Title: Nitrogen Management in Michigan Christmas Tree Plantations
Author(s): David E. Rothstein & Audria L. Holcomb, MSU Department of Froestry; Jill O'Donnell, MSU Extension
Where Published: Nursery, Landscape and Christmas Tree Research Projects and Educational Programs
Research Dates: 2000-2003
Subject Area: Fertilization & nutrition of Abies fraser
Summary: There is increasing concern over the effects of nitrogen (N) to the global ecosystem. Negative effects of N enrichment include: contamination of drinking water, buildup of algae (and corresponding loss of oxygen) in aquatic ecosystems, loss of biodiversity in terrestrial ecosystems, acidification of soils and groundwater, and global climate change brought about by emissions of nitrous oxide (N2O). Nearly 75% of global release of N is associated with fertilizer inputs in food and fiber production.
The production of horticultural crops such as Christmas Trees has the potential to contribute significant amounts of N to the environment - one that has received relatively little attention in sustainable ag research. In Michigan alone, there are 60,000 acres of land devoted to Christmas Tree production. Because Christmas Trees in Michigan are often planted on sandy soils, the potential for losses of N due to leaching may be particularly high.
Objectives
1. Determine the most efficient level of N application for Fraser fir production.
2. Understand fate of N fertilizer applications to Christmas Trees.
3. Compare the economic and environmental costs.
About the Project
In the spring of 2002, we initiated a study of the response of Fraser fir plantations to varying rates of N addition. We added N to four-year-old trees at 0, 0.5, 1.0 and 1.5 ounces of N per tree. These rates correspond to 0, 50, 100 and 150 percent of the amount recommended for four-year-old trees in Michigan.
Nitrogen was added as ammonium sulfate in a single surface application around the drip line of each tree. These trees were planted in 1998 on loam soil at the MSU Forestry Department's Tree Research Center (TRC) in East Lansing, Mich. Prior to this experiment, the trees had never been fertilized.
Each spring we measured the height, leader length, lateral buds and basal diameter of all trees. Throughout the growing season, we collected soil cores (8 in. depth) from the dripline of two randomly selected trees per plot to determine mineral N (ammonium and nitrate) availability. In October 2002, we collected foliage to determine foilar N concentrations. We used these estimates, together with measures of N concentration, to estimate the amount of N taken up by each tree (above ground only) over the 2002 growing season.
Tension lysimeters were installed below the rooting zone of three randomly selected trees in each plot to monitor N concentrations that had leached into soil water. Lysimeters were sampled weekly between April and June of both 2002 and 2003 and analyzed for N in the form of ammonium and nitrate.
Results
We found that springtime applications of fertilizer produced marked increases in available soil N that were sustained throughout the growing season. We also noticed that extractable N levels in soil remained elevated int he 1 and 1.5 oz./tree treatments in early spring 2003 - a full year after the 2002 fertilization. Control plot trees (which had never been fertilized) had foliar N levels below the 1.5% deficiency threshold defined by Fisher (1996) for Fraser fir in Michigan.
Fertilization resulted in a significant increase in foliar N relative to the control; however, there was no apparent response to additions greater than the lowest rate of 0.5 oz./tree. Fertilization had no effect on rates of 2003 height extension or basal diameter growth between 2002 and 2003. In addition, we could find no evidence that fertilized trees took up any more N than control trees. Taken together these data suggest that there is no benefit to adding N at levels above 0.5 oz./tree.
In contrast, the environmental costs of fertilization increase markedly with increasing levels of N addition. Nitrate concentrations of leachate water increased consistently with each increment of added N water (10 mg/L as N). In fact, we frequently recorded concentrations in excess of 200 mg N/L in the highest addition rate treatment. This pattern of nitrate concentration detected in the leachate water resulted in clear increases in leaching losses of N with increasing additions of fertilizer.
Conclusions
1. Some N fertilization is necessary, as unfertilized trees appear to be N deficient (yellow).
2. We can find no benefit to N additions above 0.5 oz./tree.
3. Additions above 0.5 oz. of nitrogen/tree result in significant quantities of N escaping the rooting zone, potentially contributing to groundwater contamination.
To obtain copies of this report, contact:
Jill O'Donnell
Michigan State University Extension
401 N. Lake Street, Suite 400
Cadillac, MI 49601
Phone: 231/779-9480
E-mail: odonne10@msu.edu
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