2019 ASHS Annual Conference

Prior to dormancy, deciduous fruit trees return mobile nutrients such as potassium (K) from senescing leaf tissue to reserve organs. These nutrients are remobilized the following growing season to developing vegetative and reproductive organs. Excessive K fertilization is common in fruit tree orchards in the southeastern U.S. but higher applications do not necessarily turn into higher concentrations within the fruit. Thus, there is a need for understanding K cycling in trees that receive high K applications. The objective of this research is to determine if high application rates of K are absorbed and primarily mobilized to reserve organs or if uptake is limited and the excessive K is lost from the soil. Three-year-old peach trees were fertilized at two different rates: 1) 136 g tree^-1 (grower standard); or 2) 680 g tree^-1 K₂SO₄. Leaf K concentration was quantified during the summer and senescence between October and December. Winter tissue samples from new shoots and older shoots along with soil samples from a depth of 0.15 and 0.45 m were taken to understand resorption proficiency and to quantify leaching, respectively. Trees applied with a higher rate of K had higher leaf K concentration (2.77 ± 0.05%) compared to the standard rate (2.19 ± 0.07%, F = 42.3, P < 0.001) along with each date of sampling (P < 0.01). Shoots from trees which received a high rate of K had statistically higher K concentrations (0.68 ± 0.01%; t = 2.15, P < 0.05) than the grower standard trees (0.62 ± 0.01%), although these values do not account for resorption of excessive K applications, suggesting most excess of K may have been lost rather than an increase of K absorption. With additional soil sampling and tree analysis, these results may provide growers an understanding of potassium longevity within orchard systems and optimize fertilizer applications.