Potassium metaphosphate as a fertiliser for pastures

Abstract

Laboratory studies have shown wide variation in the ability of soils to retain potassium against leaching, the amount of applied K leached varying from 7 to 72%.

Four field trials comparing a less soluble potassium salt—potassium metaphmlphate—with superphosphate plus potassium chloride were laid down on soils of low K retention, and dry matter yields were measured over an 18-month period. At three sites the potassium metaphosphate treatment showed significant increases in one year, but not in the other. At the fourth site significant yield increases of 10% were obtained in both years.

Potassium metaphosphate has the advantage of lightness, being only about one-third the weight of an equivalent potassic-superphosphate mixture. Its disadvantages are lack of sulphur and a fixed K: P ratio.