Figure 2. Diagram of the rhizotron experimental laboratory from: Karnok and Kucharski “Design and construction of a rhizotron- lysimeter facility at Te Ohio State University.”
You might ask, what the heck is a Rhizotron? Briefly, a rhizotron is a below-ground laboratory facility that allows for the ability to continuously observe roots and factors affecting root growth without destroying the plant and under a field environment setting. Grasses are planted in small cells containing a consistent rootzone media, often a porous sandy media. In the below ground laboratory, each cell has a small door to exclude light and the door opens to a slanted glass root observation window. As roots grow down, they encounter and imprint themselves on the glass, allowing researchers to observe and measure characteristics of interest like root number, appearance/disappearance, length, and diameter. Using the Rhizotron, researchers can manipulate above ground cultural inputs like mowing height and fertility, or study below ground factors like rootzone temperature.
In the present study, researchers monitored the effect of soil temperature at 4 inches (10.16 cm), for three winter-spring seasons on ‘Baron’ Kentucky bluegrass. Te intent was to develop a mathematical model to predict how roots might change based on temperature. Tey found that 15 percent of root production occurred from January to March, 40 to 45 percent during April and May, and the remaining 40 percent in June, with a high correlation (95 percent) of root growth to rising spring soil temperatures. Based on their model, they suggested that monitoring soil temperature could be used to optimize cultural input timings like water or nutrient applications to enhance use and uptake efficiency.
Question #3. Can tall fescue leaf appearance be modeled based on environmental data? In this experiment (McCarty et al., 1991) researchers wanted to develop a mathematical model to help determine and predict leaf appearance/growth; building on the research
conducted in question #1 (Nelson et al., 1978). Tese scientists wanted to better understand how photoperiod, temperature, plant age, and duration of exposure might be affecting leaf growth. Te researchers’ methods were the following: “plants were observed each day (between 0900 and 1000 hr), the youngest leaf tip was tagged by loosely placing a cloth string attached to a numbered clip at the base of the plant.” Following data collection, a mathematical regression model was developed that predicted (78 percent accuracy) daily leaf appearance using solar radiation, precipitation, soil moisture, maximum/minimum air temperature, and leaf age. Tey also measured soil temperature at 4 inches (10.16 cm) but found that data did not correlate well with leaf appearance. Te authors surmised that this type of model could be used to identify rate limiting steps for leaf growth and/or to implement cultural practices that significantly influence leaf appearance.
What does it all mean? First, not surprisingly, plant growth rates are strongly affected by temperature and increasing temperatures increased leaf and root growth, at least up to an optimal temperature threshold. BUT …there are substantial differences among species and cultivars. If you’ve heard me talk about advances in species and cultivar selection I often mention, “Better ingredients = better lawns.” Now more than ever it’s important to do your homework to select for optimal species/cultivar performance. Data, from cultivar/variety trials by organizations such as the National Turfgrass Evaluation Program (NTEP), for your specific region can be found online (
www.ntep.org).
We are increasingly in an era of niche cultivars and breeders continue to develop and introduce superior cultivars for specific situations based on consumer desires. Secondly, these aforementioned studies helped provide a basis for the development of more data driven decision making tools to optimize turf health. Until next time, be well, be safe, and as autumn approaches, be sure to gently feed your cool-season turfgrasses. Tis will ensure a steady supply of nutrients to help build those all-important carbohydrate reserves.
References:
Nelson, C.J., K.J. Treharne and J.P. Cooper. 1978. Influence of temperature and leaf growth of diverse populations of tall fescue. Crop Sci. 18:217-220.
Koski, A.J., J.R. Street and T.K. Danneberger. 1988. Prediction of Kentucky bluegrass root growth using degree-day accumulation. Crop
Sci. 28:848-850.
McCarty, L.B., J.R. Haun and L.C. Miller. 1991. Daily tall fescue leaf appearance rate in relation to environmental factors. HortSci. 26:114-117.
Cale Bigelow, PhD, is a professor of Turfgrass Science and Ecology in the Department of Horticulture and Landscape Architecture at Purdue University in Indiana. Mike Fidanza, PhD, is a professor of Plant and Soil Science at Pennsylvania State University, Berks Campus. They are teaming to provide a Rooted in Research article for each issue of Turf News.
All graphics courtesy of Cale Bigelow, PhD. TPI Turf News September/October 2022 37
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