Use of Sorption‐Isotherms for Evaluating Potassium Requirements of Plants

Abstract

Abstract A sorption‐isotherm technique was used to evaluate plant‐available K for potatoes ( Solanum tuberosum var. ‘Russet Burbank’), celery ( Apium graveolens ‘Utah Pascal No. 15’), tomatoes ( Lycopersicon esculentum var. ‘Owyhee’) and beans ( Phaseolus lunatus var. ‘Fordhook’) in a greenhouse study. Sorption equilibrium was reached after 24 hours. Desorption equilibrium was reached after 1 hour. A 95% yield of beans, tomatoes, celery, and potatoes was achieved with 7.2, 7.4, 11.1, and 13.6 µg/ml K in sorption‐equilibrium solution and 2.6, 2.7, 3.5, and 4.7 µg/ml K in desorption‐equilibrium solution, respectively. The energies of exchange, E k , for these sorption equilibrium solution K levels were −2,500, −2,485, −2,360, and −2,300 calories/M, respectively. Increase in the equilibrium‐K levels beyond the level needed for 95% yield resulted in little or no change in the growth of these crops. The desorption‐equilibrium solution K levels for maximum yields in this study are in close agreement with the solution K levels of nutrient‐culture studies reported earlier. Tissue‐K concentrations for 95% yield were 1.78, 3.30, 3.60, and 4.65% in beans, celery, potatoes, and tomatoes, respectively. Potential use of this technique for determination of K requirement is discussed.