Experiment Of Water And Nitrogen Coupling Effects On Sprinkler-irrigated Winter Wheat

Water and fertilizer are two major resources invested in the farmland ecosystem,and also two limiting factors drawing the highest human attention and receiving the most intensive artificial regulation.There exsit obvious coupling effects between them,which are critical to the growth,yield formation and resource utilization of wheat.However,there are many problems in wheat production,such as excessive irrigation and fertilization with low utilization rate,which have caused a series of ecological and environmental problems.In this paper,three irrigation levels(i.e.,low irrigation level,25 mm,W1;moderate irrigation level,40 mm,W2;high irrigation level,55 mm,W3)and five nitrogen supply levels(i.e.,N0,0 kg/hm~2;N1,80 kg/hm~2;N2,180 kg/hm~2,N3,240 kg/hm~2,N4,300 kg/hm~2)were designed to optimize the management of crop irrigation and fertilization.The effects of irrigation,nitrogen application and their interaction on soil water and nitrogen distribution,photosynthetic physiology,dry matter accumulation,grain filling characteristics,yield and water and nitrogen use efficiency of winter wheat were explored under sprinkler irrigation in the south central areas of Huang-Huai-Hai Plain.Main results were presented as follows:(1)Coupling N2 and N3 levels with optimal irrgation supply was favorite to crop growth,which increased the soil water storage use efficiency,promoted the absorption and utilization of water from deep soil,and improved soil water content in plough layer.N2～N3 levels could adequately satisfiy the demand of N absorption during the whole growth period of wheat.The movement of nitrate nitrogen to the deep layer was found to be significantly positively associated with growth process and different irrigation and fertilization rates.Variations in ammonium nitrogen content significantly fluctuated with crop growth proceeding.As the irrigation rates increased,ammonium nitrogen decreased at the same nitrogen application level.Fertilization and irrigation might not affect the movement of soil ammonium nitrogen to deep layer.(2)Deficit water supply accelerated the growth and maturity.of wheat apparently,shortening its life cycle.High nitrogen application decreased LAI slowly and delayed the premature senescence of wheat leaves.At grain-filling stage,Pn(photosynthetic rate),Tr(transpiration rate),and SPAD values of flag leaves increased initially with the nitrogen application increasing and then kept stable,or decreased slightly.Averaged dry matter accumulation of W2 increased by 5.44%,compared to that of W3,while no significant difference between W1 and W3 was observed.Averaged dry matter accumulation of N3 level was highest among N treatments,with an increase of 5.94%compared to the CK(N0).(3)T_e(the grain-filling lasting time)and t_m(the time when maximum filling rate occured)were affected by fertilization significantly,both of which increased first and then decreased as nitrogen application rates increased.T_e at N3 level was longest,with an average of 43.9 d,which was 1.7 d longer than that of N0(zero nitrogen application).Similarly,t_m at N3 level was also largest,with an average of24.6 d,occured 3.0 d later than N0 did.The largest t_m value was obtained at the W2N3 treatment,which happened 5.0 d later than W1N0 treatment did.Fertilization and irrigation exerted extremely significant or significant effects on yield and its components.Moderate water and fertilizer application rate was suitable to improve the utilization of irrigation water,whereas the excessive nitrogen application reduced the compensation effect of irrigation water.The highest grain yield and WUE(water use efficiency)were obtained at W2N3 treatment with the maximum of 8960 kg/hm~2 and 2.83 kg/m~3,respectively.In this study,comprehensively taken yield-boosting of wheat,water and nitrogen use efficiency into account,optimal irrigation quota of sprinkler was within 26～35 mm,nitrogen application rate was at193～204 kg/hm~2(basal application 40%and topdressing 60%at jointing stage),which can be recommended as the favorite water and fertilizer resource allocation interval.The result could provide guidance to field water and fertilizer management of sprinkler-irrigated winter wheat in the south central areas of the Huang-Huai Plain.