The Study On Construction Of Critical Nitrogen Concentration Dilution Model And Rapid Diagnosis Based On Nitrogen Fertilizer Reduction Of Chrysanthemum Morifolimum(Ramat.)Tzvel.Chuju

There is a long history of Chrysanthemum morifolium（Ramat.）Tzvel.‘Chuju’planting,it is mainly produced in Chuzhou,Anhui Province.’Chuju’can be used as tea and medicine,it is the top of four medicinal chrysanthemums.Although the market demand for‘Chuju’is expanding,most farmers usually rely on experience to manage the application of nitrogen fertilizer and lack scientific and reasonable fertilization plans,resulting in low yield,quality,income and nitrogen utilization rate,which further hinders The development of industrialization.Based on field experiments in different years and nitrogen treatments,this study analyzed the variation of leaves,aboveground dry matter and nitrogen concentration,then researched on the relationship between the two factors,constructed a critical nitrogen concentration dilution model for different organs,and further establisheed the nitrogen nutrition index model（NNI）to diagnose nitrogen nutrition of‘Chuju’.At the same time,the study used SPAD value to determine the appropriate position of‘Chuju’leaves for diagnosing rapidly in the field,which provides a theoretical basis for accurate fertilization of‘Chuju’.The main results are as follows:1.The experiment used random block design and set five nitrogen levels,they are traditional nitrogen application（39.6 kg/mu）,nitrogen reduction by 15%（33.7 kg/mu）,nitrogen reduction by 30%（27.7 kg/mu）,nitrogen reduction by 45%（21.8 kg/mu）),non-nitrogen application（0 mu）.On the basis of the field test data of 2019-2020,the critical nitrogen concentration dilution model and nitrogen nutrition index model based on dry matter of‘Chuju’leaves（LDM）were constructed and verified.The results showed that the critical nitrogen concentration model was divided into two parts,When LDM﹤7.26g/plant,N_c=3.69%,LDM≥7.26g/plant,N_c=5.1685LDM^-0.17.The indicator of the validation model n-RMSE=11.77%,The stability of the model is good;A significant correlation was found between leaf nitrogen index（NNI）in different stages and flower yield.The flower yield is the highest and the NNI is the best in the nitrogen treament 420kg/hm²（30%nitrogen reduction）.2.The study used two years field experiment data to construct the critical nitrogen concentration dilution model and nitrogen nutrition index model（NNI）based on aboveground dry matter of‘Chuju’plant（PDM）.The results showed that the aboveground dry matter of‘Chuju’increased with the increase of nitrogen application within a certain range,then stabilized or decreased.The aboveground nitrogen concentration gradually decreased with the increase of dry matter.When PDM≥15.63g/plant,the two factors had a negative power function relationship,and the critical nitrogen concentration dilution model equation is:N_cnc=5.4353PDM^-0.206,R²=0.9003,PDM﹤15.63g/plant,the critical nitrogen concentration value is a constant 3.09%.Validation with independent experimental data showed that the model is sutiable;the established NNI model can better diagnose the nitrogen nutrition of’Chuju’,and the most appropriate nitrogen application is 420kg/hm²（30%nitrogen reduction）.The analysis between dried flower yield and aboveground dry matter,aboveground nitrogen concentration,NNI are all significantly correlated,which further showed that the model constructed in this study is reliable.3.The objective of the study was to find the appropriate leaf position for rapid diagnosis of nitrogen nutrition status of‘Chuju’by chlorophyll instrument（SPAD）in the field.The study analyzed changes in leaf SPAD values of the upper,middle and lower parts of‘Chuju’under different nitrogen levels and the relationship between SPAD values with yield to determine the appropriate leaf nitrogen diagnosis position.The results showed that the SPAD value of‘Chuju’leaves increased first and then decreased with the increase of planting days.SPAD values increased with the increase of nitrogen level.The difference between high nitrogen treatments was small.The upper and middle leaves were more sensitive to nitrogen levels,they are bothe significantly correlated with the leaf nitrogen concentration and yield.Combining the determination coefficients of the equations for different growth periods,the upper leaves can more accurately predict the leaf nitrogen content and yield changes.The suitable site for SPAD determination in this study is the upper leaves.