2019 ASHS Annual Conference

Water and salt management are of paramount importance to agricultural sustainability of vegetable crop production systems in the lower Colorado River region. Salinity of the available irrigation water coupled with capillary rise from slightly saline shallow ground water sources in the valleys can result in surface salinization. Maintaining acceptable root zone salinity levels requires some level of excess irrigation (beyond crop consumptive use) to leach salts below the crop root zone. A prerequisite to the utilization of leaching as a management tool is effective internal and external drainage. Salt sensitive cool season vegetables are planted from September through January and harvested from November through April each year. Studies were conducted from 2016 to 2019 to quantify water and salt balance in these production systems. Crop water use, represented by evapotranspiration (ET) was estimated using eddy covariance systems. Amounts of water applied by sprinklers was measured by automated gauges. Water measured by in-flow hydrographs was used to quantify water applied by surface irrigation. Soil salinity was monitored by electromagnetic (EM 38, Geonics Ltd., Mississauga, Canada) surveys and augmented by soil samples. The salinity in water and soils extracts was measured by conductance and the cations and anions measured by ion chromatography. Results show irrigation application efficiencies during the vegetable production period are high (>90%) and the required leaching is not achieved during the vegetable production period. Often the water management of the rotational crops in the spring and summer (wheat, Sudan grass, melons) do not result in the required leaching and a pre-irrigation before the cool season vegetable cycle begins is required for sustainability.