotton root biomass during the budding stage increased rapidly,and the root weight growth accounted for 40.5%of the entire growth period;the root biomass increased slowly during the blooming and boll stage,and the root weight growth during the period accounted for 5.6%of the growth period;The root biomass increased rapidly during the boll opening and the weight gain accounted for 32.8%of the growth period.In the cotton field,the root surface area density of 0-40 cm is 1.401-1.487 times that of the 40-80 cm soil layer,and the root length density is 1.383-1.772 times that of the 40-80 cm soil layer.The spatial agreement between root length density of T1 treatment and soil moisture in blooming and boll stage was 93.9%,which was 28.8%higher than that of drip irrigation(CK);root weight of T1 treatment was 20.73%higher than that of CK,root surface area density,root length Compared with CK,the density and root volume density increased by 15.13%,40.36%,30.48%,and the root vigor increased by 43.59%.3.The growth rate of cotton biomass was in a "bell" shape,and the water supply rate of cotton field was in a "down cymbal" curve,and the water supply in the seedling stage was in poor agreement.The cotton field water consumption under trace irrigation is significantly related to the irrigation water volume and the buried depth of the pipe network in quadratic terms,and the water consumption decreases with the decrease of the irrigation water volume and the increase of the buried depth of the pipe network.Water consumption in cotton fields is mainly concentrated in the blooming and boll stage and the budding stage,followed by the boll opening stage and the seedling stage.In the two years,the water consumption of cotton field during the growth period was the lowest in T15 treatment,and the water consumption of T1,T6 and CK was the highest.Quantitative estimation of the crown-water coincidence degree of the above-ground biomass growth rate of the cotton under the 1360 background and the cotton field water supply rate.The crown-water coincidence degree of the growth period of the drip irrigation(CK)under mulch in 2016 is about 70.5%,and the corresponding T1 is 78.8%,T6 is 71.4%,T11 is 59.2%;T15 is 35.9%.In 2017,the crown-water anastomosis during the growth period CK was 73.1%,T1 was 61.6%,T6 was 70.2%,T11 was 61.9%,and T15 was 39.9%.The results showed that the rate of water supply in the cotton field at the seedling stage was inconsistent with the growth rate of the above-ground and root biomass of plants,which reduced the water use efficiency during the period.The budding stage and the bloomingr-boll stage are the periods of rapid plant growth.Irrigation and water supply become the key to water consumption during the growth period.4.The decrease in irrigation volume and the deepening of the water supply layer reduce the leaf chlorophyll content and net photosynthetic rate,which affects the transcriptome expression.The chlorophyll content of cotton leaves showed a decreasing trend with the decrease of irrigation amount;the chlorophyll content of each irrigation amount treatment under the mark irrigation depth D30 was higher than the corresponding treatments under D40 and D50 at each growth stage of cotton.The daily changes of net photosynthetic rate and stomatal conductance of cotton under different treatments showed a bimodal curve trend;the net photosynthetic rate and stomatal conductance of each irrigation treatment under trace irrigation D30 were higher than those under the corresponding D40 and D50 treatments.Illumina transcriptome sequencing showed that 4555 non-overlapping differentially expressed genes(DEG)were identified in cotton plants treated with drip irrigation under the membrane(CK)as a control and buried deep in the scar irrigation pipe network.Through comparative analysis,4726 non-overlapping DEGs were identified.The DEG identified from the D30(2008)and D50(4050)treatments exceeds that of the D40(107)treatment,and the distribution of DEG changes relatively drastically.These DEGs are related to the tolerance of plants to abiotic stress and drought.Therefore,different irrigation methods affect the growth of cotton by regulating the expression of the transcriptome profile.5.Cotton production increased in a nearly linear positive correlation with the increase in effective water supply and water consumption,and WUE also increased in a positive correlation.The output of cotton seed cotton and lint increases with the increase of irrigation water,and decreases with the increase of buried depth of the pipe network at higher irrigation water.The relationship between 2016 irrigation quota(x1),buried depth of pipe network(x2)and cotton seed cotton yield(y)is:y2016=-9421.17+78.44x1+47.97x2-0.254x1x2-0.094x12+0.583x22(R2=0.651)?The seed cotton yields of T1 and T11 treatments under trace irrigation were the highest,which were 6601.5 and 6574.5 kg/hm2,respectively,which were 0.78%and 0.37%higher than that of drip irrigation(CK).In 2017:y2017=-12189.79+86.55x1+30.97x2-0.168x1x2-0.103x12+0.178x22(R2=0.938)?Drip irrigation under mulch(CK)had the highest yield of seed cotton,5557.20 kg/hm2,and T1 of mark irrigation was 5247.15 kg/hm2,which was not significantly different from drip irrigation under mulch.The yield of cotton seed cotton increased with the increase of effective water supply(R2=0.4983?0.9690)and water consumption(R2=0.5481?0.9729),and the water use efficiency increased in a positive correlation with the increase of cotton seed cotton production(R2=0.5077?0.9295).In summary,trace irrigation creates an "inverted pine-cone" water supply structure under the soil,which improves the empty sequence and timing coincidence of cotton field water supply and cotton water demand;The topsoil mulch with low moisture content effectively curbed soil water evaporation and improved water use efficiency.Trace irrigation can obtain cotton yield and quality close to those of drip irrigation under mulch.Studies have shown that water supply is a decisive factor for the high yield of cotton in the arid area of West Inner Mongolia.There is still potential for further improving farmland water supply technology and increasing water use efficiency. |
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