Nitrogen Nutrition Diagnosis And Variable Rate Fertilization Of Wheat Based On Near Ground Multispectral Images

China is a country with a large population,so food production plays an important role in agricultural production and social development.Wheat is one of the most important food products in China.The Chinese people’s consumption of wheat accounts for about a third of the national consumption level,and the demand for wheat is in the second place in the country.This indicates that the quality of wheat and its yield can greatly affect the improvement of people’s living standard,the growth of national economy and the guarantee of food security.Therefore,according to the diagnosis of nitrogen nutrition during the wheat planting process,it can better coordinate and meet the demand of wheat for different nutrients,and finally achieve the goal of high quality and high yield.The traditional nutritional diagnosis method of wheat is to obtain the nitrogen content by chemical analysis of the wheat plant samples.According to this to determine the abundance of nitrogen nutrients in the wheat plant body.But this method is time-consuming,laborious,and it has a certain damage to the crops.In addition,China’s demand for wheat is increasing,which requires us to find ways to increase wheat yields quickly.Fertilization is an important measure to increase crop yield per unit area.,But due to the unreasonable use of fertilizer application in China for a long time,resulted in a series of serious consequences of changing in soil acidity,aggravating in soil pollution,nutritional imbalance,and weaken the crops production capacity which go against agricultural production and economic development.Therefore,scientific and reasonable fertilization through wheat nutrition diagnosis is an important way to promote the sustainable development of wheat production.The study area of this research is Shandong Agricultural University experimental field.According to combining with the status of nitrogen nutrition diagnosis and fertilization at home and abroad,using the ADC portable multispectral camera and SPAD-502 chlorophyll meter to obtain the field data to diagnose the nitrogen nutrition of wheat,explore the method of nitrogen content estimation of wheat based on near ground multispectral data,make variable rate fertilization decisions.It provides a fast and effective technical method for wheat nitrogen content estimation,nutrition diagnosis,and variable rate fertilization.It is of great significance for rational fertilization,effective fertilization,and reducing the pressure on environment caused by the use of fertilizers.First of all,I used the measured wheat canopy SPAD value of over-wintering stage,green returned stage and standing stage,total nitrogen content of wheat plant and soil available nitrogen content to do correlation and regression analysis with NDVI which obtained from near ground multispectral data,establish a variety ofestimation models of wheat chlorophyll,total nitrogen content of wheat plant,and soil available nitrogen content,the optimal estimation model is determined and the ideal result is obtained through further preferential selection and verification.Then,the nitrogen fertility status of the wheat field was graded according to the comprehensive spatial distribution analysis of the total nitrogen content of wheat plants above the ground and the soil available nitrogen content in the underground part of the wheat field.Finally,the nitrogen fertilizer application model was optimized according to the total nitrogen content of wheat plant and the soil available nitrogen content in the underground part of the wheat field.（1）Constructed five kinds of estimation models of wheat chlorophyll,total nitrogen content of wheat plant,and soil available nitrogen content by regression analysis method.Determined the optimum estimate models of wheat chlorophyll content in over-wintering stage,green returned stage,standing stage,and the optimum estimate models of total nitrogen content of wheat plant,soil available nitrogen content which have the advantages of fast,accurate,and field non-destructive.The optimum models are y=8.643ln（x）+68.756,y=73.277x^0.232,y=28.939e^0.884x,y=11.127x^2.1534,y=243.935ln（x）-942.806,respectively.（2）The nitrogen fertilizer of wheat field was divided into five levels of extremely lack,lack,medium,rich and extremely rich according to the comprehensive spatial distribution analysis of the total nitrogen content of wheat plants above the ground and the soil available nitrogen content in the underground part of the wheat field using the method of the Inverse Distance Weighted in GIS spatial analysis.It was found that when the soil available nitrogen content at the sampling point was lack,the total nitrogen content of wheat plant at the sampling point was relatively lack,and vice versa;The total nitrogen content of wheat was increased with the passage of time and increased along with the increase of soil available nitrogen content in wheat field;The total nitrogen content of wheat plant changed little from over-wintering stage to green returned stage,the total nitrogen content of wheat plant changed significantly at the standing stage,this was because the nitrogen fertilizer consumption of green returned stage had delayed effect,and the soil available nitrogen content was relatively higher when the standing stage was coming.（3）Referencing to the existing nitrogen fertilizer application model,a new nitrogen fertilizer application model was optimized according to the actual situation of the research area:Z=0.5×(32-11.127X₁^2.1534×10)-2.462E-009X₂^5.807×10^-3.It will assist in reaching the goal of saving fertilizer cost,producing high yield,and protecting environmental according to the proposed nitrogen fertilizer application model accurately calculate the reasonable amount of nitrogen fertilizer which should be applied based on the expected output.