Nitrogen Fertilization for Hybrid Hazelnuts in the Upper Midwest

Nitrogen Fertilization for Hybrid Hazelnuts in the Upper Midwest

Summary

Field work has been completed for all three years of this project. Laboratory work is in process for the final year, with final data analysis waiting for the results from the lab.

Preliminary results suggest that young hazelnuts do not need much if any nitrogen fertilization as long as soil organic matter is moderate. High rates of N applied as ammonium nitrate are toxic to young hazelnut transplants. Older plants do not show immediate response to N, but may respond after two or three years depending on the level on organic N present in the soil, though these results have not yet been definitively confirmed by our research. Hazelnuts, like most woody plants, appear to be very efficient users of N, because of their ability to store N in their roots and bark over the winter for reuse the following season. Nut production is likely to increase N demand.

Our tentative conclusion is that the N fertilization recommendations developed for European hazelnuts in Oregon are probably applicable to hybrid hazelnuts in Minnesota.

Objectives/Performance Targets

Nitrogen is the most important nutrient for hazelnuts and is also the nutrient that can do the most harm if applied in excess. We will develop two N response curves for Minnesota-hardy hybrid hazelnuts: 1) for new plantings, to determine optimal N rates for rapid growth and early nut-bearing, and 2) for mature plantings, to determine maximum sustained economic yields. With 15N tracer studies we also hope to determine the optimal time of year in which to apply nitrogen to hazelnuts.

Accomplishments/Milestones

In 2003 we established three new plantings, all on experiment station land within 60 miles of the UM campus. All sites had low organic matter soil. Treatments were N rates of 0, 2.5, 5, 10, 20, 30g N plant-1 (0, 10, 20, 40, 80, and 120 lbs acre-1), applied in the spring, plus one split spring plus fall treatment. Treatments were replicated five times at each site in a randomized complete block, with five genetic lines nested within N rates. Results from 2003 indicate that even the 10g N plant-1, a relatively low rate, is too high for new transplants: rates higher than 10 g N plant-1 resulted in high seedling mortality. This supports recommendations to delay fertilization until the second year. Measurements taken at the end of 2004 showed no statistically significant differences in growth between the controls and the 10 g N plant-1 rate, but the leaves of the controls were starting to show visual signs of N deficiency (leaf chlorosis), which became even more marked in 2005. Leaf N in 2004 was optimal for bushes receiving from 2.5 to 10 g N plant-1 year-1, but toxic for plants receiving more than that. Data for 2005 has not yet been analyzed.

In 2003 we also established N trials in four established plantings, two on experiment station land, inherited from other researchers, and two on farms in collaboration with growers. All of these plantings were planted in 2000, with the exception of one 1997 on-farm planting. The treatments were the same as for the new plantings. Blocking was by previous treatment, genetic line, or soil type, depending on the site, with three to eleven blocks per site. Results from 2003 showed an increase in leaf N with increasing N application rate at two of the sites, but none at the other two sites. There were no significant growth responses at any site in the first year. In 2004 an additional site showed a leaf N response, but still no growth responses were observed. In 2004 some bushes began to produce nuts; nut yield was weakly correlated with bush size, but not with N application rate nor with leaf N. These results are as expected because there is frequently a delay in response to N fertilization in woody plants which may initially store N. In 2005 leaf chlorosis began to be visible in the controls at Staples, where the soil is very sandy; it is expected that 2005 growth data and leaf analysis data will show significant N rate effects at Staples, but probably not at Montevideo where the high organic matter soil is rich in mineralizable N.

Tracers: In the fall of 2004 we started a pilot study to determine the optimal timing of N applications using 15N tracers, and found that N applied on September 1 was readily taken up whereas N applied on September 21 was not. In 2005 we applied tracers on April 11, April 25, May 25, July 31, and September 9 to see which is best. Laboratory results are expected soon.

Impacts and Contributions/Outcomes

In 2005 Lois Braun presented preliminary results as a poster at the conference of the Association for Temperate Agroforestry, and as a paper in the conference proceedings. In addition, she gave a talk at the annual meeting of the Northern Nut Grower’s Association, which is written up in their journal.

The outcome expected from this project is the development of accurate recommendations for nitrogen fertilization rates and fertilization timing for hybrid hazelnuts in the Upper Midwest.

Collaborators: