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Hybrids between Corylus avellana and Corylusamericana are one of several new perennial and winter annual crops being developed as part of the Forever Green Initiative at the University of Minnesota. As a woody perennial shrub, hazelnuts in agroforestry systems can provide a new revenue source for rural landowners; continuous living cover to prevent soil erosion, sequester soil carbon, protect water quality, and provide wildlife habitat; and a delicious and healthful new local food. If hazelnuts are to fulfill their potential, better germplasm and better nitrogen fertilization recommendations are both needed. We modeled these trials after trials by R.E. Worley, who showed that yields of pecan trees fertilized only when leaf nitrogen (N) fell below critical thresholds were maintained with lower levels of applied N, benefitting both the environment and growers' profits. Results of trials at three Minnesota sites, comparing N applied only when leaf N fell below 1.8%, 2.0%, or 2.2% with annual N applications and no N over 4 years, support using 2.2% leaf N as the critical threshold for N fertilization. Our results showed that whereas only 8% of N applied annually ended up in the harvested nuts and husks, N that was applied to plants that demonstrated hunger for it was more efficiently taken up. Our results suggest a need for more productive germplasm and further research to develop best management practices for N fertilization. [ABSTRACT FROM AUTHOR]

The article focuses on a study which assessed nitrogen (N) responses to variable rates of N applications to young established hybrid hazelnuts in the Upper Midwest of the U.S. trials were done in seed-propagated hybrid hazelnut plantings in Minnesota from 2003 through 2005. Results indicate variations in management system and soil conditions among the four field sites considered for the study. It was revealed that nitrate and ammonium were correlated with N application rates.

The article discusses a research on the responses of newly transplanted hybrid hazelnut seedlings to variable rates of nitrogen (N) in the field and the leaf and soil analysis as diagnostic tools in order to develop N fertilization rate recommendations for growers. N rate trials were done from 2003 through 2005 in three new hybrid hazelnut plantings in Minnesota. The plant mortality data supports the recommendations from Oregon to delay N fertilization until the second or third year after transplanting.

Hybrids of Corylus avellana, C. atnericana and C. cornuta, are being developed as a potential crop for the Upper Midwest of the United States, but little is known about fertilizer nitrogen (N) management. We hypothesized that N application when the bushes were most fully leafed out would result in highest N uptake efficiency (NUE). We used 15N-labeled ammonium nitrate to measure NUE from soil applications in mid-April, late April, late May, early August, and mid-September. Nitrogen applied in either mid- or late April never comprised more than 5% of the total N in shoots or leaves, suggesting that N used for early leaf expansion came primarily from stored reserves. Applications made after April demonstrated that N was quickly translocated to rapidly growing plant parts: May applications comprised 9% of the N in leaves collected in July; August applications comprised 12% of the N in nut kernels collected in September; and September applications comprised 9% of N in catkins collected in October. Nitrogen applied in August and September appeared in new shoots the following April at higher levels than it did aboveground the previous October, showing that N applied late in the season may be stored below ground over the winter. NUE was highest for August and September applications at one site and August and mid-April applications at the other, implying that summer is generally the best time to apply N for most efficient uptake. However, overall NUE was low, only 5% for August applications, suggesting a need to develop other methods of improving NUE in hybrid hazelnuts. [ABSTRACT FROM AUTHOR]