Drip-fertigation of apple trees affects root distribution and development of K deficiency

Abstract

The locations of root intersections were mapped relative to micro-emitters in spring, 1996 for Gala apple (Malus domestica Borkh) on M.26 rootstock, which were established and grown for 8 yr under micro-irrigation with fertigation. Root distribution was mapped for trees that had been irrigated daily between May and October using drip or microjet systems and fertigated each year during May. Drip-irrigated trees had nearly half of their total root intersections within 30 cm depth and lateral distance from the emitter. Roots of microjet-irrigated trees were more widely distributed over a soil volume extending to 60 cm depth and 90 cm lateral distance from the trees. Leaf K concentrations had decreased to near deficient concentrations for drip-irrigated trees after 5 yr.Root distribution mapping and soil sampling were undertaken in spring 1997 for N-fertigated Gala on M.9 apples, planted in 1992 on the same soil, with or without annual K applications during 1992–1996. Fertigation of 15 g K tree−1 each year in July–August did not affect root distribution, which remained laterally and vertically restricted but prevented the decline of exchangeable soil K below 50 mg kg−1, exchangeable K/Ca + Mg + K ratios below 0.04 and the appearance of K deficiency symptoms in the trees. There was no evidence of long-term soil-K enrichment after 5 yr of K fertigation. Key words: Leaf and soil K, micro-irrigation, Malus domestica Borkh, root restriction