Effects Of Water And Temperature In Winter Wheat And Interactions Of Nitrogen And Sulfur In Summer Maize And Their Optimal Regulation

Water deficit and periodic high temperature are two factors limiting wheat production in the arid and semi-arid regions of Northwest China,while excessive fertilization and nutrient imbalance are major factors affecting maize production.However,few studies were conducted on water and temperature dynamics and system regulation of soil-wheat system.And little is known about the effects of sulfur（S）,interactions of nitrogen（N）and S,and their optimal regulation in maize production.Therefore,field experiments were carried out to investigate the effects of tillage systems on regulation of water,temperature,and light use in winter wheat system.And effects of N and S in summer maize and physiological and biochemical mechanisms were studied in field and sand culture experiments.The comprehensive diagnostic index system of N and S in summer maize was also determined by means of stoichiometry.In addition,the relationships among growth factors were investigated through model simulation to provide theoretical and technical basis for improving the productivity and resource use efficiency of winter wheat and summer maize.Field experiments about water and temperature regulation in winter wheat were conducted in 2012-2013 and 2013-2014.Six tillage systems were included,i.e.,flat tillage without mulch（FT）,flat tillage mulched with stalk（FTs）,flat tillage mulched with plastic-film（FTp）,ridge tillage without mulch（RT）,ridge tillage mulched with plastic-film（RTp）,and ridge tillage mulched with plastic-film and stalk（RTps）.The dynamics of water and temperature in wheat,responses of morphological and physiological traits to water and temperature,responses of soil N availability to water and temperature,and relationships between wheat yield and water and temperature status were studied.Pot experiments（sand culture）about N and S regulation in summer maize were conducted in 2015.And the 25treatments were the combination of five N levels（0,7.5,15,22.5,and 30 mM）and five S levels（0,1,2,3,and 4 mM）.In addition,field experiments about N and S regulation in summer maize were conducted in 2015 and 2016.And the 16 treatments consisted of the combination of four N application rates(0,90,180,and 270 kg N ha^-1)and four S application rates(0,45,90,and 135 kg S ha^-1).The uptake of N and S in maize,assimilation of N and S,responses of morphological traits and yield to N and S fertilizer,optimal N and S concentration in maize parts,and diagnostic indicators were investigated.The main results are summarized as follows:（1）Ridge tillage and mulching regulated the temperature and moisture of soil-canopy system,and thus delayed the dry matter translocation,improved the dry matter translocation efficiency,optimized yield components,and then increased wheat grain yield.The FTp and RTps systems were better than other tillage system in improving wheat grain yield.（2）Water and N use in wheat were improved with ridge tillage and mulching.Ridge tillage and mulching reduced evapotranspiration and improved water use efficiency.Ridge tillage and mulching increased wheat N uptake and grain crude protein yield.（3）During jointing to maturity stage,mass-based canopy moisture gradually decreased,while area-based canopy moisture increased and then decreased.Mass-based canopy moisture and area-based canopy moisture were positively correlated with grain yield.Ridge tillage and mulching improved wheat water status,and increased mass-based and area-based canopy moisture during jointing to milking stage.（4）Canopy temperature was negatively correlated with grain yield,while canopy temperature depression was positively correlated with grain yield.Ridge tillage and mulching reduced canopy temperature and increased canopy temperature depression.（5）The FTp and three ridge tillage systems induced the formation of heterogeneity of temperature,respiration,and water in wheat fields,and thus affected the transformation and availability of soil N and uptake of water and N by wheat.（6）Ridge tillage and mulching tended to increase leaf total chlorophyll,reduced reflectance of visual light,and increased transmittance and absorptance of visual light.And this may favor photosynthesis and alleviate the negative effects of reduced leaf area index on photosynthesis.（7）Maize grain yield generally increased with N and S levels.The effect of N on grain yield was greater than that of S.There were some interactions between N and S.For maize production in Guanzhong Plain,the recommended N and S application rates are 180²00 kg N ha^-1 and 71 kg S ha^-1,respectively.（8）The major N source for maize plants was root uptake,while environmental air was an important S source for maize plants when S was not supplied to root.（9）Application of N and S significantly affected some important enzymes in N and S assimilation,such as nitrate reductase（NR）,glutamine synthetase（GS）,ATP sulfurylase（ATPS）,and O-acetylserine（thiol）lyase（OASTL）.Maize N uptake was correlated with GS and ATPS,while maize S uptake was correlated with GS and OASTL,which indicated that there were synergies between N and S assimilation.The findings provided a new evidence about the interactions between N and S.（10）Leaf at silking stage is suitable for N and S diagnosis in maize.For N and S diagnosis,the recommended critical thresholds are 25.9²9.3 mg N g^-1（leaf total N concentration at silking stage）and 16.3¹9.6（leaf N:S ratio at silking stage）.Overall,water and temperature status in wheat fields can be improved by ridge tillage and mulching practices,and then increase wheat grain yield and enhance water and N use.Maize yield and N and S uptake can be improved by optimizing N and S application rates.The total N concentration and N:S ratio in maize leaves can be used to assess N and S status in maize plants,and then guide N and S management in maize production.