DEVELOPMENT AND CORRECTION OF K-DEFICIENCY IN DRIP-IRRIGATED APPLE

Various schedules of 40 g N and 17.5 g P/tree per year were applied wi th irrigation water (fertigation) to 'Summerland McIntosh' apple (Malu s xdomestica Borkh.) trees on M.9 rootstock commencing the year of pla nting. Leaf K concentrations averaged 0.82% dry mass, indicating defic iency, by the third growing season, This coincided with extractable so il K concentrations of 50-60 mu g . g(-1) soil in a narrow volume of t he coarse-textured soil located within 0.3 m of the emitters. The decl ine in leaf K concentration was reversed and fruit K concentration inc reased by additions of K at 15-30 g/tree applied either as granular KC l directly beneath the emitters in spring or as KCl applied as a ferti gant in the irrigation water, K-fertilization increased fruit red colo r, size, and titratable acidity only when leaf K concentration was <1 %, Fruit Ca concentration and incidence of bitter pit or coreflush wer e unaffected by K application. NPK-fertigation commencing upon tree es tablishment is recommended for high-density apple orchards planted on similar coarse-textured soils.