A crop water stress index for tall fescue (Festuca arundinacea Schreb,) irrigation decision-making -: a traditional method

A high irradiance plant growth chamber was used to study crop water stress indices (CWSI) and baselines with increasing soil water deficit for Tall Fescue (Festuca arundinacea Schreb.). Canopy temperatures for turf plugs were continuously measured with infrared thermometers, along with plant water use, measured with electronic mini-lysimeters. Net radiation, canopy and air temperatures, and vapor pressure deficit (VPD) levels were recorded and analyzed statistically. The canopy-air temperature differential (T-c - T-a) increased with a decrease in soil moisture content. T-c - T-a increased as net radiation became greater, independent of soil water deficit. Canopy temperature of well-watered plants decreased at rate of 2.4 degreesC for each 1 kPa reduction in air vapor pressure deficit for all net radiation levels. For each 100 Wm(-2) increase in net radiation, canopy temperature of well-watered plants increased at a rate of 0.6 degreesC and was well correlated (well-watered baseline) with VPD. Increases in canopy temperature coupled with a decrease in transpiration rate were hallmark signs of water stress progression. However, (T-c - T-a) and VPD baseline relationships correlated poorly for moderate-stress and severe stress conditions regardless of net radiation levels. Thus, even with the increased precision and replications of a controlled environment study, lower limit crop water stress baselines were quite variable. (C) 2001 Elsevier Science B.V. All rights reserved.