Physiological Basis For Regulation Of Supplemental Irrigation At Jointing Stage On Yield And Water Use Efficiency Of Winter Wheat With Different Sowing Schemes

The jointing to flowering stages is the key period of spike formation and grains setting,and the water management in this stage significantly affects grain yield.Winter wheat with different sowing date and planting density creates different population structure.In order to reveal the effect of supplemental irrigation at jointing on grain yield,water use efficiency and the physiological characteristics of winter wheat with different sowing date and planting density,two years experiment（2018-2020）was conducted at Xuanjiazhuang village,Daolang Town,Daiyue district,Tai’an City,Shandong Province（36.12°N,116.55°E）.A split-split-block design was used in the experiment.The main plot was wheat cultivars（large-spike cultivar,cv.Shannong 23 and multi-spike cultivar,cv.Shannong 29）with different spike–type.The sub plot was the sowing scheme（sowing date×planting density）,setting up suitable sowing dates and seeding rate（A1）,and delayed in sowing date and increased planting density（A2）.Setting up 120.0×10⁴ plants·hm^-2 for sowing on October 5（A1）,and 240.0×10⁴ plants·hm^-2 for sowing on October 12（A2）were set from 2018 to 2019.And setting up 187.5×10⁴ plants·hm^-2for sowing on October 5（A1）,and 375.0×10⁴ plants·hm^-2for sowing on October 12（A2）were set from 2019 to 2020.The deputy plot was the supplemental irrigation（SI）scheme,three levels were set up:no irrigation at the jointing stage（W0）,SI at zero days after jointing stage（W1）,and SI at 14 days after jointing stage（W2）.Both W1 and W2 treatments made the soil relative water content of 0–20 cm（plan wetting layers）reach 100%field water holding capacity.The formula I=10×γ×H×（FC-β_j）was used to calculate the required supplemental irrigation amount.Whether the supplemental irrigation was needed at the sowing,wintering and flowering stages determined by the on-demand supplemental irrigation system.The main results are as follows:1 Effects of SI on water consumption characteristics of winter wheat with different sowing schemesUnder A1 condition,W1 and W2 treatments had no significant differences on the total water consumption.Under A2 condition,compared with W1 treatment,W2 treatment significantly increased the consumption of soil water,reduced the use of supplemental irrigation,and significantly increased the total water consumption.2 Effects of SI on carbohydrate content of tillers in winter wheat with different sowing schemesThe sucrose and soluble sugars content reduced after irrigation at jointing under A1condition,however,the contents remained high levels in the treatment with W2 than W1.Under A2 condition,whatever supplemental irrigation,the sucrose and soluble sugars content of T1（tiller growing from the axils of the first true leaf of the main stem）was significantly greater than that in T4（tiller growing from the axils of the 4th true leaf of the main stem）,which increased the difference of carbohydrate between tillers and lead to the decrease of the spike formation of tillers.3 Effects of SI on antioxidant characteristics of tiller leaves in winter wheat with different sowing schemesUnder A1 condition,W1 and W2 treatments could significantly reduce the MDA content of T1 and T4,increase the SOD activity and soluble protein content.Under A2 condition,SI at jointing stage could increase the SOD activity and soluble protein content of T1 and decrease the MDA content,W1 treatment could decrease the SOD and CAT activity and MDA content of T4,while W2 treatment could increase the SOD activity and decrease the soluble protein content of T4,but had no significant effect on MDA content.Under the same sowing scheme,compared with W1 treatment,W2 treatment maintained the activities of SOD and CAT and the content of soluble protein in T1 leaves at a higher level,and delayed the senescence process of T1,while the antioxidant enzyme activities of T4 had little difference between W1 and W2treatments.4 Effects of SI on endogenous hormone content of tiller leaves in winter wheat with different sowing schemesUnder the same sowing scheme,the SA contents of T1 and T4 in W1 treatment were significantly increased,but the high levels ABA and JA content of T4 limited its survival and spike formation.Although W2 could reduce the hormones of T1 and T4,the ABA content of T4 was significantly higher than that of T1.5 Effects of SI on spike formation of winter wheat with different sowing schemesUnder A1 condition,the population structure was mainly tiller spike,and W1 treatment can significantly improve the percentage of earbearing tiller,percentage of available tiller and number of panicles per plant of SN23,significantly reduce the percentage of spikes on main stem,and increase the ear number.Under A2 condition,the population structure was that the main stem and tiller were equally important.Different irrigation schemes at jointing stage had no significant effect on the percentage of earbearing tiller,percentage of available tiller,number of panicles per plant,percentage of spikes on main stem of the two varieties.Under the same sowing scheme,compared with T4,the content of ABA,JA and SA in T1 was lower,and the content of soluble protein was significantly increased under W1 treatment,which delayed tiller senescence and improved percentage of available tiller.Under W2 treatment,compared with T1,the content of ABA and MDA in T4 was higher than T1,and SOD and CAT activity,SA and soluble protein content were low,which made T4 die out.6 Effects of SI on grain yield and water use efficiency of winter wheat with different sowing schemesCompared with W1 treatment,W2 treatment reduced the spike number,but the significant increased of grain numbers per spike and 1000-grain weight resulted in the higher grain yield.Under A1 condition,W2 treatment increased water use efficiency and irrigation efficiency,however,the water use efficiency was decreased and the water productive efficiency was increased under A2 condition.In summary,whatever the conditions of suitable sowing dates and seeding rate or delayed in sowing date and increased planting density,delayed the irrigation time to 14 d after jointing,T4 of Shannong 23 and Shannong 29 had higher content of ABA and MDA,lower activity of SOD and CAT,and lower content of SA and soluble protein,which accelerated the extinction of T4 and reduced the percentage of available tiller.But delayed the irrigation time to 14 d after jointing significantly increased the grain numbers per spike,1000-grain weight,grain yield and water productive efficiency.Under the condition of suitable sowing dates and seeding rate,the population structure was mainly tiller spike,supplemental irrigation 14 days after jointing could significantly improve water use efficiency because supplemental irrigation had no effect on total water consumption.Under the condition of delayed in sowing date and increased planting density,the population structure was that the main stem and tiller were equally important,irrigation 14 days after jointing significantly increased the water consumption from jointing stage to flowering stage,which significantly increased the total water consumption,so the water use efficiency decreased.