Optimization Of Water And Nitrogen Use Efifciencies In Winter Wheat And Summer Maize Cropping System In North China Plain

The North China Plain (NCP) produces over20%of the national food-grain,with a dominant croppingsystem of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) grown in rotation.However, in the pursuit of high yield, the overuse of nitrogen and water in winter wheat and summermaize rotation system (WW-SM) was very common, which had already led to low nitrogen and wateruse efficiency, meanwhile, exacerbated the water scarcity and environment pollution. It is imperative forfood security and sustainable agriculture to search on water and N use as well as the relevant grain yieldin WW-SM and then find an optimal water and nitrogen measures (OWNM), under which water and Nuse efficiency were increased, while high crop yields obtained and the harm to environment byfertilization was diminished.In order to elucidate water and N use efficiency and crop yields under OWNM measures in WW-SM inNCP, field plot trials combined with micro-plot experiment with15N tracing from2007to2010werecarried out in Mazhuang Experimental Station in Xinji of Hebei province. The experiment design was asfollow: for winter wheat,3irrigation treatments were included: irrigation3times as conventional (I3),2times irrigation with33%of water saved (I2), and irrigation once with67%of water saved (I1). Undereach irrigation condition,5fertilization levels were designed as: no fertilization (CK),0(N0),150(N150),210(N210),270(N270, the conventional level) kg N ha^-1with same amount of phosphorus (P)and potassium (K), respectively. For summer maize, under the condition of irrigation twice(I2),6fertilization treatments were included: no fertilization(CK),0(N0),90(N90),180(N180), and270(N270)kg N ha^-1with the same amount of P and K, and one treatment of180kg N ha^-1applied once (N180y),N fertilizer of other treatments applied twice. And under the condition of irrigation once (I1), there were3fertilization treatments such as: no fertilization (CK), only P and K fertilizer (N0) and180kg N ha^-1fertilizer applied once (N180y). Micro-plot experiment design was the same as the nitrogen fertilizationtreatments in the field plot, which was divided into2treatments of basal15N-urea labeled, with15N-ureatopdressed and labeled. Research mainly on the N absorption regularity, N residual in soil profile, grainyield, water and N use efficiency under OWNM measures in winter wheat and summer maize rotationsystem in NCP. The main results are as follows:(1) The fates of15N labeled urea in winter wheat and summer maize under different N rates andirrigations have been made clear. The urea-15N fates including N uptake by wheat plant (63.2¹26.2kgN ha^-1), soil residual N (54.9⁷4.5kg N ha^-1) and the unaccounted N losses (20.3⁸1.3kg N ha^-1)significantly increased as the fertilizer N rose. While the residual N and unaccounted N losses werenotably decreased by17.0%and37.8%, respectively, under N210(reducing22%of N), compared tothat of N270. And there were no significant differences between treatment I2and I3. In addition, thelabeled residual-15N absorbed by the second and the third successive crops were8.4²2.1,3.8⁷.2kg Nha^-1, respectively. The urea-15N fates including N uptake by maize plant (43.4¹04.8kg N ha^-1), soilresidual N (44.0¹37.3kg N ha^-1) and the unaccounted N losses (2.6²7.9kg N ha^-1) significantly increased as the fertilizer N rose. In addition to the N recovered in the first maize crop, a further of6.7¹8.7kg N ha^-1was absorbed by the following wheat. An additional of2.0⁵.7kg N ha^-1wasabsorbed by the second maize crop grown after the wheat.(2) The nitrogen use efficiency in winter wheat and summer maize under different N rates andirrigations has been verified. The nitrogen recovery efficiency (RE) were ranged from4.8%to32.5%,from20.5%to59.9%and from21.8%to44.2%for elongation stage, grain filling stage and maturitystage of wheat season, respectively, all of which were enhanced as irrigation times added. And the REunder I2(33%of water saved) was32.0%in maturity stage, significantly down by12.1%, incomparison with that of conventional irrigation treatment (I3). However, nitrogen only had a significanteffect on RE in maturity stage, and RE in maturity stage of N210(34.8%) were23.8%higher than thatof N270(28.1%). The RE of maize were3.9%⁴0.5%,5.1%⁴0.6%,3.8⁴8.0%for spike formulationstage, silk stage and maturity stage, respectively. Under the condition of I2, reducing33%of N (I2N210)had no significant affect on RE in the3growing stages, when compared to those under conventional Nrate (I2N270). Meanwhile, at the N rate of180kg N ha^-1, spilt applications of fertilizer N (I2N180)significantly increased RE in spike formulation stage, compared with applied fertilizer N once beforeseeding (I2N180y). However, irrigations did not significant affect RE in the3growing stages.(3) Gotten a further clarification of water use efficiency (WUE) based on biomass and grain yield(WUEgrain) in winter wheat and summer maize under different N rates and irrigation. The water useefficiency based on wheat biomass in different growing stages ranked as: elongation to grain fillingstage>grain filling to maturity>seeding to elongation. And the WUE based on whole biomass andWUEgrain were significantly increased as the fertilizer N increased as the fertilizer N less than210kgN ha^-1, while there were no significant increase when the fertilizer N over210kg N ha^-1. The WUEgrainand WUE based on whole biomass of I2were significantly increased, when compared to those of I3.For maize, the WUE based on biomass in4growing periods ranked as: silk stage to maturity>spikeformulation stage to silk stage>seedling stage to spike formulation stage>sowing to seedling stage. Nrates had a significant effect on WUEgrain, however, there were no significant differences betweenI2N180and I2N270.(4) The grain yields of winter wheat and summer maize under different N rates and irrigations weredefinite. The wheat grain yields across treatments ranged from3267to8789kg ha^-1, with the meanreaching7847kg ha^-1under the condition of reducing22%of fertilizer N (N210),0.4%higher (P>0.05)compared to that of N270(7816kg ha^-1). Meanwhile, the grain yield was not significantly decreasedunder condition of I2, in comparison with that under I3. For maize, the grain yield across treatmentsranged from5122to9787kg ha^-1. By reducing33%of fertilizer N (I2N180), the mean grain yieldreached to9201kg ha^-1,2.4%less (P<0.05) than that of I2N270(P>0.05).(5) Gained a preliminary idea of the optimal water and nitrogen measures (OWNM) and their economicbenefits. The optimal measures were I2N210and I2N180for winter wheat and summer maize, underwhich the net benefits were7887and13113yuan ha^-1year-1,14.7%and0.03%higher than those underconventional measures, respectively. The total income was increased by5.1%under the OWNM (21000 yuan ha^-1year-1) as compare to conventional measures.In conclusion, the water and nitrogen use of winter wheat and summer maize were made clear inWW-SM cropping system under different N rates and irrigations, suggesting that the combination ofI2N210for wheat and I2N180for maize was the optimal measure for WW-SM cropping system, underwhich higher grain yields and higher net income kept, as well as enhanced water and nitrogen useefficiency gained, moreover,20%of water and28%of nitrogen were saved. Therefore, it provided apowerful reference for the soil water and N management in winter wheat and summer maize rotationsystem in NCP.