Analysis Of Supplemental Irrigation Threshold And Physiological Basis Of Efficient Water Use In High-yielding Wheat

The experiment was conducted xuanjiazhuang village,Tai'an,Shandong province from2015 to 2017 growing seasons using two high-yielding wheat varieties Shannong 29?SN29?and Shannong25?SN25?as test materials.SN29 set up two depths of soil moisture measuring,0-20 cm?D20?and 0-40cm?D40?,respectively,and one depth of soil moisture measuring?0-20cm?was set up for SN25.Three supplemental irrigation?SI?thresholds?Irrigation lower bounds?,70%FC?W1,FC represents field capacity?,60%FC?W2?and 50%FC?W3?were measured on the basis of consistent water management during seeding stage.The target relative soil water content after SI was 100%FC in soil depths of moisture measuring,no-irrigation after emergence?W0?and conventional border irrigation?W4?as the control treatment,meanwhile,experiment in sand cultures was studied to simulate soil environment before SI and process of rewatering,and study corresponding mechanism,the main results were as follows:1 Effect of the SI thresholds on the SI method and water consumption characteristics of wheatW3 treatment with SI at jointing and anthesis had lower SI amount and times than W1treatments during the whole growth period,high absorption rate of soil water in 100-200cm soil layer;The amount of SI and water consumption during the whole growth period of W1and W4 was relatively large,and the proportion of soil water consumption and precipitation in the growing season to total water consumption decreased.Soil water storage at 0-100cm soil layer of W3 treatment before SI at anthesis was lower than that of W1 treatment,soil water storage in 100-200cm soil layers was no significant difference between W3 and W1treatment,and significantly higher than W0 treatment.Under the condition of adequate soil moisture in sowing,SI at pre-wintering increased by 0-200cm soil water storage,but the total water consumption during before jointing increased,and the proportion of soil water consumption and total water consumption decreased in the growing season.It was not contribute to improving the water use efficiency of natural water supply.The above results showed that the relative soil moisture content in 0-20cm soil layer below 50%FC as SI threshold standard at the wintering,jointing and anthesis under the condition of adequate soil moisture,which could reduce SI times in wheat growing period and guarantee water supply at jointing and anthesis to achieve reasonable allocation of irrigation water during the whole wheat growing season.2 Effects of SI threshold on carbon assimilate and dry matter accumulation and distribution in wheatThe Leaf area index?LAI?in W3 treatment under D20 condition showed little difference with W1 treatment,which was lower than W4 treatment and higher than W0 treatment,and which ensured a certain photosynthetic area during the filling period.The LAI of every treatment under D40 condition of at the late filling stage was higher than that of corresponding threshold treatment under D20 condition,it showed that reducing the SI amount and times results in the decrease of photosynthetic area at the late filling stage.There was no significant difference in net photosynthetic rate?P_n?,stomatal conductance?Gs?,actual photo-chemical efficiency(?_PSII)and maximum photochemical efficiency?Fv/Fm?from 0 days after anthesis?DAA?to 20 DAA between W1 and W3 treatment,which were significantly higher than those of W0 treatment.W3 treatment was significantly lower than W1 treatment at 30 DAA,and the photosynthetic production capacity of flag leaf decreased.The SPAD value,P_n,Fv/Fm of SN25 after anthesis of flag leaf were higher than SN29,and the photosynthetic capacity was still maintained at the late filling stage,and the amount of assimilate input grain after anthesis decreased,which resulting in a decrease of economic coefficient?EC?.Pre-anthesis dry matter remobilization,Pre-anthesis dry matter remobilization efficiency and Contribution of pre-anthesis dry matter remobilization to grain in W3 treatment were higher than that of W1 treatment,while the contribution of post-anthesis dry matter accumulation to grain was lower than W1 treatment.Soluble sugar content of flag leaves in W3 treatment was higher than that of W1 treatment at 21 DAA,and was lower than that of W1 treatment and traditional barn irrigation at maturity.The results showed that 50%FC threshold treatment was conducive to promoting the transport of pre-anthesis dry matter remobilization and the redistribution of soluble assimilates from the vegetative organs to grain at the late filling stage,and increased the grain weight.3 Effect of SI threshold on nitrogen absorption,accumulation and assimilation in wheatWith the increase of drought degree before SI,the root absorption rate of NH₄⁺and NO₃^-in wheat seedling increased.The rhizosphere pH decreased under sufficient water supply and rewatering after drought,the absorption rate of NH₄⁺and NO₃^-by roots under 60%FC simulated drought was significantly higher than that of adequate irrigation.This showed that moderate drought increased the absorption rate