Coupling Effect Of Water And Nitrogen On Seed Maize Under Alternate Partial Root Zone Irrigation

In the face of agricultural resources waste and the environments pollution due to low efficient use of fertilizer and water in worldwide,how to explore the adaptive potential of crop-self to nutrients,water and so on environmental factor through jointly regulate effect of water and nutrient has rousedintensiveattentions.Alternate partial root zone irrigation(APRI)is considered as water-saving irrigation method and has been intensively practiced.However,little information is available on coupling effect of water and nutrient on crop production under APRI.In order to make APRI better practice in crop production,it is necessary to system study on coupling effect of water and nitrogen under APRI.A field study was conducted during the 2013 and 2014 growing seasons at Wuwei Experimental Station for Efficient Use of Crop Water,Ministry of Agriculture,northwest Chinausing seed maize Golden northwest No.22 as experimental material.Furrow irrigation was adopted and all ridges were built in awest-east direction.First,we investigated the environmentsof soil water and soil nutrient and the crop growth undervarying irrigation and nitrogen supply methods.Irrigation methods included conventional furrow irrigation(CI),alternate furrowirrigation(AI)and fixed furrowirrigation(FI).Nitrogen supply methods included conventional nitrogen supply(CN),alternate nitrogen supply(AN)and fixed nitrogen supply(FN).On this basis,we studied the effects of varying low irrigation limits(55%Fc,65%Fc and 75%Fc)and nitrogen rates(100,200 and 300 kg N hm-2,designated N1,N2 and N3,respectively)on the crop growth and its consumption of water and uptake of nitrogen under APRI.Meanwhile,we analyzed the law of water use by the crop and crop coefficient of different irrigation regimes(full irrigation,mild water stress during seeding stage,serve water stress during seeding stage,mild water stress during ear stage,serve water stress during ear stage,mild water stress during flower stage and serve water stress during flower stage,designated CK,T1,T2,T3,T4,T5 and T6,respectively);established crop production function,and obtained the appropriateirrigation regime under APRI for seed maize.Following are the main achievements of this thesis:(1)We studied the progress of dry matter accumulation duringseed maize growing season and measured the crop yield and water utilization by the cropunder varying irrigation and nitrogen supply methods.The results showed that,the progress of dry matter accumulation inseed maize was following Logistic equation X=K?1+ae-bt for all treatments.However,the upper limit of maximum dry matter accumulation K value was varied among the treatments.For three rrigation methods,K of AN and CN weregreater than K of FN.For three nitrogen supply methods,the greatest K was found in AI,followed by CI and FI.AI coupled with CN(AC)and AI coupled with AN(supplied water and nitrogen within a same furrow,AAT)had the greatest K among the treatments.Compared to the other irrigation and nitrogen supply methods,dry matter of maize grain yield and the ratio of it to total dry matter for AC,AAT and AI coupled with AN(supplied water and nitrogen in different furrows,AAY)were obviously increased.Similar results were observed for ear numbers,grain yield,harvest index and water use efficiency(WUE)of maize.These indicate that alternate partial root zone irrigation coupled with alternate nitrogen supply(supplied water and nitrogen within a same furrow)or conventional nitrogen supply is useful to improve grain yield and water use efficiency of seed maize.(2)We studiedsoil water content and soil nitrate content of south,north and under the plant in 0-100 cm soil profile(20 cm as an interval)at joint,spike bell,tasseling,filling and maturity of seed maizeundervarying irrigation and nitrogen supply methods.The results showed that,in most cases,for three irrigation methods,soil water content of south and north of the plant before irrigation wereonly influenced by differentnitrogen supply methods.There had no significant difference insoil water content betweensouth and north of the plant forCN and AN.And,soil water content under nitrogen supplied side was greater than that under no-nitrogen supplied side for FN under CI.In most cases,soil nitrate content under nitrogen supplied side was greater than that under no-nitrogen supplied side in any irrigation method for FN.AI enhanced soil nitrate content under the plant in 0-40 cm soil profile compared to CI in any nitrogen supply method.Compared to other irrigation and nitrogen supply methods,soil nitrate content between south and north plant had no significant differencefor AC,AAT and AAY treatments,and these treatments hadthe greater soil nitrate content in 0-40 cm soil profile,suggesting that alternate partial root zone irrigation coupled with alternate nitrogen supply or conventional nitrogen supply not only brought uniform distribution of soil nitrate but also maintained soil nitrate in 0-40 cm soil profile for a longer time.(3)We studied effects of varying irrigation and nitrogen supply methods onroot growth of seed maize and its changes following maize growth stages.The results showed that there was no significant difference inroot length density between south and north of the plant in 0-40 cm soil profile at filling stage forAI or CI coupled with AN or CN.However,root length density between south and north of the plant had a significant difference for FI coupled with FN.In most cases,in 0-40 cm soil profile,for three nitrogen supply methods,root length density under the plant of AI was significantly greater than that of CI and FI.For three irrigation methods,root length density under the plant of FN was significantly smaller than that of CN and AN.Root length density under the plant of AAT,AAY and AC treatments weregreatest among the treatments.In most cases,AC,AAT and AAY treatments had the greatest total root length,root dry weight and root surface area in 0-100 cm soil profile among the treatments.These indicate that alternate partial root zone irrigation coupled with alternate nitrogen supply or conventional nitrogen supply not only brought a relative uniform distribution of root,but also enhanced root growth.The relationship between grain yield and root length density X1 (cm cm-3),root dry weight density X2 (mg cm-3),and root surface area density X3 (cm2 cm-3)in 0-40 cm soil profile at filling stage of seed maize accorded with exponential model Y=2102X11.03X20.92X30.45 as well aspolynomial model Y=2272.98+ 1937.21X1+3553.85X2-2581.76X1X2.