Study On Nitrogen Fertilizer Spectral Diagnosis Precision Nitrogen Fertilization Model In Northeast Spring Maize

Maize production maintains national food security,and nitrogen has a significant effect on the increase in corn production and quality improvement.Human-diagnosed crop nitrogen nutrition status cannot be quantified,indoor analysis of a large number of crop samples for nitrogen analysis has poor timeliness,and the use of Green Seeker spectrometer to obtain crop information is fast and non-destructive,Therefore,this method has been widely applied in the field of nitrogen nutrition diagnosis and fertilization recommendation.Based on the background of extensive maize planting area and low nitrogen utilization rate in Northeast China,this paper draws on the optimal fertilization algorithm（N fertilization optimization algorithm,NFOA）for crop canopy NDVI and nitrogen fertilizer application by Raun et al.And introduces new agronomy parameters（maize variety growth period,nitrogen free region corn yield,etc.）.And considering the amount of N absorbed by corn and the change of nitrogen utilization rate,the field experiment and indoor analysis were combined to test the canopy normalized vegetation index（NDVI）and the nitrogen nutrition status at the top of the Maize Jointing Stage under different nitrogen application levels.The purpose of this study was to study the correlation between NDVI,nitrogen content and yield of maize after jointing new agronomic parameters,so as to provide a theoretical basis for reconstructing the optimal fertilization algorithm model（NFOA）and apply it to corn fertilization decision-making.In order to achieve corn nondestructive diagnosis and precise and variable recommended fertilization,and further improve the economic and environmental benefits of maize production.This article has the following research results:（1）Based on the correlation analysis between NDVI value and corn yield,the yield of maize was positively correlated with the NDVI value.When the NDVI value reached the maximum of 0.82,the corn yielded the highest yield of 12.86 t/hm^2.The correlation coefficient between NDVI value and yield of maize was 0.87（P<0.05）,reaching a significant level.（2）Under basal and topdressing treatments,the maximum accumulation of total nitrogen in the above-ground biomass and grain of mature maize was achieved at the highest nitrogen application level of N4,both of which increased with the increase of nitrogen fertilizer application rate,and the top dressing treatment was higher than that of base fertilizer.In treatment,the total nitrogen content in the above-ground part of maize increased by 11.39%,and the total nitrogen content in maize grain increased by 4.61%.The total nitrogen content in maize grain was generally higher than that in the above-ground part of the crop,indicating that the plant nitrogen was transferred to the growth period of maize and mostly transferred to Grain for improving corn quality.（3）Applying nitrogenous fertilizer can increase corn yield,and the base fertilizer treatment yields 3.55%to 14.17%higher yield than that of the non-nitrogen treated area.The topdressing treatment increases the yield by 8.06%to 19.15%compared with the non-nitrogen treatment,and the topdressing treatment is better than the base fertilizer treatment.Corn production increased by 4.36%to 5.36%.The amount of nitrogen-based fertilizer had no significant effect on agronomic efficiency.The average agronomic efficiency of base fertilizer was 21.56 kg/kg.The agronomic efficiency of base fertilizer under different N treatments was generally higher than that of topdressing fertilizer.This experiment was applied to N1treatment.The highest agronomic efficiency was 14.01 kg/kg.（4）By using the field trial data of 2016 to analyze the original NFOA model,the potential maize yield YP0 in the original model did not consider the impact of the growth period of the maize variety on the NDVI change rate,and the nitrogen fertilization amount calculated in the current season based on the original model was due to No consideration was given to subtracting the amount of soil nitrogen absorbed by corn,resulting in a calculated value of nitrogen fertilizer is much higher than the actual production required.Therefore,in order to estimate the amount of top dressing according to the top-dressing model more in line with the actual production,the proposed model predicts the potential yield of corn in the original model.The model and the seasonal nitrogen fertilization quantum model were rebuilt.（5）In the actual production process,the amount of nitrogen absorbed by maize and the rate of topdressing are unknown before corn is topdressing.This experiment has a certain correlation between the amount of soil nitrogen absorbed by maize and the ratio of topdressing and the potential yield of corn.Based on the data from the field trials in 2016,two relationships were preliminarily established:The correlation equation for the ratio of absorbed nitrogen to total nitrogen（y,%）and potential yield（x,t/hm²）of maize after top dressing is:y=18.476x²-438.72x+2661.6,equation correlation coefficient r=0.96（p<0.05）.The correlation equation between top dressing utilization（y,%）and potential yield（x,t/hm²）is:y=-16.283x²+355.74x-1871.2,and the equation correlation coefficient is r=0.70（p<0.05）.（6）Through the introduction of agronomic parameters such as maize growth period and nitrogen-free maize yield,re-analyze the correlation between NDVI and maize nitrogen nutrient diagnostic indicators,and use it to reconstruct the sub-model for predicting potential maize yield in the original NFOA model.The applied model of the reconstructed submodel was YP0=9.7185+1E-05e^{6.7206INSEY’},and the correlation coefficient r was 0.86（p<0.05）.Considering the amount of soil nitrogen absorbed by maize and the utilization rate of nitrogen fertilizer will be changed due to soil fertility,In order to reconstruct the original nitrogen fertilizer fertilizer quantum model in the original NFOA model,the rebuilt submodel application equation is FNR=（GNUP-FNUP）*（1-SN/PTN）/ZFU,where SN/PTN represents the corn planting community after top dressing SN accounts for the percentage of PTN.ZFU indicates the utilization ratio of planting plots.And through a 2017 independent test model validation.Using the NDVI values obtained during the jointing stage of the two varieties of maize in 2017,a preliminary test was conducted.There was no significant difference in the amount of fertilizer applied in the season between the two varieties of corn based on NDVI values at different periods before top dressing and the NFOA model.The actual production error is within 5%,which indicates that the reconstructed NFOA model can be applied to the diagnosis of spectral nitrogen nutrition in maize and nitrogen fertilization with precise variables.