A new look at fertilizer guidelines

Features - Fertilizer

First-year results reveal CRFs enhance caliper of field-grown nursery trees.

Oak at Connon AVK: the Polyon 20-06-13 treatment (above) versus the 19-19-19 treatment (right). Leaf size is significantly smaller with the 19-19-19. Pictures taken in July 2009.The green movement in the United States has forced the examination of past field fertilization practices to determine whether they are environmentally sound and based on scientific research.
Field-grown nursery stock has traditionally been fertilized with soluble field-grade fertilizers customarily applied in top dress, spilt applications at the recommended rates of 220 to 264 pounds per acre. These applications are completed in late spring on or before mid- to late-June and mid- to late-autumn before a “normal” freeze. A late fall application after a “hard freeze” or one in early spring — four to six weeks prior to the beginning of growth — could be used in replacement of one of the split applications. However, these late fall or spring applications were recommended for species with determinate growth such as most deciduous shade trees.
Soluble nitrogen products are usually finished by eight weeks after application. Nutrient availability in field-grade fertilizers is subject to rainfall. Heavy rain may wash away soluble nutrients before they can be absorbed, or summer droughts may delay release causing potential winter injury. Table 1 lists other conditions and weather factors that influence fertilizer applications. Several of the conditions and factors listed in Table 1 are issues for traditional soluble grade fertilizers and less so for controlled-release fertilizer (CRF) applications.

Click here to see tables and charts in PDF format

CRF field tests
The cost of natural gas — the primary raw material in ammonium nitrate — rose 113 percent from 2000-2007, and world fertilizer prices doubled in 2007 with another 18 percent increase in 2008. As a result, growers have become extremely interested in more efficient and efficacious fertilizer applications. Also, the costs of labor and fuel to apply split applications have increased. Information is lacking regarding CRF efficacy or improved efficiency with field-grown nursery stock.
In preliminary demonstrations at one Ohio nursery, the use of CRFs improved growth, eliminated split applications that are necessary with soluble-grade fertilizers, reduced summer pruning cost, winter injuries and maintenance procedures during the growing season.
CRFs can be banded approximately 1 inch below the soil surface using a 15- to 16-inch wide, grape (3-prong) hoe so that prills are less prone to wash away from the plant roots, be moved by mowing equipment or other cultural activities. Research has shown there is no advantage to banding fertilizer on two sides versus one. CRFs also release their nutrients over the growing season, which is more favorable for root uptake and use by the plant.

Materials and methods
Two cooperating nurseries in Ontario, Canada (Connon AVK in West Flamborough, Ontario and Braun Nurseries in Anacaster, Ontario), one in Ohio (Sunleaf Nurseries, Madison, Ohio) and one test site at Ohio State University (Waterman Farm, Columbus, Ohio) were evaluated. Tree liners of three species were used — Acer rubrum ‘Red Sunset’ (at Sunleaf, Braun and OSU); Acer rubrum ‘Embers’ (at Connon AVK); Pyrus calleryana ‘Chanticlair’ (at all sites); and Quercus rubrum (at Connon AVK). They were planted in mid-May, 2009 in Ontario and late April, 2009 in Ohio to be grown for three years or until the target caliper of 2 inches is reached. Three to five subsamples were used with five replicates planted in a split-plot design. All treatments were applied within two days of planting and will be applied again each spring for three consecutive years. The field dry-soluble (standard practice) fertilizer evaluated was 100 pounds per acre granular 19-19-19.
The CRFs used were Scotts Osmocote 33-3-6* (5-6 months) (2.5 tablespoons per tree), Osmocote 22-3-8 Plus Minors with Poly S (5-6 months) (3.0 tablespoons per tree), Polyon 36-3-6 (no minors) (26.6 grams per tree or 1.5 tablespoons per tree) and Polyon 20-6-13 (minors) (47.2 grams per tree). The Anderson DG formulations of AND 9135, 22-3-8 (3.8 tablespoons per tree) and AND 9136, 33-0-2 (2.7 tablespoons per tree) were used at all four sites.  Acer 23-4-9 (3 tablespoons per tree) and Acer 34-5-5 (2.5 tablespoons per tree) were used at Connon AVK for evaluation versus Osmocote. 50 pounds per acre N in spring after planting and 50 pounds per acre N in September was applied at Connon AVK as a conventional practice.
The Osmocote 22-3-8, Polyon 20-6-13, Acer 23-4-9 and Anderson 22-3-8 contained minors.

CRFs work on field-grown material
The Anderson 23 percent performed well at Sunleaf Nursery and provided excellent growth when tested on pear. The best treatment at Braun was Polyon 20 percent which also performed well tested with pear. The Polyon 20 percent was also one of the best treatments at Connon AVK, which was not significantly different than the high nitrogen-containing Acer 34 percent. Over location and species, the two Anderson treatments were not significantly different from one another and tested as well as industry standards of Polyon and Osmocote.
From this first year of results, it appears growth can be enhanced with CRF applications to field-grown nursery trees. No fertilizer had increased detrimental effects on maple growth over location and in ? caliper in oak. The lack of response to 19-19-19 is best shown at Connon AVK where the 19-19-19 provided some improvement over no fertilizer but not as much as with CRF formulations.
Elton Smith, formerly of Ohio State University, conducted an 18-year study of fertilization of two tree species. Smith noted tree growth improvement with yearly applications of nitrogen based fertilizers. However, by the ninth year of the study, Tilia cordata and Acer saccharum ‘Sentry’ both slowed in their fertilizer response. The results of Smith’s 18-year study provide the basis for many of the currently used guidelines today — the nitrogen rate of between 1 and 6 pounds per square foot; surface application and early spring timing. 
The results presented here are the first year of a three-year study that we hope will change fertilizer guidelines.

Sunleaf results
The species that was growing the fastest was ‘Red Sunset,’ followed by Chanticleer pear and red oak.
An analysis of change in caliper (? caliper) between May and September 2009, indicated red oak was reacting differently than the other two species to fertilizer treatments. The Osmocote 22-3-8 (5-6 months) formulation (which contained minors) provided significantly greater growth than the other six treatments.

Connon AVK results
November caliper measures taken at Connon AVK Nursery showed a significant treatment and species effect. Polyon 20 percent, Acer 34 percent and Connon’s conventional practice of 50 pounds per acre N after planting and 50 pounds per acre N in September were the best three treatments. A minor-containing fertilizer provided the best growth — in this case the Polyon 20 percent. Acer 34 percent provided the best growth for oak. 
The largest caliper species was pear, followed by oak and maple. The liner source for pear, oak and maple were different at Connon AVK from the other locations. The maple was a different Acer rubrum cultivar, ‘Embers.’ Red Sunset has more vigorous growth than ‘Embers,’ but ‘Embers’ has improved cold tolerance.

Braun, Waterman results
At Braun nursery and Waterman, the treatment by species interaction was significant for the pear. The two best treatments for pear were treatments containing minor packages.  

Hannah Mathers is associate professor, Department of Horticulture and Crop Science, Ohio State University, mathers.7@osu.edu. Luke Case is research associate, Department of Horticulture and Crop Science, OSU, case.49@osu.edu. Randy Zondag is assistant professor, OSU Extension, zondag.1@osu.edu. Kyle Daniel is graduate research associate, Department of Horticulture and Crop Science, OSU, daniel.161@osu.edu.