(4)We studiednitrogen uptake and use by seed maizeunder varying irrigation and nitrogen supply methods,and found thatnitrogen uptake amount by the crop and nitrogen use efficiency(NUE)was significantly increased by AI compared to CI in any nitrogen supply method.Nitrogen uptake amount by the crop and NUE weresignificantly reduced by FN compared to the other two nitrogen supply methods in any irrigation method.AAT and AC treatments had the greatest NUE among the treatments.Therefore,alternate partial root zone irrigation coupled with alternate nitrogen supply(supplied water and nitrogen within a same furrow)or conventional nitrogen supply is useful to improve nitrogen use efficiency of seed maize.Using 15 N tracer technology,the results showed that,underAN or CN,fertilizer nitrogen uptake bythe crop of AI was significantly increased if compared to CI.Meanwhile,fertilizer nitrogen absorptive rate(26.57%-29.01%)by the crop and its lossrate(25.78%-27.41%)were comparable for AI.Whereas the absorptive rate(22.93%-23.78%)was obviously lower than the loss rate(34.37%-34.88%)for CI.These results indicate that alternate partial root zone irrigation enhanced the ability of seed maize to absorb the fertilizer nitrogen and reduced the loss of fertilizer nitrogen if compared to conventional furrow irrigation.(5)We studiedseed maize shoot growth parameters,grain yieldand its formation of varying low irrigation limits and nitrogen rates under APRI.The results showed that,for three nitrogen rates,crop growth rate,plant height,stem diameter and leaf area indexof 65%Fc were significantly greater than thoseof 55%Fc.For three low irrigation limits,the abovementioned parameters of N2 were significantly greater than thoseof N1.75%Fc coupled with N2 or N3 achieved the greatest mentioned crop parameters.Similar results were observedforbiomass,grain yield,harvest index,ears number and kernels per spike.These indicate that 75%Fc coupled with 200 or 300 kg N hm-2 could maintain vigorous shoot growth and achieved thehighestgrain yield of seed maize under APRI.A significant interaction of low irrigation limit and nitrogen rateoccurredon maize biomass and grain yield.For N1 treatments,increasing low irrigation limits ranged from 55% to 65%Fc could improve the biomass and grain yield.Similarly,increasing nitrogen rates could improve grain yield for 75%Fc.However,increasing nitrogen rates over 200 kg N hm-2 could not enhance the biomass and grain yield for 55%Fc.These indicate that there is a compensate effect between nitrogen rate and water supply level within a certain range,only coordinate of low irrigation limit and nitrogen rate can improve grain yield of seed maize under APRI.(6)We studiedwater use and nitrogen uptake by the crop of varying low irrigation limits and nitrogen rates under APRI.The results showed that,for three nitrogen rates,65%Fc had the greatest WUE,followed by 75%Fc and 55%Fc.For three low irrigation limits,WUE of N2 and N3 were significantly greater than WUE of N1.65%Fc coupled with N2 or N3 achieved the greatest WUE among the treatments.Nitrogen uptake amount and NUE between 65%Fc and 75%Fc werecomparable while they both significantly higher than those of 55%Fc in any nitrogen rate.Nitrogen uptake amount of N2 and N3 weresignificantly greater than that of N1 in any low irrigation limit.With the increasing nitrogen rates,NUE was significantly reduced while residual soil nitrate in 0-100 cm soil profile after harvest was significantly increased.Thus,coordinated low irrigation limit and nitrogen rate isvital for improving use efficiency of water and nitrogen under APRI.65%Fc coupled with 200 kg N hm-2 could below the premise that coordinate grain yield,and had a relatively higher water-and nitrogen-use efficiency as well as reduced residual soil nitrate in0-100 cm soil profile after harvest under APRI.(7)We analyzed water consumption,crop coefficient Kc,grain yield and WUE in seed maize of different irrigation regimes under APRI.The results showed that,both intensity of water consumption and Kc werelowered by water stress inany growth stage.Compared to CK,the grain yield of T2,T3,T4,T5 and T6 treatments weresignificantly reduced while that of T1 was comparable.However,water consumption under T1 was significantly reduced by20.41% compared with CK.These indicate that mild water stress at seedling stage could obviously improve water use efficiency of seed maize under APRI.Based on Jensen model,we obtained sensitivity index ?i for during planting to joint,joint to tasseling,tasseling to filling,and filling to maturity of seed maize was-0.02,0.72,0.60 and 0.13,respectively,indicating that the level of sensitivity of seed maize to water stress during joint to tasseling and tasseling to filling aremuch larger than that duringfilling to maturity and planting to joint.We obtained economic irrigation norm 2400 m3 hm-2 through synthesizing crop water consumption law,grain yield,WUE,and the crop production function at different growth stages of seed maize under APRI.A dynamic programming method was applied to establish optimizing irrigation regime for seed maize under APRI.The irrigation regime are as following:using irrigation quota180,330 and 195m3 hm-2 for before joint,during joint to filling and during filling to maturity of seed maize,respectively;and irrigate three,two and two times at before joint,during joint to filling and during filling to maturity of seed maize,respectively.