Landscape Coefficients of Newly Planted Mixed- and Single- Species Urban Landscapes.

Urban 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 objectives of this study were to determine landscape crop coefficients (K_L) for landscapes comprised of different vegetation types and to determine if regional climatic differences affect K_L. The K_L was determined from the ratio of actual evapotranspiration and a modified Penman equation reference.   The K_L were determined for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kutze.] alone, Red Oak [Quercus shumardii Buckl.] alone, St. Augustinegrass plus Red Oak, native grasses [Muhlenbergia capillaries (Lam.) Trin. and Schizachyrium scoparium (Michx.) Nash], and native grasses plus Red Oak in College Station and San Antonio Texas, on a Rader fine sandy loam (mixed, semiactive, thermic Aquic Paleustalfs).  Soil was systematically placed into lysimeters containing a drainage system and soil moisture probes.  Lysimeters (1136 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.  During an eight month period in 2007, K_L was greater in San Antonio (0.55) than College Station (0.32).  All interaction effects were not significant except for the season by treatment interaction effect.  The K_L for treatments was similar in spring but in summer, the K_L for native grasses plus Red Oak was greater than for all other treatments except native grasses alone.  In fall, K_L for native grasses plus Red Oak was greater than for all other treatments.  The K_L values in spring, summer, and autumn ranged from 0.26 to 0.44, 0.30 to 0.51, and 0.45 to 0.87, respectively.