Verdure: Nitrogen, a plant growth regulator and shade ... oh my!

Do different shade levels influence N plus trinexapac-ethyl’s effects on turf?


Melvin Calvin, Ph.D., received the Nobel Prize in chemistry in 1961 for figuring out photosynthesis in plants, and it all starts with sunlight. When it comes to sunlight for turfgrass, it’s all about quantity and quality.

We know shade causes thinning of turfgrass stands and loss in surface quality and performance, but we don’t always have perfect, full-sun conditions to grow and maintain turf. There’s shade cast from trees at various times of day, and cloudy, overcast weather and low-light conditions at certain times of the year. We only have some basic understanding of what the change in wavelengths caused by tree lines does to turfgrasses, and, combined with a loss of light intensity, shade really causes us to scratch our heads.

Can nitrogen and a plant growth regulator help turf grow better under shaded conditions? Researchers at Ohio State University wanted to find out.

This study was conducted in 2006-07 at Ohio State’s Turfgrass Foundation Research and Education Center in Columbus, Ohio, on newly installed washed sod of Penncross creeping bentgrass maintained as a fairway (0.6 inch [1.5 centimeter] mowing height) on a California-style root zone, with 80/20 v/v sand/peat added, and a pH of 7.2.

First, three light environment blocks were set up: 1) plot area receiving shade from mostly mature deciduous maple trees (Acer sp.); 2) plots under a structure that held black perforated cloth that was considered neutral shade; and 3) full sun (no shade). Both shade areas had about 92% reduction in photosynthetic photon flux compared with the full-sun area — let’s call it heavy shade. Of note, tree shade altered the ratio of red to far-red light (0.39), while the artificial shade (1.28) and full sun (1.30) did not — a critical difference that does not get enough attention in shade studies.

In each environment block, fertilizer and plant growth regulator treatments were applied. Fertilizers tested represented three nitrogen (N) sources: urea (46-0-0), calcium nitrate (15-0-0) and ammonium sulfate (21-0-0). Each granular product was mixed with water to become a soluble solution, then applied in 2 gallon water-carrier/1,000 square feet (815 liters/hectare) from a standard CO2-powered backpack plot sprayer.

All fertilizers were applied at 0.08 pound N/1,000 square feet (0.43 grams N/square meter) once per week, and Primo (Syngenta; trinexapac-ethyl formulated at 1 pound a.i./gallon [120 grams a.i./liter]) was applied at 0.125 fluid ounces/1,000 square feet (0.39 liters/hectare) every two weeks from July to September 2006 and May to October 2007. All fertilizers were applied alone and with Primo, and plots were arranged with three replications, with untreated plots included. So, turf was subjected to three foliar fertilizers, each with and without Primo, and all under deciduous shade, neutral shade or full sun, in a complicated but well-planned multifactor field trial.

How did the turf respond? Turf in full sun was fine, of course. In heavy shade conditions prior to full leaf emergence in spring, turf growing conditions were optimal. But the focus and understanding then was retention of that turf quality, and like in many other shade studies, the combination of low N and Primo worked. All three N sources performed equal to each other in the shade, so select one that best fits a budget or program and combine with Primo to provide an acceptable creeping bentgrass stand and surface at fairway height of cut.

What happened to the shaded turf biochemically? Plots that received Primo showed total chlorophyll content increased by as much as 19% compared with untreated plots, which is why we often see greening of turf post-Primo applications, and those plots also had higher turf color ratings. There was also an increase in chlorophyll B content associated with those Primo applications, thus indicating potential shade adaption in the plant. Finally, flavonoids — considered abiotic stress defense compounds — showed a positive response from Primo applications, and this is an area that warrants further research.

Source: E.J. Nangle, D.S. Gardner, J.D. Metzger, J.R. Street and T.K. Danneberger. 2012. Impact of nitrogen source and trinexapac-ethyl application on creeping bentgrass (Agrostis stolonifera L.) physiology under neutral shade, deciduous tree shade, and full sunlit conditions. HortScience 47(7):936-942.

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.