Drill and Fill and Other Field Nursery Fertilizer Application Techniques
Ted Bilderback, Carroll Williamson, Donald Breedlove, John Allen and
Mary Lorscheider

Introduction
Field grown nursery stock has traditionally been fertilized with soluble field grade granular fertilizers which are customarily applied in spilt applications as a top dress to established crops before bud break and in early summer. Nutrient availability in field grade fertilizers is subject to rainfall. Heavy rain may wash soluble nutrients away before they can be absorbed by roots. A summer drought may delay release of nutrients until late summer or fall, potentially causing a late flush and damage by early frosts or reduced acclimation and death due to winter freezing temperatures. Controlled release fertilizers (CRF’s) can also be applied as a one time per year top dress. However, growers consider CRF’s to be expensive and there is a lack of information regarding any improved efficiency or greater plant growth of field grown nursery stock.
In recent years, many field grown nursery crops have been irrigated with drip irrigation. With irrigation in place, nursery stock can be "fertigated" by injecting soluble fertilizers into the irrigation line. The annual rate of fertilizer application can be divided into several applications during the growing season. Liquid fertilizer can also be used to supplement granular field applications, particularly if rainfall has washed granular fertilizer away from plant roots.
The Drill & Fill fertilizer application technique is new in concept to field production of nursery stock. The Drill & Fill technique is very similar to the soil auger technique used for landscape shade trees by tree service companies for decades. The Drill & Fill method uses a drill or punch bar to create holes adjacent to field grown plants. CRF’s can then be placed below the soil surface, therefore less prone to wash away from plant roots or be moved by mowing equipment and other cultural activities. However, only a few grower observations provide any evidence of the benefit of this labor intensive fertilizer technique. Objectives of the study
The objectives of this study were to measure plant growth responses of test crops to Drill & Fill CRF application compared to Top Dress application of CRF; Liquid Fertilizer application distributed by the irrigation system during the growing season; dry granular fertilizer split applications and combinations of liquid fertigation, dry fertilizer surface application, Drill & Fill CRF and Top Dress CRF fertilizer application techniques.
Materials and Methods
One year in field, established plants of Ilex X ‘Nellie R. Stevens’ Holly and Ulmus parvifolia ‘Allee’ elm were selected as test crops. The study was conducted at Shiloh Nursery, Harmony, NC in cooperation with John Allen and Danny Allen owners of Shiloh Nursery. Other cooperators in the study were Donald Breedlove, Iredell County Horticulture Agent, Mary Kelly and Rick Helpingstine or Harrell’s Fertilizer Company and Ted Bilderback, Carroll Williamson and Mary Lorscheider of N.C. State University.
All plants in the study were drip irrigated. To conduct this study, 5 rows of nursery stock for each crop were selected. There were 360 ‘Nellie R. Stevens’ hollies and 360 ‘Allee’ elms included in the study for a total of 720 plants. On November 8, initial growth measurements were taken for each plant in the study. On Feb 7, 2003, each plant was measured again. ‘Allee’ elms were measured for height and caliper. ‘Nellie R. Stevens’ was measured for height, maximum width and minimum width. A growth index (GI) was calculated by averaging maximum and minimum width, adding height and dividing the sum by 2. Differences between initial measurements and data collected 15 months later were used to calculate an increase in for both test crops. Drill & Fill and Top Dressed Controlled Release Fertilizers samples were also collected Feb 7, 2003, sent to Pursell Industries, Sylacauga, Al and analyzed for percent of total nitrogen released.
Shiloh standard fertilizer practices included application of dry granular 17-17-17 before bud break in spring and application of NH4-NO3 (34-0-0) in June. Liquid fertilizer ( ) applied via irrigation lines was is used as a supplemental practice. Liquid fertilizer was applied in 5 applications during the growing season.
Controlled Release Fertilizer treatments were applied November 8, 2001 and January 29, 2002. A gas powered drill and 2 inch auger were used to create 2 holes six to ten inches deep on each side in line with the drip irrigation tubes. Eight ounces of 18-6-12 (8-9 month release) Harrell’s/Polyon fertilizer was deposited just beyond the root zone. The controlled release fertilizer was then covered with field soil. The same fertilizer product was also top dressed on each side of the plant at the same rate as Drill & Fill.Results
Analysis of release of the 18-6-12 Harrell’s/Polyon Controlled Release Fertilizer indicated that approximately 47% of the Drill & Fill and 36% of the Top Dressed CRF had released from November 8, 2001 to February 7, 2003 (Table 1). Considering that no more than one-half of the nitrogen in the controlled release fertilizers released, it would be expected that the CRF’s could influence growth during the 2003 growing season. A third follow-up measurement of growth responses in Fall 2003 would seem to be appropriate.
The amount of nitrogen fertilizer applied or released (available for plant adsorption) produced variable plant growth responses in both test crops. The combination Drill & Fill + Liquid + Dry Granular fertilizer treatment had the highest amount of fertilizer applied (6.9 oz N) and available (5.4 oz N), however ‘Allee’ elm had similar caliper in treatments with 1/3 rd the applied / available N. In contrast, for ‘Nellie R. Stevens holly, the highest rate was not among the best treatments. Additionally, there did not appear to be any preference for the fertilizer application technique. For example, the Liquid + Dry Fertilizer treatment produced the greatest increases in growth index for ‘Nellie R. Stevens’ but had one of the lowest increases in caliper for ‘Allee’ elm. No application technique used alone and/or in combination with other techniques produced the greatest growth responses in either crop. The most consistent fertilizer treatments were Dry Fertilizer, Top Dress CRF + Dry Fertilizer, and the Drill & Fill + Top Dress CRF which produced the greatest increase in growth in both species. Table 1. Summary of Treatments, Rates Applied and Available Nitrogen Per Plant
Fertilizer N Applied N Released ‘ Allee Elm’ ‘ Nellie R Stevens’
Treatment Plant/yr Plant/yr Increased Caliper Increased in GI
(oz) (oz) (mm)
Dry Fertilizer 2.0 2.0 23.7a 10.0 ab
Liquid Fertilizer 34-0-0 2.0 2.0 21.9b 9.7ab
Drill & Fill
CRF 18-6-12 2.9 1.4 23.4a 6.9bc
Top Dress
CRF 18-6-12 2.9 1.0 23.5 a 6.8bc
Liquid +
Dry Fertilizer 4.0 4.0 22.2b 10.2a
Drill & Fill +
Dry Fertilizer 4.9 3.4 22.2b 7.7ab
Top Dress CRF +
Dry Fertilizer 4.9 3.0 22.9a 8.8ab
Top Dress CRF +
Liquid 4.9 3.0 22.8a 6.7bc
Drill & Fill CRF+
Liquid 4.9 3.4 23.0a 6.9c
Drill & Fill CRF +
Top Dress CRF 5.8 2.4 25.1a 9.1ab
Drill & Fill CRF +
Liquid +
Dry Fertiizer 6.9 5.4 23.8a 7.1bc
Significance to the Industry
The Harrell’s/Polyon 18-6-12 (8-9 month) controlled release fertilizer had 47% of the N released from Drill and Fill method and 36% of the N released as a Top Dress application. Fertilizer application rate and the application technique did not provide conclusive results regarding effects on plant growth characteristics measured for either test crop. Residual growth response during the 2003 growing season is expected for the controlled release fertilizer treatments.

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