| In this paper,a two-year field experiment was conducted in Yuzhou,Henan Province from 2017 to 2019.Six genotypes of Huayu 198,Yumai 49-198,Zhongmai 1,Xinong 979,Ping an 8 and Taixue 12 were selected as experimental materials.Under 5 nitrogen application levels(0,120,180,240,360 kg·hm-2),the nitrogen nutrition index model based on critical nitrogen concentration was used.The nitrogen profit and loss of different varieties under different nitrogen application treatments were analyzed,and the changes of population dynamics,dry matter accumulation,plant nitrogen concentration and yield of wheat under different nitrogen treatments were discussed.The purpose of this paper is to establish the optimal value system of aboveground and underground key indexes of wheat under the optimal nitrogen nutrition status,and to explore the feasibility of optimizing the topdressing model based on nitrogen nutrition index and establishing the nitrogen topdressing model based on the critical value of NDVI.The main results are as follows:1.Nitrogen profit and loss classification of different wheat genotypes.The nitrogen nutrition index model can be used to classify the nitrogen profit and loss of different nitrogen application treatments of different wheat genotypes.In production,wheat reached the optimal nitrogen nutrition status(NNI=1)when NNI was in the range of 0.95≤NNI≤1.05.except for N120 treatment of YM49-198 from 2017 to 2018,the N0 and N120 treatments of other varieties were NNI<1,and the N240 and N360 treatments of HY198,YM49-198,TX12,XN979 and N360 treatments of PA8H and ZM1H were NNI>1.The rest of the treatments were NNI=1,and the change trend was the same in two years.2.Effect of nitrogen profit and loss on the growth of Wheat.Wheat yield varied from year to year.When NNI=1 was used in 2017-2018,the yield of wheat reached the highest,which was not significantly different from that of NNI>1,but significantly higher than that of NNI<1.Compared with NNI<1,the yield of NNI=1 increased by 11.65%,the number of spikes increased by 16.13%,and the number of grains per spike increased by 7.75%.When NNI>1,the yield increased by 10.84%,the number of spikes increased by 20.71%,and the number of grains per spike increased by 6.15%.From 2018 to 2019,when NNI>1,the yield of wheat reached the highest,which was not significantly different from that of NNI=1,but significantly higher than that of NNI<1.Compared with NNI<1,the yield of NNI>1 increased by 39.81%,the number of spikes increased by 37.30%,and the number of grains per spike increased by 20.61%.When NNI=1,the yield increased by 35.50%,the number of spikes increased by 34.90%,and the number of grains per spike increased by 23.51%.Compared with NNI<1 and NNI>1,the increase of yield was the result of the increase of panicle number and grain number per ear.With the advance of the growth period,the wheat population increased at first and then decreased,and reached the highest in the green stage.The number of population increased significantly with the increase of NNI,and there was no significant change when NNI increased to 1,and then continued to increase the number of NNI,population.The dry matter accumulation of whole wheat plant gradually increased with the advance of growth stage,and the accumulation ratio was the highest at jointing-flowering stage,followed by flowering-mature stage,and NNI>1 was the highest.From the rejuvenation stage,the dry matter accumulation of NNI<1 was significantly lower than that of the other two treatments,and the dry matter accumulation of NNI>1 was significantly higher than that of NNI=1 from flowering to maturity.Wheat pre-anthesis transport increased with the increase of NNI,but there was no significant increase in NNI,pre-anthesis dry matter transport at NNI=1.The dry matter transfer rate before anthesis increased at first and then decreased with the increase of NNI,and reached the maximum in NNI=1.The amount of post-anthesis photosynthetic assimilation and the contribution rate of post-anthesis photosynthetic assimilates to grains decreased with the increase of NNI,and reached the maximum when NNI<1.The dry matter accumulation and distribution ratio of wheat organs at mature stage accorded with the law of grain>stem and sheath>spike axis+glume>leaf,and the dry weight of each organ increased with the increase of NNI at mature stage.The distribution ratio of stem and sheath in NNI<1 was significantly higher than that in the other two treatments.The highest distribution ratio of ear axis and glume was NNI>1,while the grain allocation ratio of NNI=1 was significantly higher