Application and Modification of Recommended Nitrogen Application Model for SPAD Value of Cotton

【Objective】 The purpose of the thesis is to provide scientific basis for the accuracy, universality and rationality of applying cotton SPAD method recommended fertilization model. 【Methods】 This thesis establishes three treatments through field plot experiment: Determine recommended nitrogen application (N₁) based on the SPAD value of cotton growth period; Determine recommended nitrogen application (N₂) in line with the SPAD value of cotton leaf age (N₂); Carry out recommended nitrogen application (N₃) by following the local high yield model.The recommended nitrogen application model of SPAD value is modified through observing and comparing the variation features of SPAD value, yield composition index and so on. 【Results】 It is y=0.090,3x+46.618, R²=0.855 for the correlation between N₁ treatment and SPAD value; and is y=0.108,6x+48.666, R²=0.765 for the correlation between N₂ treatment and SPAD value, in which the correlation between nitrogen recovery and SPAD value of N₁ treatment was higher than that of N₂ treatment. No significant difference in the effect of nitrogen recovery amount on yield between the treatment of N₁ recommended by M₁ and the treatment of N₂ recommended by M₂; The nitrogen recovery amount 417.45 kg/hm² of of N₁ is higher than local high-yield nitrogen recovery amount, and the 285.40 kg/hm² of N₂ is lower than the local high-yield nitrogen recovery amount, while the yield of N₁ and N₂ is obviously lower than that of local high yield. During each growth period of cotton, the trend of topdressing of N₁ and N₂ is basically consistent with that of cotton, while the topdressing of N₁ is higher than that of N₂ in each period. 【Conclusion】 It is scientific and applicable for the recommended nitrogen application model of cotton SPAD value, while it needs to modify the model parameters at the change of soil, climate and management mod to reach the maximum correlation between SPAD value and nitrogen application amount. It is able to quickly obtain the new formula of recommended fertilization that can be used in the current year by reverse deduction when modifying recommended nitrogen application model of SPAD value though the use of the recommended fertilization amount of the original model and the local high yield fertilization amount with many years.