Tree Fertilization for Fine Root Growth and Whole Root System Effects

Summary: Grass and tree fertilization programs for fine root growth and whole root system effects juggle natural litter, tree age and health and site conditions.

broadcast (left) and drill hole (right) systems for tree fertilization are administered within the drip line: Fertilizer Application (e-TESDA), Public Domain, via Technical Education and Skills Development Authority of the Philippines

An article for the January 2017 issue of Arboriculture & Urban Forestry announces the results of four-year research into tree fertilization for fine root growth response and for whole root system effects.

Angela Hewitt and corresponding author Gary Watson of The Morton Arboretum in Lisle, Illinois, base their findings upon nitrogen fertilization with or without growth-regulating paclobutrazol (PBZ). They commence Fine Root Growth Response to Soil-Applied Nitrogen and Paclobutrazol with arborists primarily choosing nitrogen for routine maintenance fertilization of non-nutrient-deficient, suburban and urban trees.

The American National Standard Institute (ANSI) A300 Standard for Tree Care Operations (Part 2) describes enhanced root development and function among fertilization's deficiency-fighting, growth-defined, need-based objectives. It encourages annual landscape tree fertilization rates 10.6 times that of nitrogen estimated as excluded from natural nutrient cycling through fallen leaf and twig litter removal.

Previous research finds tree fertilization applications facilitating fine root growth with large crowns and unbalanced root:shoot ratios and favoring overall root system development in low-nutrient soils.

Studies give younger and older trees age-, goal-, size-determined nitrogen fertilizer rates, well beyond natural loss through litter removal, at 1.44-2.88 and 0.96-1.44 kg N/100 m2/yr. The difference theoretically heads older trees into favorable root-crown balances and moderate growth and vigor rates and helps younger trees with rapid growth into mature sizes. It ignores leaching to tree roots, at under 1 to around 71 percent, of recommended, same-rate yearly nitrogen fertilization programs for cool- and warm-season turfgrass varieties.

Fine root growth and whole root system effects concurrently juggle opportunistic leaching and tree fertilization with same-effect broadcast fertilization, granule-filled drilled holes and liquid injection applications.

The study keeps as its objective whole root system effects of broadcast or injected nitrogen on young ash (Fraxinus) and maple (Acer) and mature oak (Quercus).

Eighteen white (Quercus alba) and 36 bur (Q. macrocarpa) oaks live off three-year, low phosphorous-correcting, triple super phosphate (0-45-0) applications in poor-draining, undisturbed Nappanee silt loam. They manage first-year, one-time PBZ basal soil drenches and, in May and August, yearly granular 38-0-0 fertilizer, for leaf area and twig growth measurements every August. Dumas method-friendly nitrogen analyzers, Kjeldahl method-friendly samplers, Minolta meters and root density cores respectively note foliar nitrogen, total soil nitrogen, chlorophyll content and fine root growth.

The tree fertilization study obtains whole root system measurements by isolating 12 black maples (Acer nigrum) and 30 green ashes (Fraxinus pennsylvanica) with trenches at midpoints.

Nu-Gro Nitroform fertilizer (38-0-0) provides broadcast applications for 15 green ash, granular applications and injections for another 15 green ash and injections for all black maples.

Fertilizing the top 3.94 inches (10 centimeters), with or without PBZ, quickens fine root, not leaf or twig, growth and similar leaf area and nitrogen content. The Watson study from 1994 in contrast reveals significant fine root growth locally near injections and respects common practices of granular nitrogen quick-release fertilizer-filled drilled holes. Quality, undisturbed soils suggest established whole root systems and maximum fine root density unneedy of fertilizer and PBZ applications perhaps more appropriate for disturbed, unbalanced landscapes.

Grass and tree fertilization applications inconsistent with natural litter inputs and unclaimed by trees for fine root growth and by turfgrass turn landscapes into leached wastelands.

drill hole system for fertilization observes drip line boundaries; drilled holes allow for penetration of soil by air and fertilizer: Tom Hall/Georgia Forestry Commission/Bugwood.org, CC BY 3.0, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet;
University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

broadcast (left) and drill hole (right) systems for tree fertilization are administered within the drip line: Fertilizer Application (e-TESDA), Public Domain, via Technical Education and Skills Development Authority of the Philippines @ http://e-tesda.gov.ph/Fruit_Grower/Mod4/M4_L2_fertilizerapplication.html

drill hole system for fertilization; drilled holes allow for penetration of soil by air and fertilizer: Tom Hall/Georgia Forestry Commission/Bugwood.org, CC BY 3.0, via Forestry Images @ https://www.forestryimages.org/browse/detail.cfm?imgnum=1361178

For further information:

American National Standard Institute. 2011. American National Standard for Tree Care Operations -- Tree, Shrub, and Other Woody Plant Management -- Standard Practices (Soil Management a. Modification, b. Fertilization, and c. Drainage) (ANSI A300, Part 2). Londonderry NH: Tree Care Industry Association, Inc.

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