Research On Water And Nitrogen Effect Of Winter Wheat/Summer Maize And Nitrogen Fertilizer Decision Of Summer Maize Under Drip Fertigation

The highly intensive cropping system of winter wheat-summer maize rotation plays an important role in ensuring food security of China.Water shortage and unreasonable management of water and fertilizer have not only caused low and unstable crop yield,but also reduced the water-fertilizer use efficiency,leading to a series of environmental problems and severely restricting the sustainable development of the winter wheat-summer maize rotation system.To solve these problems,a field experiment of winter wheat-summer maize rotation with drip fertigation system was carried out in the Guanzhong Plain during2018-2020.The experiment consisted of three water levels(only irrigated at fertilization:RF,deficit irrigation:DI(75%ET_c,ET_c is crop evapotranspiration)and full irrigation:FI(100%ET_c))and four levels of N fertilizer application amounts(no N fertilizer:N0;low N:N1(85kg ha^-1 N in the winter wheat season,90 kg ha^-1 N in the summer maize season);medium N:N2(170 kg ha^-1 N in the winter wheat season,150 kg ha^-1 N in the summer maize season)and high N:N3(255 kg N ha^-1 applied in the winter wheat season,210 kg N ha^-1 in the summer maize season)),and a conventional water and nitrogen management(90 mm water was irrigated(furrow irrigation)at overwintering and jointing period of winter wheat and jointing stage of summer maize,255 kg N ha^-1and 210 kg N ha^-1 was applied for winter wheat and summer maize,respectively)as control.The effects of water and nitrogen levels on the growth,GY and yield components of winter wheat and summer maize under the drip fertigation conditions were studied.The water productivity(WP),nitrogen use efficiency(NUE)and economic benefits of winter wheat,summer maize and winter wheat-summer maize rotation systems were analyzed under different water and nitrogen levels.The ratio of dry matter and nitrogen accumulation in various organs of summer maize to plant dry matter and nitrogen accumulation was clarified as a function of the number of days after emergence.The critical nitrogen concentration dilution curves of summer maize based on the dry matter accumulation and LAI were constructed respectively.The estimation model of aboveground biomass,LAI and leaf nitrogen accumulation(NA_leaf)of summer maize based on hyperspectral reflectance was explored.Based on the above analysis,a decision model of nitrogen fertilizer application for summer maize under drip fertigation was formed.The main research results obtained are as follows:(1)The effects of water and nitrogen application rates on the grain yield,yield components,and economic benefits of winter wheat and summer maize were explored under the drip fertigation.The results of a 3-year summer maize field experiment showed that the nitrogen application rate had a highly significant effect on the ear length(EL),bald tip length(BTL),number of ear row(ER)and row kernel(KN),100-kernel weight(HKW)and GY of summer maize(P<0.01),but the irrigation amount and interaction of water and nitrogen had different effects on the GY and yield components of summer maize in different years.In the range of0?150 kg ha^-1 nitrogen application rate,EL,ER,KN and HKW of summer maize all increase with the increasing nitrogen application rate,but the BTL decreased with the increase of the nitrogen application rate.There was insignificant difference between N2 and N3 in EL,BTL,ER,KN and HKW(P>0.05).DIN2 treatment achieved the highest or higher GY in 2018,2019 and 2020.Compared with the CK treatment,the GY of DIN2 increased by 48.4%,29.8%and 30.5%in 2018,2019 and 2020,respectively,and the net income incresed by 36.7%and39.7%in 2019 and 2020,respectively.The results of a 2-year winter wheat field experiment showed that the nitrogen application rate had an extremely significant effects on the maximum tiller density(MTD),tiller number per plant(TP),effective tiller rate(ETR),spike density(SD),grain number per spike(GN),thousand-kernel weight(TKW)and GY of winter wheat(P<0.01).The effects of irrigation amount on SD,GN,TKW and GY of winter wheat all reached significant(P<0.05)or extremely significant levels(P<0.05).The interaction effects of water and nitrogen had insignificant effects on SD and TKW(P>0.05),but had extremly significant effects on GN and GY of winter wheat(P<0.01).In the range of nitrogen application rate of 0?170 kg ha^-1,the MTD,SD and GN of winter wheat increased with the increase of nitrogen application rate,but the TKW decreased with the increase of nitrogen application rate.There was insignificant difference between the basic seedling number(BSN),TP,SD,GN,TKW and GY of winter wheat at N2 and N3 treatments(P>0.05).In 2018-2019 and 2019-2020,the maximum GY of winter wheat was 9.1 t ha^-1 and 9.3 t ha^-1 obtained at DIN2 treatment.Compared with CK treatment,the GY increased by 43.8%and 56.4%,and the net income increased by 82.8%and 119.2%in 2018-2019 and 2019-2020,respectively.2)The optimal intervals of water consumption and nitrogen application for high GY and high economic benefits of winter wheat,summer maize,and winter wheat-summer maize rotation system were put forward.The response surface methodology was used to determine the optimal water consumption and nitrogen application rate based on binary quadratic regression analysis.The results showed that the GY and net income can synchronously achieve 95%?100%maximum values when the water consumption ranged from 434?496 mm,458?500 mm and 885?949mm,and the nitrogen application rate ranged from 165?211 kg ha^-1,187?250 kg ha^-1 and310?408 kg ha^-1 for winter wheat,summer maize and winter wheat-summer maize rotation system,respectively.