| The study was carried out in College of Water Resources and Architectural Engineering, Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education Northwest A&F University, Yangling, Shaanxi China(108°24′E, 34°20′N) from 2013~2015. It included two experiments. Experiment 1:Six main stream summer maize varieties(ZD958、ZK11、XY335、WK2、QD8 and QL11) and four nitrogen levels N0(0), N1(86 kg/hm2), N2(172 kg/hm2) and N3(258 kg/hm2) were applied to the study. Experiment 2:Six main stream winter wheat varieties(XY22、XN979、XM23、LX988、WN148 and XN509) and four nitrogen levels N0(0), N1(105 kg/hm2), N2(210 kg/hm2) and N3(315 kg/hm2)were applied to the study. We investigated the effect of different nitrogen application rate on growth,physiology dry matter(nitrogen) accumulation and remobilization, soil water and nitrogen accumulation of different wheat and maize varieties, results showed:(1) Effect of different N application rate on growth and physiology of summer maize and winter wheatLeaf area index, total chlorophyll and net photosynthetic rate increased with increasing of N application rate. During the main growth stages of summer maize and winter wheat, differences exist during the whole growth period between the related indexes of different variety summer maize, while post-flowering of winter wheat. N application significantly increased the summer maize/winter wheat grain yield, but excessive nitrogen couldn’t increase grain yield, and even lower. Based on the maximum yield of differences of N application, In general was between 86~172 kg/hm2, while winter wheat was between 105~210 kg/hm2. The yield of different genotypes summer maize overall performanced, ZD958=XY335>ZK11=WK2=QL11>QD8;The winter wheat yield showed, XY22=XN509>LX988=XN979>XM23=WN148.(2) Effect of different N application rate on dry matter(nitrogen) accumulation and remobilization of summer maize and winter wheatDry matter(nitrogen) accumulation increased with increasing of N application rate of summer maize and winter wheat. Negative vegetative dry matter remobilization likely appeared in summer maize under dry farming condition, it mans vegetative dry matter increased but decrease after silking stage. This may affect the sources of the dry matter weight of grain. Vegetative dry matter(nitrogen) remobilization efficiency and its contribution to grain dry weight decreased with increasing of N application rate, From another point of view, contribution of post-silking dry matter(nitrogen) accumulation to grain dry weight increased with increasing of N application rate. Showed Negative correlation between Vegetative nitrogen remobilization efficiency and aboveground N accumulation, it means that choosing the variety with low Vegetative nitrogen remobilization efficiency could improve N use efficiency Significantly.(3) Effect of different N application rate on N utilization efficiency of summer maize and winter wheatN uptake efficiency, N utilization efficiency and N use efficiency decreased with increasing of N application rate of summer maize and winter wheat under dry farming condition. Value of N use efficiency was 13.3~30.5 kg/kg of summer maize and 18.1~27.3kg/kg of winter wheat. Researching the relationship between N use efficiency and nitrogen nutrition characters of summer maize and winter wheat by means of correlation analysis, the resulted showed positive correlation between N use efficiency and N uptake, aboveground dry matter(nitrogen) accumulation; in addition, negative correlation with vegetative nitrogen remobilization efficiency, but no correlation with grain N concentration;The winter wheat showed the opposite phenomenon.(4)High grain yield and nitrogen efficient varietiesThrough clustering analysis, divided the grain yield and N use efficiency of different genotypes summer maize / winter, the results showed that ZD958 and XY335 was based on the high yield and nitrogen use efficiency of summer maize varieties, the value of grain yield and nitrogen use efficiency of the two variety was(6483.0 kg/ha,19.9kg/kg) and(6358.1 kg/ha,20.1kg/kg);while the variety of ZD958 and XY335 was based on the high yield and nitrogen use efficiency of summer maize, the value of grain yield and nitrogen use efficiency of the two variety was(6586.9 kg/ha,24.2 kg/kg) and(6472.3kg/ha,22.5 kg/kg).(5)Effect of different N application rate on water consumption and nitrate nitrogen accumulation of summer maize/winter wheatWater consumption of summer maize appeared interannualy changes with the change of N application; while Water consumption of winter wheat increased with N application rate. Nitrate nitrogen accumulation increased with N application rate during the summer maize/winter wheat growing season. We established the relationship diagram among N application rate, grain yield and nitrate nitrogen residual, results showed that grain yield couldn’t increase linearly with increasing of N rates, But nitrate nitrogen accumulation showed linearly increasing trend in mature period, Based on the maximum summer maize yield, N application rate range was 86~172 kg/ hm2. The nitrate nitrogen accumulation of corresponding 1 m soil was 166.5~265.9 kg/hm2. Based on the maximum winter wheat yield, N application rate range was 105~210 kg/ hm2. The nitrate nitrogen accumulation of corresponding 1 m soil was 111.5~177.4 kg/hm2.(6) Determination of critical nitrogen dilution curve for summer maize/winter wheat in Guanzhong PlainResult showed there were exponential relationships between the critical nitrogen concentration and the maximum aboveground biomass during both years, which was expressed as Nc=21.91DM-0.31(DM≥1.15 t/ha) and Nc=22.3 g/kg(DM<1.15 t/ha) in the normal year(2013a), and Nc=21.91DM-0.14(DM≥0.63 t/ha) and Nc=26.5 g/kg(DM<0.63 t/ha) in the drought year(2014a). The hydrological year did not change the values of the parameter a, but the parameter b in the drought year(2014a) was significantly smaller than that in the normal year(2013a). By analyzing the NNI and its relationship with the relative yield(RY), 172 kg/hm2 was considered as the optimal amount of nitrogen for high maize production. the critical nitrogen dilution curve(Nc) and nitrogen nutrition index(NNI) established in this study can be used to diagnose the nitrogen status plants and guide the precise application of nitrogen in the normal and drought years as a reliable indication.Result showed there were exponential relationships between the critical nitrogen concentration and the maximum leaf dry matter, which was expressed as Nc=3.96LDM-0.14(LDM≥0.56 t/ha) and Nc=4.32%(LDM < 0.56 t/ha), nitrogen nutrition index(NNI) calculated by critical nitrogen dilution curve(Nc), Results show that, Under the N0 and N1 N application rate, NNI<1,means nitrogen nutrition deficiency, Under the N3 application rate, NNI>1, it means nitrogen nutrition excess, while Under the N2 application rate, NNI≈1, it means nitrogen nutrition suitable, By analyzing the NNI and its relationship with the relative yield(RY), 105~210kg/hm2 was considered as the optimal amount of nitrogen for high winter production. Nitrogen deficiency or excess can reduce crop yields. |
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