Viability of Deficit Irrigation Using Historical Average Reference Evapotranspiration.

Crop coefficients have been previously developed for warm-season turfgrasses under a variety of stress levels.  Data which quantify turf performance under described crop coefficient stress levels are not as readily available.  Crop coefficient-based irrigation programs can be difficult for residential lawn managers because of the need for real-time meteorological data.  A field study was initiated in 2011 to imitate a residential lawn managed for summer seasonal deficit irrigation based on historical average reference evapotranspiration (ETo).  The study was conducted on St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze ‘Raleigh’] turf mowed at a height of 64 mm.  The soil was a Booneville fine sandy loam (Fine, smectitic, thermic Chromic Vertic Albaqualfs) having a particle size distribution 0.7 g g^-1, 0.2 g g^-1, and 0.1 g g^-1 sand, silt, and clay respectively.  The experimental design was a randomized complete block split-split-plot arrangement having whole main irrigation plots split by fertility level and wetting agent treatments.  Irrigation scheduling was initiated on July 1, 2011, to apply the following irrigation treatments three days per week (MWF): ‘overwatering’ (100% ETo), ‘turf coefficient’ or ‘Tc’ (60% ETo), ‘normal stress’ (60% Tc), ‘severe stress’ (40% Tc). 

Preliminary results have affirmed the robustness of the turf coefficient (0.6) during the worst one year drought in Texas history (2011).  Additionally, normal stress deficit treatment provided adequate green cover for regrowth during autumn and spring when precipitation was more prevalent.  In residential areas where modest quality loss is acceptable, deficit irrigation using historical averages appears to effectively conserve water while maintaining source plant material for eventual recovery.  Additional data (e.g., soil moisture, clipping yield, digital image analysis) will be discussed.