Tissue Nutrient Concentration and Spectral Characteristics of Cotton K Deficiencies.

An effective, efficient method to determine K status in-season would give a producer the opportunity to correct yield-damaging deficiencies without making unnecessary fertilizer applications.  The objectives of this research were (1) to describe the spectral characteristics of cotton K deficiencies in the presence and absence of sufficient N, and (2) to determine if a plant tissue other than the leaf or petiole may be more indicative of cotton K status.  Field trials were conducted in 2012 at the University of Arkansas Experiment Stations in Fayetteville, AR and Marianna, AR.  Canopy reflectance was measured by a StellarNet  EPP2000 Spectrometer (StellarNet, Inc. Tampa, FL) within two hours of solar noon.  The most recently matured, fully expanded main-stem leaf and petiole four to five nodes from the apical meristem and uppermost white flower were harvested at the time of reflectance.  Tissue sampling and reflectance was measured at early flower and the second week of flowering.  Tissue samples were dried, ground, and sent to the Plant Diagnostic Laboratory for nutrient analysis.  Results are expected to show heightened sensitivity of the flower to K deficiency as compared to leaves or petioles and a strong correlation between flower K concentration and spectral response of K deficiencies.