Method of Nitrogen Application in Summer Affects Plant Growth and Nitrogen Uptake in Autumn in Young Fuji/M.26 Apple Trees

Abstract

Effects of foliar vs. soil nitrogen (N) application during the summer and the autumn were studied in young Fuji apple trees (Malus domestica Borkh) on Malling 26 (M.26) rootstock. One‐year‐old bench‐grafted trees were potted in 3.8‐liter pots in a mix of perlite, peat moss, and loam soil (1:1:1 by volume) and were treated weekly from late June to early September with 0.5% urea either by foliar or soil application or soil application of water (control). At the end of September, five trees from each treatment were harvested, and shoot and root growth and leaf N concentration were determined. In mid‐October of the same year, trees from each treatment were randomly divided into three subgroups. One group received soil application of water (control), and the other groups received either a foliar or soil application of 3% 15N‐urea. After natural leaf defoliation, trees were harvested, and total N and 15N concentration of stems (all aboveground tissue) and roots was determined. Regardless of application method, N application during the summer promoted plant growth and increased leaf N concentration. Soil N application during the summer stimulated more shoot and extension root growth than foliar N application. In contrast, the foliar N application in the summer promoted more feeder root growth than soil N application. Regardless of application method, autumn N application after terminal bud set had little effect on current‐year growth but increased total plant N concentration. In the autumn, trees that received soil N applications in the summer had more 15N uptake by leaves, while trees receiving foliar N applications in the summer had more 15N uptake by root. These results suggest that the differential influence of N application methods during the summer on growth and partitioning of trees affects tree responsiveness to autumn N applications. The use efficiency of autumn‐applied N depends on the method of N application in the summer.