Nitrogen fertilization for new plantings of hybrid hazelnuts in the upper midwest of the United States of America

Seed-propagated hybrids of Corylus avellana and C. americana are a potential crop for the Upper Midwest. Current N recommendations for hazelnuts are based on research on clonally propagated C. avellana in Oregon and may not be applicable in the Upper Midwest due to differing soils, climate, and plant genetics. We established three field plots in 2003 to test N fertilization rates on new plantings, with rates up to 33 g N plant^-1 as ammonium nitrate applied annually in the spring, starting 2 wk after transplanting. We observed a strong negative linear effect of N rate on plant survival. In the second year we added trials on same-aged plants that had not previously been fertilized and found no N effect on survival. We concluded that waiting 1 yr after transplanting before fertilizing increases plant survival, but even then N requirements during establishment years are very low for hybrid hazelnuts. Standard leaf N concentrations for C. avellana in Oregon are roughly applicable to hybrid hazelnuts, except that the threshold between deficiency and sufficiency should be raised slightly to 1.9% N. The current threshold between deficient and sufficient, 2.2%, should be regarded as a target, rather than as a threshold to be exceeded.