Study On Suitable Nitrogen Indices Dynamic Models And Nitrogen Fertilizer Regulation Of Winter Wheat In Wheat-rice Cropping Area

Nitrogen(N)is the nutrient that most often limits crop production.The intensification of crop production has been accompanied by decreased N use efficiency.Judicious use of N fertilizer is essential for increasing the economic return for crop production and minimizing potentially negative effects on environment.The N status diagnosis and accurate management is an integral part of precision agriculture.Multi-locational field experiments with varied N application rates using four winter wheat cultivars as experiment material were carried out in different years.This study was conducted to analyse the dynamic variation in characteristic of canopy spectral vegetation index and critical nitrogen concentration in winter wheat.The plant critical N concentration,N nutrition index and canopy spectral index models were constructed for N nutrition diagnosis and management in winter wheat to develop effective diagnostic tool and theoretical basis.Firstly,this study was aimed to couple modern remote sensing based spectral index with agronomic indicators for monitoring crop growth and development.The critical N dilution curve in winter wheat was established according to the methodology proposed by Justes.The curve can be described by equation,Nc%=4.29DM-0.425,R2=0.92.Comparison of the critical N dilution curve developed in present study and that developed for winter wheat in North China Plain indicated that a same critical N dilution curve can be used in-season N diagnosis in different climatic conditions.The N nutrition index model was then constructed on the basis of critical N dilution curve,the results showed that the values nitrogen nutrition index were greater than 1 and lower than 1 under non-limiting and limiting N conditions,while the value of nitrogen nutrition index under appropriate nitrogen nutrition was around 1.Then,a linear quadratic relationship between RY and NNI was observed in winter wheat cultivars after normalization.The quadratic relationships at jointing stage can be described by equations,RY=1.12NNI-0.08(NNI<0.95)and RY=0.98(NNI?0.95),while at booting stage these relationships can be described by equations RY=0.96NNI+0.05(NNI<0.98)and RY=0.99(NNI?0.98).Our results revealed that the NNI=0.95 at jointing and NNI=0.98 at booting stages indicated the optimum N status in winter.Setting the yield target on the basis of quadratic relationship between RY and NNI,prior to N corrective decision making will result in reduction in N fertilizer application rate and minimize environmental hazards.The quantification of N fertilizer application can be calculated according to the principle of nutrient balance.This nitrogen management strategy is mainly suitable for the regions with the known records of past fertilizer application.The N requirement estimated in present study was close to that used in past.Thus,the present N management strategy is appropriate for the region where it was developed.To minimize the influence of nitrogen and variety,the NDVI of a treatment was normalized by the maximal NDVI to develop the Logistic model between RNDVI and RAGDD.This model can be described by equation,RNDVI=1.02/(1+e^(-11.62(RAGDD-0.25))).Then,an optimal NDVI dynamic model in wheat canopy during vegetative(before flowering)growth of winter wheat was constructed by using RNDVI times NDVImax obtained from experience in the target yield.Lastly,the NDVI based nitrogen management model on was proposed using the optimal NDVI dynamic model for winter wheat before flowering.The NDVI was divided into three groups at jointing stage<0.65,0.70?0.65,>0.70 and booting stage<0.75,0.75?0.85,>0.85,respectively on the basis of allometric growth relationships.Then the relationship between ?NDVI and ?N was simulated for each group.The difference value between practical NDVI and ONDVI under a target yield can be used for quantification of N requirement by checking the box map between ?NDVI and AN.The total N requirement estimated in present study was close to that used in past.Thus,the present N management strategy can be used as reference value in nitrogen management.