The Plant Availability of Potassium in Fly Ash

The availability of K in fly ash obtained from nine coal burning power generating plants was evaluated by greenhouse and laboratory procedures. The total K content of the samples of fly ash ranged from 0.65 to 3.14%. Eight of the samples were bituminous coal ashes, and one was lignite coal ash. The samples of bituminous coal fly ash neutralized less than 0.25 meq H 3 O + /g, whereas the sample of lignite coal fly ash neutralized 3.05 meq H 3 O + /g. Application of three samples of the bituminous coal fly ash and the sample of lignite coal fly ash increased K uptake by corn plants ( Zea mays L.) grown on Davidson clay loam. Potassium uptake was higher from application of 158 mg K as KCl to 2,100 g of the soil than from application of a higher rate of K as the four samples of fly ash. Equivalent K uptake by corn plants occurred from application of 79 mg K as KCl and 207 mg K as the lignite fly ash. However, yield was lower where the ash was applied. Tissue analyses indicated that B toxicity limited yield on the latter treatment. Application of certain of the fly ash samples increased Mg uptake by corn plants. This increase in Mg uptake probably caused a decrease in K uptake by plants grown in the fly ash‐soil mixtures.