Fertilizing Properties of Potassium Feldspar Altered Hydrothermally

The material obtained through hydrothermal alteration of K-feldspar rock in alkaline conditions is a potential source of soluble potassium (K), but agronomic testing is needed to verify its capacity to supply K to crops. A (NH4)(2)SO4-based bioassay was used to test the capacity of the material to supply K to tomato plants (Lycopersicon esculentum Mill.) growing in a mixture of silt loam, peat moss, and sand. Potassium chloride (KCl) and unaltered K-feldspar rock powder also were tested for comparison. The fresh weight and K composition of the plants increased as doses of KCl or hydrothermal material increased, but not with increases in K-feldspar rock. Development of stem lesions, which develop as symptoms of K deficiency in the presence of (NH4)(2)SO4, were eliminated by KCl or hydrothermal material but not by feldspar rock. A beneficial effect may occur due to the calcium (Ca) supplied or with adjustment of soil acidity by the hydrothermal material. The hydrothermal material is a K fertilizer at least as effective as KCl since it yields the same or better plant weight.