Response of Bermudagrass and Zoysiagrass to a Soil Moisture Gradient and Mowing Height.

Four water table depth gradient tanks were constructed at the Crop and Soil Sciences greenhouse complex at the University of Georgia in 2013 to evaluate the response of turfgrass to soil moisture and mowing height. Each tank was steeply sloped and has a volume of nearly 0.9 m³. Tanks were oriented to the south and measured 2.4 m long, 1.2 m wide, and were 0.3 m high at one end and 1.8 m high at the other end. Tanks were filled with a 2:1 mixture of a Pacolet sandy clay loam (fine, kaolinitic, thermic Typic Kanhapludults) and course sand. A valve at the high end of the tank regulated water inflow, while a standpipe at the low end of the tank regulated the water table height. Tank surfaces were divided into 9 levels ranging in depth to the water table (DWT) of 27 cm (level 1) to 151 cm (level 9). One year old ‘Tifway 419’ hybrid bermudagrass and 'Zeon' zoysiagrass sod were established on the soil surface of two tanks, respectively and allowed to grow-in for three months. One side of each tank was maintained at 2.5 cm and the other at 5.1 cm. Turfgrass quality ratings, normalized difference vegetation index (NDVI), and canopy temperature was evaluated throughout the study. Cores (10.2 cm in diameter) (3 per level) were removed at trial termination (90 days after initiation) to determine root biomass. Zoysiagrass maintained turfgrass quality above acceptable levels (> 6.0) for levels 1 through 3 at the 5.1-cm mowing height and levels 1 and 2 for the 2.5-cm mowing height. Although turfgrass quality was significantly below acceptable levels when zoysiagrass was subjected to drought (levels 7 through 9), increasing mowing height from 2.5 to 5.1 cm did have a positive impact. A similar trend was observed with respect to NDVI. Zoysiagrass root biomass was similar for both mowing heights under sufficient soil moisture conditions, but more root mass was observed in response to the 5.1-cm mowing height when zoysiagrass was subjected to drought (levels 7 through 9) compared to the 2.5-cm mowing height. Turfgrass canopy temperature increased as soil moisture levels decreased. However, mowing height had no effect on canopy temperature. Canopy temperature of zoysiagrass was 22.2 to 23.9 °C for levels 1 and 2, 25.5 to 26.7 °C for levels 3 through 6, and 28.3 to 30 °C for levels 7 through 9. Bermudagrass did not exhibit turfgrass quality above acceptable levels for any soil moisture level, regardless of mowing height. However, bermudagrass turfgrass quality was less affected by drought (levels 7 through 9) than zoysiagrass, regardless of mowing height. A similar trend was observed with respect to NDVI. Bermudagrass root biomass was greater when plants were mowed at 5.1 cm compared to 2.5 cm. However, when subjected to drought (levels 7 through 9), root biomass in response to both mowing heights was similar. This trend was opposite of what was observed in gradient tanks containing zoysiagrass. Bermudagrass was also able to maintain lower canopy temperatures (26.7 to 27.8 °C) than zoysiagrass (28.3 to 30 °C) at low soil moisture (levels 7 through 9).