NITROGEN MANAGEMENT IN OREGON HAZELNUTS

An estimated 3,181,818 kilograms of nitrogen fertilizer is applied annually to Oregon's approximately 11,736 hectares of hazelnut orchards. The urea form applied to the soil in the spring is the most widely used practice in the industry. Research at OSU has shown the optimal level of nitrogen in the leaf tissue in August to be 2.2 to 2.5% N dry weight. Deficiency levels are 1.8 to 2.2%, and severe deficiency is considered anything below 1.8%. A recent ten year average of 1867 leaf tissue tests showed that 37% of the samples were in the normal range, 17% were above normal, and 2% were excess. There were 39% of the samples that showed below average levels, and 5% had deficient levels of nitrogen. Recent OSU research using isotopically labeled nitrogen showed that the rate of recovery of ground applied nitrogen for 'Barcelona' cultivar was 28%. The hazelnut tree was shown to have a strong reliance on nitrogen reserves that were mobile within the tree. The nut tissue was a strong sink for nitrogen. Stored nitrogen was readily available to fuel early spring growth. Uptake of nitrogen applied to the ground in spring progressed slowly in the first month after application and then peaked in the late summer. Fall applied foliar urea was absorbed into the tree and was readily available for spring growth. Recent trends in foliar fertilizer use in Oregon's hazelnut industry will be reported.