Diagnosis Of Nitrogen Nutrition In Pepper Based On SPAD And NNI

Nitrogen is an important nutritional factor to promote the growth and yield of pepper.At present,some farmers still believe that the amount of nitrogen fertilizer is proportional to the crop yield,and they fail to apply nitrogen scientifically according to the actual absorption capacity of crops,leading to the widespread over application of nitrogen.Rational application of nitrogen can not only ensure the normal growth and development of plants,but also improve the utilization efficiency of nitrogen fertilizer,thus reducing production costs and reducing environmental problems such as secondary salinization.Studies on different crops showed that the contents of SPAD,chlorophyll and nitrogen were closely related.Therefore,SPAD can be used to quickly determine nitrogen status in crops.In this paper,a critical Nitrogen dilution curve was established by analyzing the SPAD value,chlorophyll content,biomass,Nitrogen content,Nitrogen accumulation and yield of red Dragon no.23 pepper under different Nitrogen treatments,and the Nitrogen trophic index was analyzed.The relationship between（nitrogen nutrition index,NNI）and the above indexes;By PLS method analyzes the SPAD value and nitrogen related indicators,to explore pigment pepper nitrogen diagnosis of SPAD in sensitive layer leaves and leaf,and based on this leaf SPAD values of constructing NNI of mathematical relation model,and the model of accuracy analysis,model can meet the demands of nitrogen diagnosis accuracy,and used to diagnose chili nitrogen conditions.The main results are as follows:1.According to the changes of above-ground biomass,leaf biomass and corresponding nitrogen concentration of pepper,the critical dilution curve of nitrogen concentration of pepper under different nitrogen application levels was constructed.The critical dilution curve of above-ground nitrogen concentration of pepper’Honglong 23’was Nc=4.177W^-0.25（R2=0.95）.The dilution curves of leaf,upper leaf and middle leaf were Nc=4.308W^-0.879（R2=0.87）,Nc=2.452W^-0.99（R2=0.94）,2.134W^-0.585（R2=0.61）,respectively.The dilution curve of lower leaf was Nc=1.385W^-0.647（R2=0.60）.According to the correlation coefficient,it is more scientific to determine the nitrogen concentration dilution curve constructed by the upper leaf.In the whole growth period of pigment,the NNI ranges from 0.64 to 1.00 in aboves and 0.48 to1.00 in upper leaves.2.With the advance of growth period,SPAD value and chlorophyll content of pepper increased firstly and then decreased.Except the fruit maturity stage,the biomass and nitrogen content in all growth stages increased with the increase of nitrogen application level,and the biomass and nitrogen content in all growth stages were higher with 20%nitrogen reduction,indicating that 80%nitrogen can guarantee the normal growth and development of pepper.3.SPAD was closely related to nitrogen abundance and deficiency in pepper,and could be used as an index for rapid diagnosis of nitrogen.Using quantitative analysis method of PLS model,taking SPAD,chlorophyll,nitrogen content,nitrogen accumulation and other indexes as parameters,the central position（C）of the upper leaf（UL）of pigment pepper was determined to be sensitive to nitrogen abundance and deficiency through projection value of importance of index variable（VIP）,and its SPAD value could better reflect nitrogen nutritional status.As the preferred sampling site for SPAD diagnosis of nitrogen.4.There is a linear quadratic regression relationship between THE SPAD value of the middle position of the upper leaf of pepper and NNI,and the correlation is high.Therefore,the SPAD value of the middle position of the upper leaf of pepper can be used to judge and evaluate the nitrogen nutrition level of pepper plants,which lays a foundation for the realization of fast,low-cost and real-time diagnosis,rational fertilization and guidance of topdressing.