Evaluation of Atmometers within Urban Home Lawn Microclimates

Abstract

ABSTRACTAn atmometer is an inexpensive tool used to measure evapotranspiration (ET) in situ. The effects of microclimates associated with urban lawns on the performance of atmometers are not well documented. Our objective was to compare ET estimates between atmometers and the FAO‐56 Penman–Monteith equation (PMET, FAO56‐PM), including within urban lawns. The study was conducted in six lawns in 2010 and one in 2011 in Manhattan, KS, and four lawns in Wichita, KS, in 2011. A weather station and atmometer were positioned in an open sward of turfgrass near each city during each measurement period in Manhattan and Wichita. A commercially available Bellani plate atmometer, using a green canvas cover for grass reference ET (ATET), was placed next to a portable weather station in two contrasting microclimates within each lawn. Weather stations recorded temperature, net radiation, relative humidity, and wind speed data used to calculate PMET. Open sward ATET (4.73 mm d–1) averaged 14% less than PMET (5.48 mm d–1). Within microclimates, ATET (3.94mm d–1) averaged 22% greater than PMET (3.23 mm d–1). The differences in ET estimates between measurement techniques varied with wind speed, net radiation, and vapor pressure deficit. The best relationships between ATET and PMET, at the open sward and within microclimates, occurred when wind speed was >1 m s–1, vapor pressure deficit was >2 kPa, and net radiation was >5 MJ m–2 d–1. Overall, atmometers can provide reliable estimates of PMET and could benefit practitioners with irrigation management within microclimates.