than that of the other two nitrogen nutrition status.3.Effects of nitrogen profit and loss on nitrogen utilization in wheat.The nitrogen content of wheat whole plant decreased with the increase of growth period,and increased with the increase of NNI.The decreasing rate of nitrogen content reached the maximum from turning green to jointing stage.At the beginning of returning to green stage,the nitrogen content of plants with NNI<1 was significantly lower than that of the other two treatments.The nitrogen accumulation of the whole plant of wheat increased with the increase of growth period,and the rate of nitrogen accumulation reached the maximum from turning green to jointing stage.The dry matter accumulation of NNI<1 was significantly lower than that of the other two treatments at the returning green stage,and the dry matter accumulation of NNI>1 was significantly higher than that of NNI=1 from jointing stage to mature stage.With the increase of NNI,the amount of pre-anthesis nitrogen transport in wheat increased continuously,which reached the maximum when NNI>1,and the difference was significant compared with the other two treatments,but the transport ratio increased at first and then decreased,and reached the maximum at NNI=1.The contribution rate is consistent with the proportion of transshipment.Nitrogen uptake after anthesis increased with the increase of NNI,and the contribution rate of NNI>1 to grain was the highest,which was significantly higher than that of the other two treatments.The rules are the same in different years.At mature stage,the nitrogen distribution ratio of grain>spike axis+glume>leaf>stem and sheath was significantly lower than that of the other two treatments with NNI<1.In the proportion of nitrogen in leaves and spike axis+glume,NNI>1 was the highest,and NNI=1 was the highest in grain distribution.The accumulation of soil inorganic nitrogen decreased at first,then increased and then decreased with the increase of growth period.in each period,the content of soil inorganic nitrogen in the soil with NNI>1 reached the maximum,which was significantly higher than that of NNI=1,and significantly higher than that of NNI<1.The decreasing rate of soil inorganic nitrogen accumulation reached the maximum from turning green to jointing stage.The accumulation of soil inorganic nitrogen increased after topdressing at jointing stage and decreased from flowering to harvest.With the increase of NNI,wheat nitrogen absorption and use efficiency nitrogen partial productivity and harvest index showed a downward trend,except that there was no significant difference between harvest index and NNI=1,other than NNI<1 reached the highest,the difference reached a significant level compared with the other two treatments,too much nitrogen surplus will significantly reduce nitrogen absorption and use efficiency.4.Establishment of key Index system aboveground and Underground under optimal nitrogen Nutrition status.NNI=1 was the optimal nitrogen nutrition status of wheat,and the accumulation range of biomass at jointing stage was 8172.12-9638.46 kg·hm-2.Using the established relationship model,the population number under the optimal aboveground biomass was 955.67-969.72(104 hm-2),the plant nitrogen concentration was 2.15-2.21%,and the 0-30cm soil inorganic nitrogen accumulation was 70.6-78.8 kg·hm-2;The accumulation range of biomass at flowering stage was 13243.11-16305.93 kg·hm-2.Using the established relationship model,the population number under the optimum aboveground biomass was 617.03-606.87(104 hm-2),the plant nitrogen concentration was 1.78%-1.86%,and the 0-30cm soil inorganic nitrogen accumulation was 120.7-150.4 kg·hm-2.5.Establishment of nitrogen topdressing Model for WheatThe relationship between nitrogen nutrition index and topdressing nitrogen fertilizer was analyzed.From returning to green stage to flowering stage,the correlation coefficients of each regression equation were 0.69,0.69 and 0.74,respectively.The amount of fertilizer application can be calculated by the difference of NNI between the wheat in the fertilizer application area and the wheat in the non-fertilizer application area.There is a good linear correlation between plant nitrogen content and NDVI in different periods,so the topdressing model of NNINDVI and N based on NDVI can be established.From returning to green stage to flowering stage,the correlation coefficients of each regression equation are 0.55,0.46 and 0.46,respectively.Thus,it is more convenient to diagnose nutrition and give a topdressing scheme. |
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