of nitrogen ions in roots.Soil water content50-60%FC was conducive to forming a larger root/shoot ratio.Increasing nitrate reductase?NR?and Glutamine synthetase?GS?activity,elevating NH₄⁺-N content,reducing NO₃^--N content,and increasing amino acid content in root.Rewatering basised on soil water content50-60%FC did not affect the growth process of wheat,and the root morphological parameters,root activity,NR and GS activities in shoot had all strong water compensation effect,and amino acid content in root increased significantly.It indicated that the relative water content in wheat seedlings was above 60%FC without SI,and the metabolic capacity of wheat plants was enhanced with rewatering under 50-60%FC.SI at jointing and anthesis in W3 under the condition of D20,the decrease of root vigor after 10 DAA was lower than other treatments,but root vigor in W3 was lower than that of W1 treatment and W4 treatment after 30 DAA,which indicating that SI basis on 50%FC threshold was beneficial to maintain higher absorption capacity of root at mid-filling stage.W3 treatment promoted the translocation of nitrogen in vegetative organs into grain compared with other treatments under the conditions of same wetting soil layer,and increased the contribution of nitrogen in vegetative organs to grain and had higher nitrogen accumulation in grain.Moreover,the nitrogen transfer rate,grain nitrogen accumulation and its contribution rate to grain of flag leaf,stem,Spike axis&glume were all higher than those of W1 treatment.NR activity of flag leaf in mid-filling stage of W3 treatment was higher than that of W1 treatment,and was beneficial to transfer glutamic acid and proline in flag leaf to grain at late filling stage.Nitrogen transportation efficiency from leaves of SN25 was lower than that of SN29,but that of spike axis&glume was higher.4 Effect of SI threshold on Senescence characteristics of flag leafThe physiological activity of flag leaf after anthesis decreased with the decrease of SI threshold,and the physiological activity of flag leaf in dry-land variety was higher than that of irrigated-land variety.Compared with W1 treatment and W4 treatment,W3 treatment had no decrease in Superoxide dismutase?SOD?,Catahse?CAT?activity and soluble protein?SP?content at 10 DAA under the same wetting soil depth,but even had increased trend.The SOD,CAT activity of flag leaf in W3 decreased,malondialdehyde?MDA?content increased after30 DAA,and caused the decline of Photosynthesis and assimilation in flag leaf because of reducing the main natural water supply,which is beneficial to transportation of soluble assimilates in flag leaves and increasing grain weight.W1 and W4 treatment in D40 still maintained high physiological activity in flag leaves at late grain filling stage,which was not conducive to the transfer of soluble assimilates in flag leaves.SI basis on 50%FC threshold in0-20cm soil layer can maintain higher physiological activity and carbon assimilation ability of flag leaves in the mid-filling stage,the senescence of flag leaves accelerated and carbon assimilation ability decreased at late filling stage,but the root system still maintained a certain absorption capacity,the transfer of Assimilates in leaves was accelerated and the economic coefficient increased.5 Effect of supplementary irrigation thresholds on yield and water use efficiency of wheatIncreasing the main natural water supply before jointing stage could promote the occurrence of tillers in spring,reduce tiller survival rate,increase grains per spike,and decrease 1000-grain weight.W3 treatment decreased SI amount and times under same wetting soil layer,tiller survival rate,yield and WUE did not decrease,and IB increased significantly when compared with W1 and W4 treatment.W3 treatment in D20 decreased SI amount and the total water consumption of growth season compared with W3 treatment in D40,and there was no significant difference in yield,but water use efficency?WUE?and irrigation benefit?IB?all increased significantly,which of indicating that SI at jointing and anthesis basis on 50%FC threshold in 0-20cm soil layer reduced the water consumption during growing season and increased grain yield and WUE.WUE and IB of the traditional border irrigation were the lowest.Compared with the two varieties,the 1000-grain weight,grain yield,economic coefficient and IB of SN29 were significantly higher than those of SN25.Above all,soil moisture from 50%FC to 60%FC was beneficial to the root absorption of nitrogen ions,rewatering on this basis had a strong water compensation effect.Therefore,it is not necessary to SI above 60%FC at seedling stage.50%FC in 0-20cm soil layer as SI threshold at jointing and anthesis reduced SI amount,improved the utilization efficiency of soil water storage and natural precipitation,maintained higher carbon and nitrogen assimilation ability in the mid-filling stage,and facilitated temporary storage of carbon and nitrogen in vegetative organs to transfer and redistribution,resulting in increased grain weight,which of obtaining higher WUE and IB,this SI treatment?50%FC in 0-20cm soil layer?was the recommended treatment for farmers.