Annual applications of N, P, and K for four years moderately increase nut production in black walnut

Abstract

Annual applications of N, P, and K fertilizers were broadcast for 4 years around black walnut trees (Juglans nigra L.) in an upland plantation to determine their effect on nut production and foliar nutrient levels. Fertilization significantly (P = 0.05) increased nut production, treatments containing P with N and/or K being most effective. Doubling the rate of application did not produce a corresponding yield in nuts. Increases in leaf concentrations of N, P, and K were associated with increasing treatment levels of these elements. Levels of all elements tested, except P, were above deficiency levels. The modest gain in production suggests that soil fertility was not a major factor limiting nut production for trees in this study.