Seasonal and Species Variation in Baseline Functions for Determining Crop Water Stress Indices in Turfgrass

Abstract

Empirically based relationships between canopy minus air temperature (Tc–Ta) regressed on vapor pressure deficit (VPD) have been described as measures of crop water stress indices (CWSI) and indicators for irrigation scheduling. This study was conducted to determine seasonal and turfgrass species variation in empirical‐baseline functions. Empirical and energy‐balance CWSI functions also were compared to determine which was the most accurate estimate of CWSI over the range of turfgrass species and conditions studied. Field experiments were conducted to compare CWSI relationships derived during different climatic seasons and four different turfgrass species: buffalograss, Buchloë dactyloides (Nutt.) Engelm. cv. Texoka; common bermudagrass, Cynodon dactylon (L.) Pers. cv. Arizona common; St. Augustinegrass Stenotaphrum secundatum (Walter) Kuntze cv. Raleigh; and, tall fescue Festuca arundinacea Schreber cv. Falcon. Data were collected in midsummer of 1986 and late summer of 1987 from plots irrigated with a linear‐gradient irrigation system. The CWSI relationships were calculated from the two lowest canopy temperatures in each plot during 7 July to 1 Aug. 1986 and 30 Aug. to 11 Sept. 1987. Differences between CWSI baseline functions from 1986 and 1987 for common bermudagrass, buffalograss, and tall fescue were highly significant (P < 0.01). Mean values of net radiation, VPD, and wind speed also were significantly different (P < 0.01) for the seasons. Vapor pressure deficit usually accounted for more than 50% of the variability in Tc–Ta across seasons and turfgrass species. Using the energy‐balance method to calculate CWSI and comparing these values with empirical calculated CWSI values reduced the portion of index differences that were greater than 0.1.

Models for Predicting the Lower Limit of the Canopy‐Air Temperature Difference of Two Cool Season Grasses

“…The results of this research concur with those of Horst et al (1989) and Smith et al (1986), which indicate that more complex models are necessary for accurate prediction of (T c -T.)LL in areas where WS, VPD, and R n are highly variable. Based on work perfonned on an independent data set, Smith et al (1986) found the complete energy-balance approach with r. and I"c as dynamic components to be more satisfactory in predicting T c -T. of nonwater-stressed wheat (Tliticum aestivum L. emend.…”

“…A general model applied across Kentucky bluegrass and creeping bentgrass in this study introduced bias when used on creeping bentgrass, possibly indicating that a separate model was necessary on creeping bentgrass. Work by Horst et al (1989) suggested that baselines used in an empirical approach to CWSI calculation were likely species x cultural regime x seasonal condition specific. Further testing of the models developed in this study at different locations on various grasses managed under different cultural regimes could provide more information on the limitations of the empirical approach to CWSI calculation on turfgrass.…”

Soil‐water‐use Characteristics of Precision‐irrigated Buffalograss and Kentucky Bluegrass

“…The resulting regression model was used to predict well‐watered turf T L ‐T A at a given VPD for comparison against T L ‐T A values under water‐stressed conditions after we initiated dry‐down treatments. This formulation is similar to the simplified version of the crop‐water‐stress index (13), which was previously applied to turfgrass (11).…”

“…Leaf canopy temperature offers a relatively clear and easily determined signal of water stress because when stomata close, transpirational cooling decreases and leaf canopy temperature increases relative to air temperature (13). Using leaf canopy temperature to detect water stress for irrigation has been applied to turfgrass in other studies (11,17).…”

Performance of Three Warm Season Turfgrasses under Linear Gradient Irrigation

“…Irrigation was applied twice weekly at a rate of 120% of reference evapotranspiration (ET 0 ) accumulated since the previous irrigation event. The 120% ET 0 kept the soil nearest the line close to field capacity (Horst et al, 1989;Qian and Engelke, 1999), and the portion of the plot farthest from the centre line received no supplemental irrigation. Efforts were made to irrigate only when wind was minimal.…”