THE INTERACTION EFFECTS OF POTASSIUM AND DROUGHT IN FIELD-GROWN BARLEY .1. YIELD, WATER-USE EFFICIENCY AND GROWTH

In order to study the interaction of K application and drought a field experiment with spring barley (Hordeum distichum L. cv. Gunnar) was conducted in 1985, 1986 and 1987 on coarse-textured sandy soil low in natural K content and water-holding capacity. The drought occurred naturally or was imposed by shelters during the grain-filling period. K was applied as KCl at rates of 50, 125 and 200 kg K/ha top-dressed at emergence. High K applications (125 and 200 kg K/ha) significantly increased rate of growth of the vegetative parts of the crop. With high K application the leaf area increased up to 26% at anthesis, and top dry matter accumulation increased up to 15% between anthesis and milk-ripe stages of growth, resulting in about 10% higher straw yield at final harvest. Also, the number of ears increased with high K application. Final grain yield was unaffected by level of K application in fully irrigated plots. Drought during the grain-filling period decreased grain yield by decreasing grain weight and number of grains per ear. However, with high K application at medium level of drought, reduction in grain yield tended to be less. Water-use efficiency (WUE) for total dry matter production was increased up to 12% by high K application; however, WUE for grain production was unaffected by the level of K application. High K application significantly increased root density in the subsoil in the wet year of 1987, while in the dry year of 1986 no differences could be detected between K levels. Despite the low effect of high K application on final grain yield, the induced increase of the vegetative dry matter accumulation is of economical importance when the total above-ground biomass of the barley crop is used for cattle fodder.