Plant water use and crop curves for hybrid poplars

Four years of weekly soil water data measured by neutron probe were analyzed to determine average daily, monthly, and seasonal drip-irrigated hybrid poplar water use. The plantation studied is located near Boardman, Oregon, on the Columbia River Plateau. Irrigation application data, weekly rainfall, and changes in soil water content permitted the construction of a soil water balance model to calculate weekly hybrid poplar water use. Drainage was estimated by calculating potential soil water drainage from the lower soil profile. Sites with the potential for significant drainage were removed from the analysis, so that all sites used in the analysis could be assumed to be at steady state. Crop coefficients were calculated using reference evapotranspiration estimates obtained from a nearby AGRIMET weather station. Crop curves were estimated using a fit-by-hand method similar to that outlined by the United Nations Food and Agriculture Organization. Plant water use estimates and crop curves are presented for one-, two- and three-year-old hybrid poplars. Water use estimates represent upper bound estimates relative to the accuracy of the measurements made.