RELATIONSHIP BETWEEN TOTAL AND EXTRACTABLE COTTON LEAF POTASSIUM IN STUDIES INVOLVING SOIL AND FOLIAR-APPLIED TREATMENTS

Information on the potassium (K) concentration of cotton leaves is use ful to researchers, consultants, and producers for evaluating possible nutrient deficiencies and subsequent need for fertilizer applications . Procedures for evaluating leaf K concentrations generally involve di gestion techniques requiring considerable time per sample. Extraction procedures require less time per sample for evaluating nutrient concen trations. An extraction method needs to be correlated with digestion d ata to evaluate accuracy of the procedure. This study was initiated to evaluate total leaf K, as detected by the sulfuric acid (H2SO4)-hydro gen peroxide (H2O2) method, and extractable leaf K, using 2% acetic ac id, in selected leaf materials representing a wide range of soil-extra ctable K, foliar treatments, and growing conditions. Cotton leaves pre viously collected from other experiments with known total K concentrat ions were extracted with 2% acetic acid. Regression analyses were cond ucted evaluating digestible and extractable K by sample dates within s pray periods. Regression analyses were continued evaluating data by sp ray periods, soils, soils by year, and all sites. Extractable leaf K i ncreased linearly with digestible K for leaf materials collected withi n each spray period from the 1991, 1992, and 1993 surfactant tests. Th e equation for samples collected one day after the first foliar K spra y was: Extractable K (EK) = 0.0877 + 0.8774 Total K (TK) having an R(2 ) of 0.94 for the 30 samples. Combining sampling dates within spray pe riods showed the relationship between total and extractable leaf K rem ained high. The regression equation for the 1,942 leaf comparisons (ac ross soils, years, and treatments) was: EK = 0.0823 + 0.9204 TK having an R(2) of 0.94. Extractable leaf K as estimated by the 2% acetic aci d extractant provided an excellent estimate of total leaf K as determi ned by H2SO4-H2O2 digestion.