Verdure: B is for boron

Elizabeth (Beth) Guertal, Ph.D., wrote 80 consecutive columns in GCM from May 2015 to December 2020. She named the column “Verdure,” which refers to the aerial shoots or green part of the plant that remains after mowing, or what she considers “the best part of the turf.” The column’s intent was to provide a short synopsis of a research article published in a scientific journal that has applications for the golf course turf manager.

Dr. Guertal reviewed articles from many research journals where turfgrass scientists publish their work, including Agronomy Journal, Crop Science, HortScience and Weed Technology. The author most frequently cited in those columns was Peter Dernoeden, Ph.D., professor emeritus at the University of Maryland, who, incidentally, was my doctoral adviser. On behalf of your loyal readers, thank you, Dr. Guertal, for your wonderfully written and insightful contributions to GCM. It is an honor and a privilege to carry on this column and retain the “Verdure” name and tradition.

Dr. Guertal liked to begin each new year with a look at turfgrass research published “waaaay back.” In her honor, let’s take a look at one of her earlier research publications.

The topic is boron, a chemical element designated by the letter B. Most boron is used in fiberglass for insulation, polymers, ceramics and borosilicate glass. Boron is also an essential plant nutrient, with borax and boric acid compounds used as fertilizers.

One experiment was conducted in the greenhouse at Auburn University and initiated in December 1998. One-inch-diameter (2.54-centimeter-diameter) containers were filled with a root-zone mix of 85% sand and 15% reed sedge peat, and seeded with three creeping bentgrass cultivars (Crenshaw, Dominant and SR1020). When the seedlings were 21 days old, emerged plants were removed to leave only one per container. A boric acid fertilizer solution in 1 fluid ounce (30 milliliters) water was applied to each container once a week for eight consecutive weeks at 0, 0.5, 1, 2 or 3 parts per million (0, 0.5, 1, 2 or 3 milligrams/kilogram) boron. Eight weeks after that, seedlings were removed, and shoot and root growth were measured. With three creeping bentgrass cultivars and five boron rates arranged with multiple replications, a total of 600 containers (or “plots”) were used for this study.

Key finding: For all three creeping bentgrass cultivars, increasing applied boron resulted in more turf growth (measured as shoot oven-dry weight), but root growth was not affected (oven-dry weight), there was no effect on turf color, and no turf injury was observed among any of the treatments.

A second study was conducted at the Auburn University Turfgrass Research Facility on a putting green grown in loamy sand, with 18-month-old plots of nine creeping bentgrass cultivars: Crenshaw, Dominant, L-93, Penncross, Penn A-2, Penn G-1, Penn G-2, Penn G-6 and SR1020. Boron was applied as sodium borate (20.5% boron) in 50 gallons water carrier/acre (468 liters/hectare) at 0, 0.5, 1 or 2 pounds/acre/year (0, 0.55, 1.1 or 2.2 kilograms/hectare/year). Each cultivar received 12 monthly applications in four replications from March 1999 through June 2001.

Key finding: Applying up to 2 pounds/acre/year of boron as fertilizer had no effect on turf growth, turf density, turf color or thatch for all the cultivars, and no turf injury was observed among any of the treatments.

Why is boron listed on soil test reports? Plant-available boron in soil takes the form of boric acid, which comes from decomposing organic matter. Boron is not bound to clay or organic matter and can leach like nitrogen. In agricultural crops, boron deficiency can occur in coarse-textured soils low in organic matter, and some forage crops, some vegetables and sugar beets are sensitive to low levels of boron in the soil. A soil test report will typically include a boron recommendation for those crops. Boron is normally present in dry turf tissues in a range of 6 to 30 parts per million (6 to 30 milligrams/kilogram).

In 1923, British botanist Katherine Warington was the first to identify boron as an essential plant nutrient. Although the exact function of boron in plants is not fully understood, plant physiologists have shown it plays a critical role in cell wall synthesis and structure.

Source: Guertal, E.A. 2004. Boron fertilization of bentgrass. Crop Science 44(1):204-208 (https://doi.org/10.2135/cropsci2004.2040).

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Mike Fidanza is a professor of plant and soil science in the Division of Science at the Penn State University Berks Campus in Reading, Pa. He is a 19-year member of GCSAA.

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