Creeping bentgrass (Agrostis palustris Huds.) is used on putting greens for its fine-leaf texture, consistent speed, smooth ball roll, and year-round color. In recent years bentgrass use has extended into the warmer climates of the southern United States. Being a C3 plant, bentgrass is not well adapted to extended hot and humid environmental conditions. Subsurface air movement systems are now commercially available that can transport air through the root zone to alter soil conditions and potentially improve bentgrass survival. This research investigated the effects of subsurface air movement on the composition of soil gases, matric potential, temperature, and growth response of a sand-based creeping bentgrass golf green. Treatments included: air movement direction (evacuate, inject, and no air) and duration of air movement (0400-0600 hr, 1000-1800 hr, and 24 hours). Treatment combinations were imposed for 13 days. Subsurface air movement reduced CO2 at the 9-cm depth to values <0.0033 mol·mol-1 when evacuating or injecting air, depending upon duration. Soil matric potentials at a 9-cm depth were decreased by a maximum of 96% when evacuating air for 24-hour duration compared to no-air plots. Soil temperatures at 9 cm were decreased ≈1 to 1.5 °C when injecting air from 1000 to 1800 hr and 24-hour treatments and increased ≈0.75 °C when evacuating air from 1000 to 1800 hr. Subsurface air movement did not improve creeping bentgrass turf quality or rooting. Although not effective in improving the growth response of creeping bentgrass, subsurface air movement may be a useful tool to improve soil gas composition, reduce excess soil moisture, and potentially reduce soil temperature(s) of heat-stressed creeping bentgrass golf greens.
B. Todd Bunnell, Lambert B. McCarty, and Hoke S. Hill
Timothy L. Grey, Mark Czarnota, Thomas Potter, and B. Todd Bunnell
Flurprimidol is a plant growth regulator that can be applied as a granular formulation. Understanding flurprimidol release from a granular formulation and movement in various mediums will impact how it is used. Dissipation of flurprimidol from a granular formulation and movement through organic media and sand were evaluated in a greenhouse and laboratory experiment. Experimental variables included media type, depth, and irrigation event. Dissipation isotherms were determined by applying nonlinear regression. Mobility was evaluated using columns filled with media, which was surface-spiked with the granular formulation and then irrigated once daily for 22 consecutive days. Leachate was collected and analyzed by high-performance liquid chromatography–mass spectroscopy. Half-life (DT50), defined as time to 50% reduction, varied among sand, media, and media depth. Flurprimidol dissipation was rapid through sand with DT50 of 6 days. DT50 increased with increasing media depth from 5 to 10 cm for pine bark plus sand, 18 and 35 days, and hardwood bark plus sand, 77 and 173 days, respectively. Maximum flurprimidol leaching was a cumulative 71% of applied amounts over 22 irrigation events through the sand. Hardwood and pine bark media allowed less than 25% of flurprimidol to escape through the column. Data for all media indicated that flurprimidol was mobile through the substrates but exhibited hysteresis with pine bark and hard wood bark media. An initial pulse of flurprimidol will release slowly from this formulation over time. These results indicate that flurprimidol will dissipate from a granular formulation over time and that it will have movement through sand soil and pine bark and hardwood bark media to reach the roots of growing plants.
B. Todd Bunnell, Lambert B. McCarty, Roy B. Dodd, Hoke S. Hill, and James J. Camberato
Increased soil moisture and temperature along with increased soil microbial and root activity during summer months elevate soil CO2 levels. Although previous research has demonstrated negative effects of high soil CO2 on growth of some plants, little is known concerning the impact high CO2 levels on creeping bentgrass (Agrostis palustris Huds.). The objective of this study was to investigate effects of varying levels of CO2 on the growth of creeping bentgrass. Growth cells were constructed to U.S. Golf Association (USGA) greens specification and creeping bentgrass was grown in the greenhouse. Three different levels of CO2 (2.5%, 5.0%, and 10.0%) were injected (for 1 minute every 2 hours) into the growth cells at a rate of 550 cm3·min-1. An untreated check, which did not have a gas mixture injected, maintained a CO2 concentration <1%. Gas injection occurred for 20 days to represent a run. Two runs were performed during the summer of 1999 on different growth cells. Visual turf quality ratings, encompassing turf color, health, density, and uniformity, were evaluated every 4 days on a 1-9 scale, with 9 = best turf and <7 being unacceptable. Soil cores were taken at the end of each run. Roots were separated from soil to measure root depth and mass. Turf quality was reduced to unacceptable levels with 10% CO2, but was unaffected at lower levels over the 20-day treatment period. Soil CO2 ≥2.5% reduced root mass and depth by 40% and 10%, respectively.