Annual applications of N, P, and K interrupt alternate-year nut crops in black walnut

Nut production and diameter growth at breast height of black walnut (Juglan s nigra L.) were measured for 5 years to determine the effect of nitrogen ( N) and potassium (K) fertilization separately, in combination, and with and without phosphorus (P) broadcast annually for 4 years at two rates. Fertil ization significantly (P > 0.05) increased nut production and diameter grow th. Treatments containing P with N and/or K were most effective for increas ing nut production, and treatments containing N were most effective for inc reasing diameter growth. Doubling the rate of application did not cause a c orresponding increase in nut production or diameter growth. Leaf levels of N, P, and K were within the adequate range, and the addition of N increased leaf N, but not P and K. The alternate bearing tendency that was present i n year 3 of the study was not apparent in years 4 and 5.