Differential Response of Zoysiagrass Genotypes to Soil Moisture.

Four water table depth gradient tanks were utilized at the Crop and Soil Sciences greenhouse complex at the University of Georgia in 2015/2016 to evaluate the response of experimental zoysiagrass genotypes to soil moisture. Each tank was steeply sloped and had a volume of nearly 0.9 m³. Tanks 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 lined with 3 mm plastic and had a 10 cm base of pea gravel that provided a uniform substrate for water movement. 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 regulated 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). Soil moisture measurements were taken at each level and averaged across tanks to determine capillary fringe. One year old ’09-TZ-53-20’, ’09-TZ-54-9’, ’10-TZ-35’, and 'Zeon' zoysiagrass sod (0.3 m wide) were established on the soil surface of all four tanks and allowed to grow-in for two months prior to soil moisture treatment initiation. Normalized difference vegetation index (NDVI) was recorded weekly to determine plant health/turfgrass quality. Lowest order curves giving high R² values were fit to data for comparison of zoysiagrass genotypes at different soil moisture levels. Two months after trial initiation, all zoysiagrass genotypes declined with respect to NDVI measurement as DWT increased from level 1 to level 9. All zoysiagrass genotypes exhibited similar NDVI readings at level 1 (0.76 to 0.78) and level 2 (0.73 to 0.77). At level 3 and 4, 09-TZ-53-20 exhibited the lowest NDVI when compared to the other genotypes. At level 5, NDVI readings for all genotypes were ≤ 0.22, with 09-TZ-54-9 and 10-TZ-35 resulting in the highest readings (0.19 and 0.22, respectively). At level 6, 10-TZ-35 resulted in the highest NDVI reading (0.16), while all other genotypes exhibited NDVI readings ≤ 0.07. At levels 7 through 9, all experimental zoysiagrass genotypes were still alive, while Zeon exhibited an NDVI of 0.02 at level 7 and was completely desiccated at levels 8 and 9 (NDVI = 0.0). Higher NDVI readings and plant survival exhibited by experimental genotypes grown at the drier levels of the gradient tanks compared to Zeon (industry standard) indicates improved drought stress tolerance.