Yield Formation And Regulation Techniques With Stable Yield In Extremely-late Sowing Wheat Following Rice

Rice-wheat growing system is the main planting system in Jiangsu Province.Due to the expansion of simplified cultivation and the spreading of late-maturing rice varieties,rice harvest is delayed.In addition,it often rains during the wheat-sowing stage,hence wheat is sown later.The area of wheat sown in suitable date reduced greatly,and the area of late-sowing wheat increased to 119.36×104·hm-2,accounting for more than 49.7%of the wheat planting area in Jiangsu Province.Too late sowing has become a key factor restricting the improvement of wheat yield and grain quality.The contradiction is particularly prominent in Jiangsu.In order to further explore the effects of extremely late-sowing(30 days later than the optimum sowing date)on yield components,nitrogen absorption and utilization,and gain quality,the medium-gluten wheat Yangmai 25 was used as the material.Different populations were constructed through sowing date,seeding density and nitrogen fertilizer management,and the regulatory effects of management above on the yield composition,population formation,photosynthetic senescence physiology,nitrogen absorption and utilization as well as grain quality in extremely late-sowing wheat were studied.The suitable combination cultivation techniques of extremely late-sowing wheat Yangmai 25 were suggested,which provided a theoretical and technical support for getting stable yield,high grain quality and high efficiency in extremely late-sowing wheat after rice.The main results are as follows:1.The growth periods of extremely-late sowing wheat following rice were correspondingly postponed compared with the suitable sowing wheat.The radiation use efficiency of extremely-late sowing wheat was lower than that of suitable sowing wheat before booting,and higher than that of suitable sowing wheat after booting.The radiation use efficiency of the whole growth duration dropped by 17.8%.The heat utilization efficiency was lower than that of suitable sowing wheat before jointing and higher than that of suitable sowing wheat after jointing.The heat utilization efficiency of the whole growth period dropped by 7.5%.2.Population quality indexes of high and stable yield more than 8000 kg·hm-2 under the condition of extremely-late sowing were clarified.The number of ears,grains per ear and thousand-grain weight of the population were 540×104·hm-2-590×104·hm-2、32-37 and 41 g.The main characteristics of the population formation was as follows:the number of stems and tillers at tillering stage was about 1.3 times of the final ear number.The highest number of tillers and stem at the jointing stage was more than 1300×104·hm-2,which was about 2.3 times of the final ear number,and the ear percentage of stem and tillers was higher than 43%.The dry matter accumulation at maturity reached more than 21000 kg·hm-2.The dry matter accumulation after flowering was more than 7000 kg·hm-2 and that to the grain yield ratio increased to over 88%.The leaf area index at the booting stage was higher than 7.0,and the LAI at the milking stage was about 3.6.3.Difference in nitrogen absorption and utilization between extremely-late and suitable sowing wheat was found.Compared with suitable sowing wheat,the nitrogen accumulation in each growth period of extremely-late sowing wheat decreased.When the seeding density increased to 375×104·hm-2,the nitrogen accumulation at each of growth stage and nitrogen absorption increased from seeding to tillering,tillering to jointing,and flowering to maturity.The activities of GS enzyme and GOGAT enzyme in flag leaves after anthesis also advanced.Compared with suitable sowing and low-density treatment,although the nitrogen uptake at each stage reduced under the late sowing and high-density treatment,the nitrogen uptake rate after anthesis significantly increased.Therefore,the nitrogen absorption and utilization capacity of extremely-late sowing wheat with the density of 375×104·hm-2 significantly improved,and the apparent nitrogen utilization maintained around at a rate of 40%.4.The SOD,POD and CAT enzyme activities in the flag leaves after anthesis significantly improved under the treatment of seeding on December 1,planting density 375×104·hm-2,nitrogen application 225 kg·hm-2,nitrogen applied ratios of basis:tillering:jointing:booting 4:2:0:4.Hence,the SPAD value and net photosynthetic rate of the flag leaf maintained at a high level,which was beneficial to delaying leaf senescence after anthesis.The grain filling rate kept at a high level of 1.99-2.07 mg·d-1·grain-1 from 15 DAA(days after anthesis)to 28 DAA and the grain weight increased in the end,which was beneficial to achieve stable or high wheat production.5.Cultivation regulation techniques of extremely-late sowing wheat following rice with grain yield more than 8000 kg·hm-2 and good grain quality were suggested.The combination of high-yield and high-quality cultivation techniques for the extremely-late sowing wheat Yangmai 25 was as follows:sowing on December 1,planting density of 375×104·hm-2,the applied amount of N,P2O5,K2O 225 kg·hm-2,90 kg·hm-2 and 90 kg·hm-2,respectively,nitrogen fertilizer ratios of basis:tillering:jointing:booting 4:2:0:4.The grain processing quality,nutritional quality and dough rheological characteristics could meet the national standard for medium-gluten wheat,and the nitrogen fertilizer utilization rate also improved.The net income was more than 8,000 yuan·hm-2.Auxiliary measures such as seed soaking and mulching at the early growth stage,and spraying of growth regulators at the late stage of growth had good effects on the germination of seeds,the occurrence of tiller,and delaying leaf senescence after flowering,as well as significantly improving yield of extremely-late sowing wheat.