ABSTRACT
Estimates of long-term average daily evapotranspiration (ET) and reference evapotranspiration (ETo) have been made for numerous agricultural crops in Puerto Rico [3]. These data are essential for determining monthly irrigation volumes, sizing of pumps and water conveyance devices, and for determining irrigation system fixed and operating costs. Most of the estimates previously made were based on the Soil Conservation Service (USDA-SCS) Blaney-Criddle method [12] and the Hargreaves-Samani method [7]. Harmsen et al. [9] reported large differences between the SCS Blaney-Criddle method [estimates obtained from Goyal, 4] and the Penman-Monteith method in a study that compared seasonal consumptive use for pumpkin and onion at two locations in Puerto Rico. The maximum observed differences were in the order of 100 mm per season. No comparisons have been made between the Hargreaves-Samani [7] and PenmanMonteith methods at locations in Puerto Rico. Inaccurate predictions of ET for an irrigated crop can lead to inefficient use of water and energy, increased potential for surface and groundwater contamination, and reduced profits for the grower.
