ROOTED INRESEARCH
DATA DRIVEN GROWTH: MODELING FACTORS AFFECTING KENTUCKY BLUEGRASS AND TALL FESCUE LEAF AND ROOT GROWTH
By Cale A. Bigelow, PhD
It’s time for another installment of “Rooted in Research,” where we take a deep dive into turf research you can use or at least gain an appreciation for the science behind the art of turf systems management. Increasingly turf managers are interested in using data to help implement management decisions. Tis is especially true with respect to timing cultural inputs to manage/promote shoot production or anything that might enhance root growth/health. For this article I pondered the question, “How do cool-season grasses grow?” and dug into the classic vinyl LP section of the turfgrass literature. In my search, I identified three experiments that studied key factors affecting tall fescue and Kentucky bluegrass leaf and root growth.
Question #1: How does temperature affect leaf growth of diverse populations of tall fescue? (Nelson et al., 1978). In this experiment the researchers knew that, in general, total above ground leaf biomass was controlled by the leaf growth rate and length of time and temperature with a previously reported temperature optimum of about 77 degrees F (25 degrees C). It was also reported that leaf growth responses were more affected by changes in daytime than nighttime temperatures. What was not well studied, however, was how much of a difference there was among plants collected from different geographic regions. From a practical standpoint, plants capable of producing a lot of biomass may require more frequent mowing. Alternatively, these might be just what an athletic field manager may desire because they might be more traffic tolerant. Further, if the plant grows more vigorously in cold or warm weather, this could be very desirable in certain situations.
So, researchers collected plants from Mediterranean, Continental Europe as well as some experimental lines including a selection from the transition zone (Missouri) of the USA. Tey subjected the plants to a range of temperatures (50, 59, 68, and 77 degrees F) (10, 15, 20, and 25 degrees C)
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Figure 1. Overview of generalized cool-season seasonal shoot and root growth. TPI Turf News September/October 2022
with a 16 hour daylength as well as a cooler temperature, 46 degrees F (7.78 degrees C), with an eight hour daylength. Tey then painstakingly measured “leaf elongation rates,” by watching for when collar formation occurred on select new leaves and measuring the distance from the collar to the leaf tip for various leaves as they emerged each and every day. Tis information was then mathematically manipulated to determine leaf elongation rates. Not surprisingly, what they found was that tall fescue leaf area, weight, and elongation rate were highest at 68 or 77 degrees F (20 or 25 degrees C) with a 16 hour daylength that steadily decreased with decreasing temperature. Tey also found that there were different responses to temperature among tall fescues from different geographic regions. Te authors suggested that these differences may be useful when breeding tall fescues for use in different climates. For example, if you planned to plant tall fescue in a warm-humid/transition zone and need vigorous growth in late-spring or summer, cultivars developed from plants native to a warmer region may be more appropriate.
Question #2. Can Kentucky bluegrass root growth be predicted by using a degree-day accumulation technique? Researchers in Central Ohio (Koski et al., 1988) were interested in how soil temperature changes from January to June affected spring root growth. Prior work reported that 60-70 percent of the bluegrass plant’s total seasonal root growth occurred during those months. For this study, they were interested in how much rising spring soil temperatures affected root growth. Te field experiment was conducted in the Ohio State University Rhizotron facility.
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