Revitalizing a Black Walnut Plantation Through Weed Control and Fertilization

Abstract

An 8-year-old, stagnating black walnut (Juglans nigra L.) plantation near Parkhill, Middlesex County, Ontario received applications of 6.7 kg/ha of active simazine in April of three successive years with or without applications of 100 and 200 kg/ha of elemental N. Elimination of 90% of the herbaceous competition increased 4-year diameter and height growth of the walnut trees by 153 and 222%, respectively. Fertilization with weed control further increased diameter and height growth. The response to N, however, was not proportional to the dosage of fertilizer applied and was not significantly greater than that obtained by weed control only. All treatments greatly increased the N content of the walnut leaves. Foliar N was still higher in all treated plots than in the control 4 years after treatment. Competition for N from broadleaf weeds and grasses is a major cause of growth stagnation in young black walnut plantations.