Evapotranspiration and Leachate Quality of Warm-season Turf and Native Grasses under Different Texas Landscape Climates
Pannkuk, Timothy Richard
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Urban landscapes require irrigation during periods of insufficient rainfall. Significant water use savings may be achieved if landscape irrigation is based on reference evapotranspiration (RET). The objectives of this study were to determine 1.) landscape crop coefficients (K[subscript L]) for landscapes comprised of different vegetation types, 2.) if regional climatic differences affect K[subscript L], and 3.) examine differences in leachate nutrient concentrations from the plant treatments. The K[subscript L] was determined from the ratio of actual evapotranspiration and a modified Penman equation reference. Irrigation quantity was based on 100% replacement of RET. The K[subscript 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 (CS) and San Antonio (SA) 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[subscript L] was determined after a rainfall or irrigation event for periods of two to five days. Leachate was analyzed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium, nitrate-N, orthophosphate-P, and alkalinity. During the growing seasons of 2007 and 2008, K[subscript L] in San Antonio increased from early-, to mid-, to late-season while in CS the K[subscript L] decreased from early-, to mid-, to late-season. Treatments with nativegrasses in SA had K[subscript L]'s as large as 0.91 in late-season. In CS, soil sodium accumulation caused a decreasing seasonal K[subscript L]. Mean DOC concentration was not different between sites except for tree only treatment which was larger in SA. For mean DON concentrations between sites, only the St. Augustinegrass treatment was larger in CS than in SA. Orthophosphate-P concentrations were larger at SA under the tree alone, nativegrass, and St Augustine plus tree treatments than in CS. Ammonium concentration was similar by site for vegetative treatments.