Resistances to evapotranspiration from St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntze) turf

Abstract

A controlled environment study of evapotranspiration from St. Augustinegrass turf, Stenotaphrum secundatum (Walt.) Kuntze, showed that, under well-watered conditions, evapotranspiration was influenced to a greater extent by environmental factors which were external to the plants rather than by stomata. Using the well-known Ohm's Law analogue to define a resistance network for the turfgrass canopy, the magnitudes of the various resistances were measured and compared. Surface resistance, as determined from measurements of diffusive resistance of the leaves and of leaf area index, was found to be one-fourth to one-half the magnitude of the external resistance comprised of the sum of aerodynamic resistance and resistance to air mass exchange within the canopy. It was also found from this study that evapotranspiration increases substantially with days after mowing. The increases in evapotranspiration were attributable to increases in leaf area. The implications of these findings for turfgrass culture are that water use of turfgrasses can be reduced by implementing cultural practices which would restrict excessive leaf area.