Establishment And Application Of Critical Nitrogen Concentration Model For Leaf And Spike Organs Of Winter Wheat After Flowering

Nitrogen is one of the essential nutrients for wheat growth and plays an important role in the process of material production,yield building,and quality formation.This study conducted field positioning experiments in the Science and Education Park of Henan Agricultural University,Yuanyang County,Xinxiang City,Henan Province in 2016-2018 and 2019-2021,set 3 irrigation conditions(W0: no irrigation,W1: irrigation once at jointing stage,W2: irrigation once at jointing and flowering stages respectively)and 5 nitrogen application levels(0(N0),90 kg hm-2(N6),180 kg hm-2(N12),270 kg hm-2(N18)and 360 kg hm-2(N24)).The dry matter and nitrogen concentration of spike and leaf were determined at different stages(from flowering to maturity)of wheat,the critical nitrogen dilution(Nc)curve models for spike and leaf of winter wheat at after flowering under different irrigation conditions were constructed.We analyzed the relationship between nitrogen nutrition characteristics and nitrogen nutrient index(NNI)of spike and leaf in wheat after flowering,and grain yield,protein content,protein composition,nitrogen transport and nitrogen efficiency,systematically,which provides a theoretical basis of evaluating yield and nitrogen efficiency and predicting quality in the later stage of wheat growth accurate.The main findings are as follows:1.Effects of water and nitrogen treatments on dry matter and nitrogen concentration of spike and leaves after floweringThe dry matter and nitrogen concentration of spike and leaf after flowering in wheat increased with the increase of irrigation and nitrogen application levels,but there are some differences between species.The increase of nitrogen application rate significantly promoted the nitrogen absorption and dry matter accumulation in spike,The dry matter of Zhoumai 27(V27)and Yumai 49-198(V49-198)treated with N12 had an average increase of 54.6% and 52.5% compared with N0,respectively;The nitrogen concentration of spike increased by 12.08% and 14.1%,respectively.the leaf dry matter of the two cultivars was increased by 52.5% and 49.1%,respectively,under N12 treatment compared with N0,and the increase of nitrogen concentration in leaves was 25.5% and 34.7%,respectively,after flowering.With the improvement of irrigation conditions,the nitrogen concentration and dry matter of spike and leaf showed an increasing trend.Compared with W0,the dry matter of spike of the two varieties increased by 26.2% and 21.1% in W1 treatment,and by 39.4% and 30.1% in W2 treatment;compared with W0,the nitrogen concentration of spike of the two varieties increased by 2.15% and 2.18% in W1 treatment,respectively,the W2 treatment increases were 7.6% and 8.34%,respectively.Compared with W0 treatment,the increase of leaf dry matter in W1 treatment was 16.6% and 15%,respectively,and the increase in W2 treatment was 33.7% and 26.3%,respectively;compared with W0,the leaf nitrogen concentration of the two varieties in W1 increased by 5.6% and 4.9%,respectively.In W2 treatment increases were 12.9% and 12.6%,respectively.2.Establishment of critical nitrogen model for spike and leaf and nitrogen nutrient index under different irrigation conditionsAccording to the principle of critical nitrogen dilution model,the critical nitrogen concentration model(Nc)of spike and leaf after flowering was constructed and the nitrogen nutrient index(NNI)was established.The model between critical nitrogen concentration and biomass in spike after flowering is in the form of a power function Nc=a DM-b,and there are differences in model parameters under different irrigation conditions.(W0: Nc=2.58 DM-0.242;W1: Nc=2.92 DM-0.24;W2: Nc=3.10 DM-0.231).The model between leaf critical nitrogen concentration and biomass conforms to the logarithmic function form(Nc=acln(DM)±b),and there are differences in model parameters under different irrigation conditions(W0: Nc=2.58 DM+1.25;W1: Nc=3.07 DM+0.39;W2: Nc=4.49 DM-1.37).Based on the constructed critical nitrogen curve model,the nitrogen nutrition index NNI of different organs after flowering was established,NNI increased with the increase of nitrogen application rate,and gradually decreased with the growth period.The lower the nitrogen application level,the more obvious the downward trend.Taking NNI=1 as the criterion for evaluating nitrogen application rate suitable for nitrogen nutrition,The optimum nitrogen application rate was 180-270 kg hm-2 under no irrigation conditions,and 270 kg hm-2 under irrigation conditions.3.The relationship between nitrogen nutrient index of spike and leaf and yield,protein content and nitrogen efficiencyThe relationship between NNI and relative yield(RY)of spike and leaf after flowering showed a linear + plateau change.When the NNI of spike is 1.03 without irrigation(W0),RY gets the maximum value,when it is 0.95 under irrigation conditions,RY gets the maximum value.The NNI of after flowering leaf was 1.04 and 0.97,when the highest yield was obtained under no irrigation and irrigation conditions,respectively.There was a quadratic curve relationship between nitrogen transport amount,transport rate,contribution rate and NNI of spike and leaf before flowering.and the transport volume reaches the peak when NNI≥1,the transport rate and contribution rate are at NNI=0.8-0.9;there was a significant negative correlation between nitrogen efficiency(NUE)and NNI of spike and leaf after flowering,the correlation coefficients between NNI and NUE of spike and leaf in different years,periods and water conditions were between 0.6-0.85,0.7-0.82 and 0.6-0.7,respectively.Different years had the highest impact on the NUE-NNI relationship,followed by irrigation treatment,and the period had the smallest impact.The main quality indicators(grain protein and components,wet gluten)were significantly positively correlated with NNI of spike and leaf after flowering,the correlation between NNI of spike and wet gluten,globulin and gliadin was the best,The correlation coefficients are 0.806-0.855,0.751-0.777 and 0.707-0.761,respectively,while albumin and glutenin performed poorly,the correlation coefficients are 0.651-0.692 and 0.550-0.627,respectively;the correlation between NNI of leaf and wet gluten,globulin and gliadin after flowering was slightly worse than that in spike.