| CPC G01N 33/0098 (2013.01) [G01N 21/55 (2013.01)] | 10 Claims |

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1. A diagnostic method for drip irrigation cotton with nitrogen nutrient deficit, wherein the diagnostic method comprises the following steps: determining sensitive leaf layer of cotton according to the growth stage of cotton; collecting spectral reflectance and biomass of each functional leaf in the sensitive leaf layer, calculating average spectral reflectance of the sensitive leaf layer and maximum leaf biomass; calculating optimized spectral index value according to the average spectral reflectance, calculating nitrogen concentration according to the optimized spectral index value; calculating critical nitrogen concentration according to the maximum leaf biomass; calculating nitrogen nutrition index of the cotton according to the nitrogen concentration and the critical nitrogen concentration, using the nitrogen nutrition index to characterize the abundance and deficiency of nitrogen nutrition in the cotton.
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