(3)Soil water distribution and soil nitrate residual was clarified under different irrigation and nitrogen management strategies.More than 90 mm soil water in the 0?320 cm soil layer was consumed by winter wheat,and the soil water consumption followed the order of RFN2>DIN2>CK>FIN2.The soil water consumption can be replenished by irrigation and precipitation during the summer maize season,but the soil water in 180?260 cm under RFN2 was significantly lower than that in the other treatments,which could not be fully replenished.In addition,this study found that the water productivity of winter wheat calculated by considering the difference in soil water storage of 0?120 cm soil layer(WP₁₂₀)is larger than the water productivity calculated by considering the soil layer of 0?320 cm(WP₃₂₀).The WP₁₂₀ of summer maize is lower than the WP₃₂₀.However,from the perspective of the rotation year of the winter wheat-summer maize,WP₁₂₀and WP₃₂₀ had insignificant difference.Compared with CK,the nitrogen application amount of drip fertigation(RFN2,DIN2and FIN2)redeced about 30%,but the soil nitrate-N residual in the 0?180 cm soil layer had insignificant difference among the treatments at harvest of winter wheat and summer maize.The plant nitrogen accumulation of CK was significantly lower than in other treatments,which indicated that the large amount nitrogen was losses under CK treatement.The soil nitrate-N residual rate of CK(less than 40%and 30%at winter wheat and summer maize harvest)was significantly lower than that of drip fertigation(more than 50%and 40%at winter wheat and summer maize harvest)in the 0?60 cm soil profile,but significantly higher than that in the 60?180 cm soil profile.Therefore,drip fertigation with reduced nitrogen application could reduce the risk of nitrogen leaching in Guanzhong Plain.(4)The functional relationship between the ratio of organ dry matter/nitrogen accumulation to plant dry matter/nitrogen accumulation with the days after emergence of summer maize and the leaf critical nitrogen concentration dilution curve of summer maize based on leaf area index and above-ground dry matter accumulation wereconstracted.The ratio of the leaf dry matter/nitrogen accumulation to the plant dry matter/nitrogen accumulation gradually decreased with the increase of the number of days after emergence.The ratio of the stem dry matter/nitrogen accumulation to the plant dry matter/nitrogen accumulation first increased and then decreased.After ear formation,the ratio of ear dry matter/nitrogen accumulation to plant dry matter/nitrogen accumulation continued to increase.Under the sufficient water and nitrogen condition,the ratio of the organ dry matter/nitrogen accumulation to the plant dry matter/nitrogen accumulation is relatively stable.Therefore,the functional relationship between the ration of organ dry matter/nitrogen accumulation to plant total accumulation with the days after emergence of summer maize was constructed.Leaf critical nitrogen concentration dilution curve of summer maize model was constructed based on the LAI and the above-ground dry matter accumulation.It was found that the parameter of the critical nitrogen concentration dilution curve had insignificant difference under deficit irrigation and full irrigation condition(P>0.05).Based on this,we obtained the unified leaf critical nitrogen concentration dilution curve based on leaf area index and above-ground dry matter under irrigation treatment.(5)The estimation model of aboveground biomass,leaf area index and leaf nitrogen accumulation was constracted based on summer maize canopy hyperspectral data.Partial least squares regression(PLS),extreme learning machine(ELM),random forest(RF)and stacked ensemble extreme learning machine(SE_PLS?ELM,based on the PLS stacked ensemble strategy)were used to construct the estimation model of aboveground dry matter,LAI and NA_leaf of summer maize.The estimation models of PLS and ELM had low accuracy.The estimation model of aboveground dry matter,LAI and NA_leaf based on RF and SE_PLS?ELM had higher estimation accuracy,and the performance of SE_PLS?ELM model was particularly outstanding.The R² of validation set of aboveground dry matter,LAI and NA_leafestimation model based on SE_PLS?ELM model were 0.955,0.969 and 0.831,respectively;the RMSE were 307.3 kg ha^-1,0.24 cm² cm^-2 and 11.20 kg ha^-1 and the residual predictive deviation(RPD)were 4.66,5.30 and 2.54,respectively.(6)A nitrogen fertilizer supply model for summer maize was proposed under drip fertigation condition.A nitrogen fertilizer supply model was proposed by integrating the relationship between the ratio of the leaf dry matter/nitrogen accumulation to the plant dry matter/nitrogen accumulation and days after emergence,the leaf nitrogen concentration dilution curve based on the dry matter accumulation,the estimation model of above-ground dry matter and leaf nitrogen accumulation and nitrogen use efficiency under drip fertigation condition.