Study On Chlorophyll Meter Application On Nitrogen Nutritional Diagnosis For Cotton Plants

Object: This paper was proposed to study using SPAD for cotton plant N nutrition diagnosis.Leves order and leaves position were determined for cotton plant N diagnosis. Study the effects of different nitrogen treatments and cotton varieties on SPAD value. To establish cotton nitrogen diagnosis model based on SPAD value and validate the model.Methods: Pot and field experiment were conducted to establish a model based on SPAD measurement and cotton plant N–related physiological factors.And established models was validated by field demonstration.Conclusion:1. The results showed that leaf nitrogen content and SPAD value varied markedly in different leaf order. Therefore, in order to take reliable data for cotton plant N diagnosis by using SPAD, to select a fixed leaf order is necessary for the measurement. Our research indicated that the reverse 4th leaf from the apex of the main stem and position 2 is the best position for cotton plant.2. At the same N fertilization treatment, Xinluzao 13,Xinluzao 19 and Xinluzao 24′s SPAD value have the same trend during the whole growth stage. The minimum value appears the day after emergence 65 day, and the peak value appears the day after emergence 105 day. The SPAD value in cotton leaves was increased with increasing nitrogen fertilizer.The different of chlorophyll content is notable among varieties. Xinluzao13 and Xinluzao24′s SPAD value was much higher than Xinluzao19, Xinluzao13 and Xinluzao24 had no difference.3. Significant correlation was found between SPAD and leaf chlorophyll concentration, N concentration in leaf or N absorption per plant. There was a significant linear correlation between the SPAD value and the rate of applied nitrogenous fertilizer. A significant correlation between SPAD value and the cotton yield were found as well.The threshold SPAD value at budding peak stage, flowering stage, flowering peak stage and bolling stage were 60.5, 60.0, 60.8 and 59.1 respectively. Corresponding to the SPAD value change 1 unit in cotton plant, the quantities of applied nitrogenous fertilizer were assured. The validation results show that from seedling stage to bolling stage, 6 recommended fertilizing were conducted. The maximum fertilizing amounts at the day after emergence 75 day and 85 day.The threshold SPAD value of Xinluzao19 at the different cotton growth stages were56.2, 48.0, 48.5 and 50.7.4. In Xinluzao 13 and Xinluzao 24 ,optimized N treatment based on N diagnosis model reduce N application rate at 14.7% and 10.27%.During the vegetative growing period of cotton, without N deficiency symptom. At the same time, optimized N fertilization rate harvested higher yield or the highest yield than the Mid.N treatment.Plant dry matter, LAI and N uptake of cotton could be modeled by Logistic model, with high correlative coefficient.(r=0.8971～0.9990)...