The phosphorus nutrition of the apple tree. II.* Effects of localized phosphate placement on the growth and phosphorus content of split-root trees

Abstract

Effects of localized placement of superphosphate on the growth and phosphorus content of young apple trees were studied in two successive pot experiments with split-root trees grown in soil. Over a 2-year period both nil and excess superphosphate depressed tree growth, but localized applications of low to moderate rates of superphosphate only slightly depressed total tree growth, compared with uniform application of fertilizer to root parts. This suggests that non-fed root parts are supplied with sufficient phosphorus through redistribution within the tree to maintain active root growth.

Tissue analysis clearly showed that the phosphorus content of tree tops in both experiments was dependent upon the proportion of root fertilized as well as the rate of fertilizer applied. However, the uptake of phosphorus by a root part was largely independent of whether superphosphate was applied to the other root parts. Further, a1 low (50–100 g per pot) but not high rates (200 g per pot or higher) of superphosphate, a higher phosphorus uptake per tree resulted from a uniform application of superphosphate than from an equivalent localized application.

Although the trees absorbed phosphorus from localized application in proportion to the rate applied, analyses showed that a non-uniform distribution of phosphorus persisted within the trees even after two growing seasons. In particular, the concentration of phosphorus in non-fed roots remained low irrespective of the concentration in the roots in the fertilized zone. Therefore, while apple trees may be able to take up phosphorus from localized placement in proportion to the rate of superphosphate applied, the distribution of that phosphorus in trees following uptake may be non-uniform. The significance of this for tree performance in the field needs assessment in the long term.

____________________ *Part I, Aust. J. Agric. Res., 26: 843 (1975).