Seasonal Landscape Crop Coefficients

Amenity landscapes require irrigation during periods of insufficient rainfall.  Significant water use savings may be achieved if landscape irrigation is based on reference evapotranspiration (ETo).  The objective of this study is to determine seasonal landscape crop coefficients (K_L) for model landscapes comprised of turfgrass and woody plant vegetative cover.  The K_L is determined from the ratio of actual evapotranspiration and a modified Penman equation reference.  Irrigation quantity is based on 100% replacement of ETo minus rainfall.  The K_L is determined for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kutze.], yaupon  [Ilex vomitoria ‘Nana’], dwarf Burford holly [Ilex cornuta ‘Burfordii Nana’], and privet [Ligustrum sinense Lour.] combinations, on a Falba fine sandy loam (fine, montmorillonitic, thermic Typic Albaqualfs).  Plant treatments comprised turfgrass/woody plant combinations at 20%/80%, 50%/50%, and 80%/20% vegetative cover.  Soil was systematically placed into lysimeters containing a drainage system and soil moisture probes.  Lysimeters (1586 L) were placed in-ground in a randomized complete-block design with three blocks.  Soil moisture measurements were made at 0 to 20, 20 to 40, and 40 to 60 cm depths.  The K_L was determined after a rainfall or irrigation event for periods of two to five days.  Seasonal differences between early-, mid-, and late-season K_L’s have not been significant.  The K_L’s ranged from 0.8 to 1.1 among the plant treatments across the three growing seasons.