Optimal Double-delay In Winter Wheat-summer Maize Double Cropping System In North China Plain And Its Efficient Regulation Of Water And Fertilizer

In order to improve annual water(rainfall and irrigation)use efficiency,we investgated the optimal rotation time of summer maize and winter wheat through delay tradition rotation time of winter wheat and summer maize production system in North China Plain(NCP).In addition,we also investgated a way to constructe high-yield and-efficiency crop community by agronomic management practices(irrigation,fertilizer,planting density and chemical regulation).The purpose of this research was to provide theoretical and practical basis for sustainable high-yield and-efficient production in NCP.The main results were as follows:1 The effect of double-delay on annual grain yield and water use efficiencyAccording to farmers' practice(FP,summer maize harvested on 9/25 and winter wheat sown on 10/1),we employed three treatments that each delayed both the maize harvesting and wheat sowing for 10 days(DHS-10),20 days(DHS-20),and 30 days(DHS-30).We examined the effects of these strategies on annual yield and water use by conducting a 2-year field experiment at Wuqiao Experiment Station in NCP.No significant differences were observed in annual grain yield among the FP,DHS-10,and DHS-20 treatments,while the results for these treatments were significantly higher than those in DHS-30 treatment.For all of the treatments,the grain yield of winter wheat decreased with the delay of sowing and the grain yield of summer maize increased with the delay of harvesting.For annual rotation,improved grain yield in maize season compensated for reduced yield in wheat season,for both DHS-10 and DHS-20 treatments compared with FP.Total water consumption(WC)followed as FP>DHS-10>DHS-20>DHS-30.WC in DHS-10 and DHS-20 decreased by 5.6%and 10.7%,respectively,compared with FP.Higher net economic benefits compared to FP(NEB)was also obtained in DHS-10(+ 495.4? ha-1)and DHS-20(+ 877.0 ? ha-1).2 The effect of limited-irrigation on root and canopy growth of witer wheat and its water use efficiencyThe three irrigation regimes used were no-irrigation(no water applied after sowing),limited-irrigation(60 mm of water applied at elongation),and sufficient-irrigation(a total of 180 mm of water applied,with 60 mm at regreening,elongation,and anthesis stages,respectively).Soil water storage,soil reservoir capacity,root length density,leaf expansion,water use efficiency(WUE),and grain yield of winter wheat were measured.The highest WUE was observed in the limited-irrigation treatment,achieving a relatively high grain yield.With increases in water(i.e.,sufficient-irrigation),winter wheat grain yield increased,but water WUE decreased.Limited-irrigation hampered leaf expansion,which can reduce transpiration,and slightly reduced grain yield compared to the sufficient-irrigation treatment.Moreover,limited-irrigation stimulated roots to grow into deeper soil layers and thus enhanced the uptake of soil-stored water from the subsoil layer,developing a large soil reservoir capacity to store rain-water in summer.3 The effect of planting density and nitrogen applying rate on nitrogen utilization and grain yieldField experiments were conducted in 2014 and 2015,using two planting densities(67,500 plants ha-1 and 90,000 plants ha-1)and three rates of N application(0 kg N ha-1 180 kg N ha-1-the recommended N rate and 360 kg N ha-1-the traditional N rate)in Wuqiao County in NCP.The grain yield(GY),N use efficiency(NUE),agronomic N efficiency(AEN)and N partial productivity(PFPN)in 90,000 plants ha-1 treatment were significantly increased by 6.6,3.9,24.7 and 8.8%than those in 67,500 plants ha-1 treatment,while the N2O emission intensity and greenhouse gas intensity were dereased by 7.3 and 4.3%;the NUE,AEN and PFPN were significantly increased by 6.2,96.0 and 98.7%without GY loss when the N applying rate reducing from 360 kg N ha-1 to 180 kg N ha-1,while the N2O emission intensity and greenhouse gas intensity in N180 were dereased by 65.1 and 85.0%than those in N360.In the present study,optimization of increasing planting density(90,000 plants ha-1)and reducing N rate(180 kg N ha-1)resulted in higher N utilization(NUE,AEN and PFPN)GY with lower environmental cost in maize production.The increase in N utilization and high GY of summer maize in 90,000 plants ha-1 with 180 kg N ha-1 treatment were essentially duo to the increased N-uptake capacity and N-transfer capacity.4 The effect of ED AH on stalk quality and canopy of summer maize at high densitiesWe conducted experiments during the 2014 and 2015 growing seasons.Hybrid maize cultivars'Xundan20'(lodging-susceptible)and 'Zhengdan958'(lodging-resistant),which are widely planted in China,were grown at a density of 90,000 plants ha-1.ED AH solution at a concentration of 2 mL L-1 was sprayed onto summer maize foliar surfaces at the seven-expanded-leaves stage.Grain yield,stalk quality(rind penetration strength,dry weight per cm,amount and area of vascular bundles,and bleeding sap)and leaf area were determined.ED AH significantly decreased lodging rate(by 60.1%on average),plant height,ear height and the location of the center of gravity in both varieties over two years,and increased rind penetration strength,dry weight per cm,cross section area,cortex thickness,and number and area of stalk vascular bundles.ED AH also significantly decreased leaf area by 26.8%among upper leaves and by 13.3%among ear leaves.Additionally,EDAH significantly increased grain yield by 14.3%by increasing kernel number and thousand-kernel weight resulting from optimization of the leaf layer structure and higher bleeding sap levels.Lodging-resistance indicators and yields of 'Xundan20'increased more greatly than those of 'Zhengdan958' under the EDAH treatment.