Effects Of Different Nitrogen And Phosphorus Application Rate On Yield,Nutrient Uptake And Utilization Of Summer Maize

The rational combination of N and P is the main way to improve nutrient use efficiency and yield.This study is based on the grain fields with different soil fertility levels that have been implemented under the wheat-maize double-cropping system in Guanzhong since 2009.The field experiment was set up with 4 phosphorus application levels（indicated as P0,P1,P2 and P3）at 0,60,120,180 kg·hm^-2,and 5 nitrogen application levels at 0,75,150,225,300 kg·hm^-2 level（represented by N0,N1,N2,N3 and N4）,the tested maize varieties were Zhengdan 958 and Yuyu 22.The growth dynamics of summer maize plants were monitored to study their yield,plant nitrogen,phosphorus and potassium nutrient uptake and utilization,soil water dynamics,and water and fertilizer use efficiency,on this basis,a critical nitrogen concentration dilution curve model was constructed in 2019 and 2020.The main research results as follows:（1）Combined application of N and P was beneficial to improve the agronomic traits of summer maize,and the difference between the two varieties was not significant.The effect of P application was better at the level of P2.Under the same P application level,the overall plant height was N3>N2≈N4>N1>N0,and the stem diameter was N4>N3>N2>N1>N0among different N application rates.Combined application of N and P could maintain green leaf area and delay plant senescence.P fertilization increased leaf SPAD,LAI and the dry matter accumulation of summer maize in each growth period by promoting N uptake and utilization by plants,and the P application effect was P2≈P3>P1>P0.The overall N application effect was N3>N4>N2>N1>N0 under the same P application level.（2）From jointing to tasseling stage,maize stems and leaves were the main organs for N,P and K absorption.The accumulation of N and P in leaves was higher than that in stems,and the accumulation of K in stems was higher than that in leaves.The accumulation of N,P and K in the ear of maize increased,the proportion of N and P accumulation in the grain was the highest,and the K accumulation was mainly in the stem after the tasseling stage.The distribution ratio of N and P in each part of the plant at the mature stage is grain>leaf>stem>cob>bract.The distribution ratio of N and P in the ear would increase under the good water and heat conditions,on the contrary,the accumulation and distribution of N and P would increase in the stem and leaves of the vegetative organs.There were differences in the distribution ratio of K between the two cultivars.Zhengdan 958 was stem>leaf>grain>bracts>cob,and Yuyu 22 was stem>grain>leaf>cob≈bract.Combined application of N and P could improve the absorption and accumulation of N,P and K in grains,and the transport of N,P and stem K from stems and leaves to grains,which was conducive to the accumulation of more N,P and K nutrients in grains,of which N3P2 level,the accumulation of N,P and K in plants could be maintained at a relatively high level.（3）Phosphorus fertilization increased the yield by increasing the number of corn ears,and the effect of P2 treatment was the best.Yield and its components showed an increasing trend with the increase of N application level.The number of grains per ear and 1000-grain weight obtained the highest values under N application N3 and N2 levels,respectively.It could significantly increase the total output value and net output value of summer maize,and could obtain a higher production-to-investment ratio.The two-year yield-effect equation fitted the optimum N application rate of 212-215 kg·hm^-2,P application rate of 109-110kg·hm^-2,and the highest summer maize yield was 8362-10121 kg·hm^-2.（4）Construct and verify the critical N concentration dilution curve model of summer maize based on shoot biomass under four P application levels(P0,N_c=27.98DM^-0.249;P1,N_c=29.77DM^-0.182;P2,N_c=30.81DM^-0.138;P3,N_c=30.06DM^-0.187),the n-RMSE of the model were 10.23%,6.67%,6.95%and 7.19%,respectively,with good stability.Appropriate application of N and P could improve the nitrogen tolerance of plants and reduce the rate of N dilution.The nitrogen nutrition index model（NNI）constructed based on the critical N dilution curve model was reliable in diagnosing the N nutrition status of maize plants during the critical growth period,N2-N3 and P1-P2 were the best conditions,and these treatments resulted in maximum above-ground biomass and yield.Based on the fitting curve of comprehensive N application rate and grain yield,the N rate of 188-214 kg·hm^-2 and P rate of 60-120 kg·hm^-2 was the optimal fertilization option for summer maize in Guanzhong Plain,Shaanxi.（5）P application was beneficial to promote the absorption and utilization of soil water by the roots of summer maize in the early and middle stages of growth.N application expanded the soil space for roots to absorb water,and the absorption capacity of soil water increased with the increase of nitrogen application rate.N fertilization enhanced the utilization of deep soil water by plant roots in the later stage of growth,and the maize roots under N2 and N3 levels had better effects on soil water utilization.P application was beneficial to enhance the water use efficiency（WUE）of summer maize,which was P3>P1>P2>P0,and the overall effect of N application was N3>N2≈N4>N1>N0.The nitrogen and phosphorus fertilizer agronomic efficiency（NAE,PAE）of summer maize showed a decreasing trend with the increase of P and N application levels.N1P0and N1P3treatments were beneficial to ensure higher NAE,and N2,N3 level had higher PAE.The partial productivity of nitrogen and phosphorus fertilizers（NPFP,PPFP）decreased with the increase of N and P application rates,respectively,and the combined application of N and P was beneficial to improve NPFP and PPFP.