Influence of Plant Part on Nitrate Concentration in Lettuce and Spinach

The concentration of nitrate-nitrogen (NO3-N) varies between lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.). Nitrate is potentially harmful if consumed in large amounts by humans; therefore, understanding which cultivars and plant parts concentrate NO3-N can be useful in developing approaches to reduce dietary NO3-N intake. We determined NO3-N concentration and distribution in cultivars of field-grown lettuce and spinach. In 2006, NO3-N concentration was highest in the outer leaf whorl and lowest in the center of spinach; no difference was found in lettuce. In 2007, overall soil and tissue NO3-N concentrations were lower and there was no interaction between plant part and species or cultivar and no difference among leaf whorls; all cultivars had higher NO3-N concentrations in the midrib and petiole than in the leaf. Differences in NO3-N concentration and distribution suggest that practices such as cultivar selection and selective removal of high NO3-N parts can lower NO3-N consumption by humans.