2017 ASHS Annual Conference

The production of vegetable crops in the low desert region of the southwestern United States is over a 2 billion dollar industry and product is shipped nationally during the fall-winter-spring period. Many of the alluvial soils used for crop production in the low desert contain low levels of several metals, including cadmium (Cd). There is particular concern about spinach (Spinacia oleracea) which has a propensity to accumulate heavy metals. The large number of spinach samples we collected to date indicate 50% of the spinach produced in the desert would exceed the EU Maximum Levels (ML) of 200 ug/kg fresh weight (FW). Studies have shown soil tests to be potentially useful for predicting Cd accumulation by plants, however, proper sampling protocols and a predictive soil test needs to be calibrated for desert soils. The objectives of these studies was to collect high resolution soil samples from typical production blocks in the desert to assess in-field variability and develop sampling protocols. We also collected paired soil and spinach tissue samples to evaluate the important soil properties affecting Cd concentrations of spinach. The generally low in-field variation and normal distributions of observed values for Cd suggest that a good composite representative soil sample can be collected from the 3 to 10 ha spinach production blocks typically used in the region. While the DPTA Cd soil test was among the best evaluated, it was not sufficiently predictive of spinach Cd concentrations to be utilized as a management tool alone. Data show that in addition to soil test Cd, soil test Zn, soil test P, and soil salinity were correlated to spinach Cd concentrations and need to be incorporated into any soil test algorithm used to predict spinach Cd concentrations.