Critical nitrate levels for leaf lettuce, radish, and spinach plants

Abstract

Leaf lettuce (Lactuca sativa var. crispa L.), radish (Raphanus sativus L.), and spinach (Spinacea oleracea L.) plants were grown in sand culture under variable N concentrations from 0.187 to 48.0 meq/l. The plants were harvested when those grown at 12 meq N/l had attained approximate market maturity. Growth was restricted, and symptoms of N deficiency were evident at the low levels of N. Growth was also restricted at the highest N level. Approximate critical levels for leaf lettuce, radish roots, and spinach are 2000 ppm, 5000 ppm, and 4000 ppm, nitrate‐N respectively, on a dry weight basis.