Some Effects of Subirrigation on Bentgrass During Heat Stress in the Field

The management of bentgrass (Agrostis spp.) in the southwestern United States presents numerous problems to the grower because of the long period of high summer temperatures associated with this region. Prolonged high temperature stress often results in turfgrass injury from dedication, disease, or insect damage. This study was conducted to determine if the adverse effects of heat stress could be alleviated by subirrigation. A field study was conducted to evaluate the merits of subirrigation on Agrostis palustris Huds. during a 4- month period of heat stress. Effects were evaluated from clipping yields, chlorophyll content and root distribution. Three irrigation treatments were applied to artificial soils of washed mortar sand and a sand-soil mixture. Temperature adversely affected clipping yields and chlorophyll content during excessive heat stress (30 to 35 C) early in the summer. Clipping yields remained low, but color gradually darkened following the initial stress period. Reduction in clipping yields was greater for the mix than sand. Chlorophyll content was not consistently affected by the kind of soil. Sprinkle irrigation and subirrigation from a fluctuating water table resulted in similar yields, whereas subirrigation from a single stable water table at 30 cm produced significantly lower yields. Subirrigated plots also had significantly lower chlorophyll production than sprinkle-irrigated plots. The reduced color associated with subirrigated treatments apparently resulted from poor aeration. Root development was deeper (45 cm vs. 30 cm) and total mass greater in the sand than in the mix. This difference was attributed to a greater % air-filled pore space and lower N levels in the sand. Differences in root mass between irrigation treatments were related to aeration differences in subirrigated plots and N nutrition in surface irrigated treatments. Sprinkler-irrigated plots required periodic syringing while temporary wilting was not observed on subirrigation plots.