Effects Of Water And Nitrogen Regulation And Slow-release Nitrogen Fertilizer Combined With Urea On Growth,Water And Nitrogen Utilization Of Winter Wheat/summer Maize

Guanzhong Plain in Shaanxi province is one of the main production areas of winter wheat and summer maize in China.Slow-release nitrogen fertilizer（SRF）has been widely used because its slow release nitrogen（N）can significantly improve nitrogen use efficiency（NUE）and reduce the risk of non-point source pollution.However,due to the change of climate and environment,the synchronization between N release of SRF and crop N demand is still uncertain,and the high price seriously restricts the sustainable development of agriculture.Therefore,it is important to optimize the application and management of SRF to improve the WUE and NUE of winter wheat/summer maize in Guanzhong region and realize the optimal management of N fertilizer on farmland.This study was conducted from2018-2020,including two experiments.Experiment 1:the effects of N application rate and slow-release N fertilizer combined with urea（U）on winter wheat/summer maize in field were studied.Four N fertilizer types:urea（U）,slow-release nitrogen fertilizer（SRF）,urea and slow-release nitrogen fertilizer mixed with 2:8（UNS1）,urea and slow-release nitrogen fertilizer mixed with 3:7（UNS2）and four N application rates:100 kg/hm²（N1）,160 kg/hm²（N2）,220 kg/hm²（N3）and 280 kg/hm²（N4）were set in winter wheat growing season.Four N fertilier types:urea（U）,slow-release N fertilizer（SRF）,urea and slow-release nitrogen fertilizer mixed with 3:7（UNS1）,urea and slow-release nitrogen fertilizer mixed with 4:6（UNS2）and four N application rates:90 kg/hm²（N1）,120 kg/hm²（N2）,180 kg/hm²（N3）and 240 kg/hm²（N4）were set for the summer maize growing season,all with no N treatment0 kg/hm²（N0）as the control（CK）.The effects of N application rate and slow-release nitrogen fertilizer combined with urea（UNS）on growth physiological indexes,N uptake,distribution and remobilization,soil N environment and NH₃ volatilization of winter wheat/summer maize were studied.Experiment 2:water control and UNS application in maize:to investigate the mechanisms of efficient use of water and N,and the effect of yield increase and stabilization in maize under the effect of irrigation amount:60%ETc（W1）,80%ETc（W2）,100%ETc（W3）and N fertilier types:urea（U）,slow-release nitrogen fertilizer（SRF）,urea and slow-release nitrogen fertilizer mixed with the ratio of 3:7（UNS）.The main results were shown as below:（1）It is proved that the slow-release nitrogen fertilizer/combined application of slow-release nitrogen fertilizer and urea could effectively promote the growth of winter wheat/summer maize,increase yield and economic benefits.The growth and physiological indexes,yield and net income of winter wheat showed SRF>UNS1>UNS2>U.Compared with other treatments,the yield and net income of SRF increased by 13.9%–59.7%and 19.6%–89.8%,respectively.The growth and physiological indexes,yield and net income of summer maize showed UNS1>UNS2>SRF>U,the yield and net income of UNS1 was increased by 12.0%–41.7%and 18.5%–97.8%compared with those in other treatments.The growth physiological indexes,yield and net income of winter wheat first increased and then decreased with the increase of N application rate,reached the maximum at N3.The yield and net income of winter wheat under N3 was increased by5.8%–46.5%and 0.1%–90.8%compared with those in N1,N2 and N4,respectively.The growth physiological indexes,yield and net income of summer maize increased with the increase of N application rate,and reached the maximum at N4.Compared with N1,N2 and N3,the yield and net income of summer maize under N4 was increased by 6.3%–33.2%and1.0%–73.4%,respectively.（2）The relationship between yield and post-blooming/silking N uptake and N remobilization of vegetative organs was analyzed.It was clear that increasing post-blooming/silking N uptake and pre-silking N remobilization of vegetative organs could effectively improve crop yield and NUE.The post-blooming/slking N uptake of winter wheat and summer maize was SRF>UNS1>UNS2>U,and N remobilization of vegetative organs was U>UNS2>UNS1>SRF,which were linearly correlated with yield（R²>0.63）.Compared with other treatments,post-blooming N uptake of winter wheat in SRF was increased by 25.3%–140.7%,and N remobilization of vegetative organs was decreased by 2.8%–9.8%,thereby N accumulation and NUE of winter wheat was increased by 11.2%–48.9%and 4.5%–18.8%,respectively.Compared