Evapotranspiration of Turfgrass Located Adjacent to a Fallow Desert Soil: A Quantitative Assessment of the ''Edge Effect''

Abstract

A field study was conducted using microlysimeters (ML) to assess the impact of advection on evapotranspiration (ET) of turfgrass in Tucson, AZ. A rectangular block (70 m x 45 m) of irrigated turfgrass [‘Tifway’ bermudagrass (Cynodan dactylon L. x C. transvaalinsis Davy) in summer overseeded in winter with ‘Charger II’ perennial ryegrass (Lolium perenne L.)] was planted in a 1.8 ha fallow agricultural field. Wind flow at the site was typically parallel to the long dimension of the block and decidedly periodic due to a mountain-valley flow regime. Parallel rows of ML were installed in the turf at varying distances from the two edges of the field subjected to advection. ET along the edge of the field subjected to afternoon advection averaged 10.8 and 8.2% higher than ET in the middle of the field in summer and winter, respectively. Enhancement of ET relative to the field middle was smaller for the turf edge subjected to evening and morning advection and averaged 6.8% in summer and 4.7% in winter. ET from MLs located 7 m from the edge of the field were typically within 5% of ET measured in the field middle, indicating the impact of advection diminishes rapidly with distance. A simple advective index computed from wind speed and vapor pressure deficit may prove useful in quantifying the impacts of advection. Introduction Turfgrass planted in many Desert Southwest environments is vulnerable to advection of sensible heat from adjacent hot, dry surfaces. Advection serves as an additional source of energy and should accelerate evapotranspiration (ET) along the perimeter of turfed areas. Turf managers believe advection is responsible for a condition referred to as the “edge effect” – strips along the perimeter of turfed areas that are difficult to keep moist and exhibit poor turf quality. While the relationship between advection and the edge effect are accepted by many in the turf industry, there is Copyright ASCE 2005 EWRI 2005 surprisingly little quantitative data describing the magnitude and spatial impact of advection on turfgrass ET. The study described in this paper represents an initial effort to quantify the impact of advection on ET from desert turfgrass systems. Materials & Methods The study was conducted in a 1.8 ha fallow agricultural field located at an elevation of 714 m in Tucson AZ. A rectangular area of turf measuring 69 m length (east-west dimension) and 46m in width (north-south dimension) was established in the middle of the field (Figure 1) with the remaining field area maintained in a fallow condition. Wind flow at the site was decidedly periodic (Brown et al., 1995) with upriver/up slope (from west to east) flow during the day and down river/downslope at night (from east to west). The distance of fallow fetch on both the east and west sides of the field was greater than 60 m. Figure 1. Plan vie and the black cir maintained in a fal Turf consisted of Davy) in summer winter. The turf fertilized once a m rate of 73kg/ha. irrigation heads se treated effluent se except during peri in evaporative dem P1.3 P1.6 Copyright ASCE 2005 w of the field site. The green (shaded) area represents the turf area cles indicate ML locations. The area surrounding the turf was low condition. Tifway bermudagrass (Cynodon dactylon L. x C. Transvaalinsis and overseeded Charger II perennial ryegrass (Lolium perenne L.)in was mowed 2-3 times per week at a height of 1.6 cm and was onth by applying granular commercial fertilizer (21N,7P,14K) at a Irrigation was supplied to the turf using 12 Rainbird Series 900 t in a square pattern with head separation equal to 23 m. Tertiary rved as the water source for irrigation. Irrigation was applied daily ods of rainfall with rate adjusted regularly to meet seasonal changes and (Brown, 2000). W E S T