SPAD Values Based Nitrogen Nutrition Diagnosis And Regulation In Rice

Nitrogen(N)is one of the most important limiting factors for crop production.Optimal N management is crucial for high-efficient crop production and sustainable agriculture,and also for the reduction of N fertilizer's negative effects.In our study,rice was taken as the research object.Portablel SPAD meter was used to investigate three topics.They are "Systematic analyses for SPAD meter measurement in rice","SPAD values based nitrogen nutrition diagnosis in rice" and "SPAD values based nitrogen regulation in rice".In addition,field experiments were undertaken to examine the performance of the newly developed N regulation methods.Based on these exploration,systematic calibration methodology was developed for SPAD meter measurement in rice,and critical N management period was defined for potential N regulation in rice as well.In the meanwhile,SPAD values based N regulation method was extended in our study,and the newly developed approaches can provide the key technical support for making proper decision on topdressing of N fertilizer in crops production.Field experiments were conducted with different N application rates in the mainly planted rice varieties in Jiangsu province of east China.Firstly,optimal leaf positions for SPAD meter measurement in rice were studied.A flatbed color scanner was introduced to estimate the dynamic chlorophyll concentration along the leaf blade as well as the irregular shapes of leaves.Furthermore,calculus algorithm was adopted to determine the most representative positon for chlorophyll measurement.The results showed that the 2/3 positon from leaf base can accurately represent the N nutrition of the specific leaf,which can also produce a low measurement variance simultaneously.In addition,extracted chlorophyll(Chla+b)and leaf N concentration were compared with di-positional SPAD values,2/3 position of lower leaves tended to be more sensitive to the N deficiency.Thus,the most suitable positon for SPAD meter measurement is the 2/3 positon of the fourth fully expanded leaf from fop.Based on the SPAD meter measurement analysis in rice,SPAD values based N nutrition diagnosis was further explored.During the vegetative period,di-positional SPAD values and indices were related to four N indicators,including leaf N concentration(LNC),plant N concentration(PNC),plant N accumulation(NA)and N nutrition index(NNI).And then,proper N diagnosis models were developed.The results showed that,the normalized SPAD index of the fourth fully expanded leaf(NSI4)tended to be more sensitive to the N deficiency of plants.Meanwhile,the normalized method was also promising to diminish the influence of different experimental sites and varieties.During the critical N management period(from stem elongation to booting stage),two stable interphase N diagnosis models were selected(Model 1:NA=0.0279e8.6957NS14,R2=0.730**,n=45;Model 2:NNI=0.0163 e4.13NS14,R2 = 0.767**,n = 45,NSI=0.80-1.00),and they were also calibrated with independent data.These results can provide a reference for diagnosing the N status during the stem elongation and booting stages in rice.Depending on the SPAD values based N diagnosis research,attempts were made to integrate SPAD values with two N regulation approaches,called N fertilizer optimization algorism(NFOA)and N nutrition index(NNI)respectively,and SPAD values based NFOA and NNI topdressing strategies were then established.With historical data,the corresponding equation parameters were calibrated,and only one variable,namely NSI4(normalized SPAD index of the fourth fully expanded leaf from fop),was included in the two newly modified N topdressing approaches.Through the in-field verification,SPAD values based NFOA and NNI approaches are applicable under different N conditions,including light N deficiency as well as suitable and luxury N conditions.In the meanwhile,N agronomy efficiency(AE),N use efficiency(NUE),partial factor production(PFP)and grain production efficiency(GPE)were calculated under different N management strategies,and the SPAD values based N regulation treatments performed well in these indexes.