Water use and estimated evapotranspiration at a California container plant nursery

The objective was to investigate water use per area and its relationship to reference evapotranspiration (ET_O) at a large-scale container-grown plant nursery in California. Monthly applied irrigation was recorded during 2016 and 2017. Irrigation runoff was captured and measured from impervious material-lined production areas and runoff channels. A runoff coefficient for irrigation volume was developed for periods absent of precipitation. For periods when runoff volume data did not exist, estimated runoff volume was determined by multiplying the runoff coefficient by applied irrigation volume. Estimated runoff volume was subtracted from total applied irrigation volume to estimate total nursery water use. Total nursery water use was divided by the nursery production area to estimate nursery evapotranspiration (ET_N). Monthly ET_o was recorded from two California Irrigation Management Information System (CIMIS) stations, #44 and #240, 19 km and 17 km from the nursery site, respectively. A monthly nursery coefficient (K_N) was derived by dividing monthly ET_O by monthly ET_N, a similar calculation to crop coefficient (K_c). Monthly non-recovered irrigation volume ranged from 6,304 to 69,832 m³ with a mean of 32,066 m³ during 2016-2017. Monthly non-recovered irrigation volume was greater during periods of higher ET_O. Estimated monthly K_N at the nursery was 0.21 to 0.56. Although runoff conduits were lined with impervious material, infiltration and evaporation did occur and accounting for those losses would further reduce K_N.