Five crops, carrot, onion, spinach, cauliflower and lettuce (Daucus carota L., var. sativa D. C.), (Allium cepa L.), (Spinacia oleracea L.), (Brassica oleracea, var. botrytis L.), (Lactuca sativa, var. capitata L.).] were grown successively in pails of virgin sphagnum peat soil receiving 6 rates of Cu and 5 of Mo in a replicated factorial experiment. The soil was limed to slightly above pH 5.0 and other nutrients were added as necessary.
Significant yield responses to Cu applications were obtained with all crops, because of deficiencies on the untreatnts. soil and of toxicities on the plots receiving very high treatments. Molybdenum treatments also encompassed the range from deficiency to toxicity with all crops except spinach.
Except for Cu in onion, analyses for Cu and Mo in aboveground plant tissue after harvests were closely related to treatments. The range in Mo content was 0.2–7, 0.4–42, 0.3–140, 1.8–1,140, and 0.5–280 ppm. for carrot, onion, spinach, cauliflower and lettuce, respectively. The range in Cu content for the same crops was 3.4–14, 6.5–11, 1.6–64, 2.2–17, and 3.1–13 ppm.
A mutual antagonism between Cu and Mo was appaarent whereby the application of one element to the soil significantly affected the content of the other in the plant (except for onion). This was related to a significant yield interaction with cauliflower and to nonsignificant trends with the other crops. In general, the antagonism was exemplified in one or both of the following ways: (i) Toxicities of one nutrient were alleviated by applications of the other; and (ii) deficiencies of one nutrient were aggravated by excesses of the other.