Modeling Response of Warm‐Season Turfgrass to Drought and Irrigation

Abstract

When droughts occur, restrictions on outdoor water use are a frequently used tactic for reducing demand but are not always as effective as desired and can have negative impacts on homeowners and businesses. Our objective was to develop a simulation model for use in comparing irrigation strategies in terms of water usage and changes in turfgrass quality under varying levels of water restriction. Based on data from several experiments, we have developed a model for St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] and bermudagrass [Cynodon dactylon (L.) Pers.] that calculates a turfgrass drought index and a turfgrass quality index (TQI) on a daily basis. Turfgrass water demand is modeled as a function of TQI and reference evapotranspiration. Actual turf water uptake depends on plant‐available soil water as well as plant demand. Available soil water in the root zone is divided into two pools: an easily available pool and a less readily available pool. Turfgrass quality can increase when there is no drought stress and decline whenever drought stress exceeds a cultivar‐specific threshold. We used the generalized likelihood uncertainty estimation method to estimate five genetic coefficients for two cultivars of each species. The model was highly successful in predicting the observed values of TQI. Except for a few sample dates, simulated TQI was within the 95% confidence interval of the mean observed TQI. The model appears to respond accurately to both drought and irrigation and to capture species and cultivar differences in drought tolerance.