with U and UNS2,the post-slking N uptake of summer maize in UNS1 was increased by 91.3%and 16.7%,while the N remobilization of vegetative organs was decreased by 10.3%and 3.7%,respectively.In addition,post-slking N uptake of UNS1 was decreased by 10.0%compared with that in SRF,while N remobilization of vegetative organs was increased by 31.2%,thereby N accumulation and NUE of summer maize were increased by 7.3%–32.7%and 10.6%–27.3%,respectively.Through N nutrition index（NNI）and N deficiency model,it was found that the NNI of winter wheat under SRFN3 was about 1,without N deficiency.The NNI of summer maize under UNS1N3 and UNS1N4 fluctuated around 1,without N deficiency.（3）It was elucidated that the N release of slow-release nitrogen fertilizer/combined application of slow-release nitrogen fertilizer and urea could be better synchronized with crop N uptake,thus reducing soil nitrate N residue.The N release rate of SRF and UNS1 was synchronized with N uptake of winter wheat and summer maize（R²>0.92）.The content of nitrate N in 0-40 cm soil layer of winter wheat/summer maize was SRF>UNS1>UNS2>U,under 40 cm depth soil nitrate N content showed U>UNS2>UNS1>SRF.The residual amount of nitrate N in 0-120 cm soil layer of winter wheat showed U>UNS2>UNS1>SRF.Compared with U,UNS1 and UNS2,SRF decreased soil nitrate N residue by 16.9%,3.9%and 11.0%,respectively.The residual amount of nitrate N in 0-200 cm soil layer of summer maize growth season was U>SRF>UNS2>UNS1.Compared with U,UNS2 and SRF,UNS1 decreased soil nitrate N residue by 17.4%,6.4%and 10.9%,respectively.（4）The effects of slow-release nitrogen fertilizer/combined application of slow-release nitrogen fertilizer and urea on ammonia volatilization in field summer maize farmland were clarified,and the relationship between soil environmental indicators and ammonia volatilization flux was analyzed.The NH₃ volatilization flux after base fertilizer was UNS2>UNS1>U>SRF,and SRF significantly reduced the NH₃ volatilization flux within 7 d after base fertilizer compared with U and UNS.After topdressing,the peak NH₃ volatilization flux of U was 8.3 kg/hm²·d（2019）and kg/hm²·d（2020）;NH₃ volatilization flux of other N fertilizer treatments was SRF>UNS1>UNS2.The cumulative NH₃ volatilization was U>SRF>UNS2>UNS1,and the cumulative NH₃ volatilization of UNS1,UNS2 and SRF were decreased by 38.8%,31.4%and 17.2%,respectively,compared with that in U（32.5 kg/hm²）.In addition,the cumulative NH₃ volatilization of N1,N2 and N3 were decreased by 50.9%,41.0%and 29.2%compared with that in N4,respectively.NH₃ volatilization flux in farmland was positively correlated with ammonium N content,p H value and electrical conductivity in 0-20 cm soil layer,and negatively correlated with organic matter content in 0-20 cm soil layer.（5）Comprehensive evaluation of coupling effect of N application rate and slow-release nitrogen fertilizer/combined application of slow-release nitrogen fertilizer on winter wheat/summer maize in field.SRFN3 ranked first in winter wheat growth season,thereby applied slow-release nitrogen fertilizer under 220 kg/hm² could be used as the optimal N management strategy for winter wheat in Guanzhong Plain.During the growing season of summer maize,UNS1N3（urea and slow-release nitrogen fertilizer were mixed in the ratio of 3:7,and N application rate was 180 kg/hm²）was recommended as the most suitable fertilization strategy for summer maize in Guanzhong Plain to ensure high yield and efficiency of summer maize while saving fertilizer and reducing emissions.（6）It was clarified that slow-release N fertilizer with urea can effectively alleviate the stress of water deficit on crop growth and improve WUE and NUE.The post-silking N uptake of maize in UNS was increased by 19.1%compared with that in U,thereby the yield was increased by 18.3%.Compared with SRF,the N remobilization of vegetative organs in UNS was increased by 15.0%,thereby the yield was increased by2.3%.WUE and NUE of UNS was increased by 2.4%-10.9%and 1.0%-4.6%,and the residual nitrate N in soil was decreased by 4.7%-8.7%.W3SRF obtained the maximum dry matter,N accumulation and yield,while there was no significant difference with W3UNS.Maize yield in UNS was about 20%and 5%higher than that in U and SRF under water deficit.Therefore,UNS can be used as an optimizing N fertilizer to increase/stabilize grain yield under deficit irrigation conditions.SRF can be applied to increase grain yield in regions with abundant water resources and rainfall.