NDVI, SPAD, and Petiole Sap Nitrate in Nitrogen Nutrition and Growth Assessment and Yield Prediction for Cotton

Little information is available on the comparison of canopy normalized difference vegetation index (NDVI) and SPAD reading with petiole sap NO₃^-‒N concentration in assessing N nutrition and growth and predicting yield for cotton. Treatments of four N rates (0, 34, 67, and 101 kg N ha^-1) under two cover crops (no cover and hairy vetch) with four replications from a 33-year long-term field trial were used to evaluate canopy NDVI and SPAD-502 reading against the conventional petiole sap NO₃^-‒N concentration in assessing N nutrition and growth and predicting yield for cotton. Although these three parameters all increased as the N rate was enhanced, NDVI and SPAD reading responded less sensitively to N rates. Canopy NDVI and SPAD reading varied less with the growth stage than petiole sap NO₃^-‒N. Out of the three parameters, petiole sap NO₃^-‒N concentration was more appropriate at early square but SPAD reading was more suitable during early bloom to late bloom in assessing cotton N nutrition status. The SPAD reading was a better parameter for estimating cotton growth than NDVI and petiole sap NO₃^-‒N. Canopy NDVI was more appropriate than SPAD reading and petiole sap NO₃^-‒N at early square while SPAD reading was better than NDVI and petiole sap NO₃^-‒N during early bloom to late bloom in cotton yield prediction. Overall, the benefits are not consistent in using NDVI or SPAD reading to assess plant N nutrition and growth and predict lint yield for cotton compared with the conventional utilization of petiole sap NO₃^-‒N concentration.