Molybdenum and Copper Uptake by Forage Grasses and Legumes Grown on a Metal‐Contaminated Sludge Site

Abstract

Wastes applied to agricultural land can contain significant concentrations of bioavailable molybdenum (Mo). Because Mo uptake by forage crops could lead to hypocuprosis in ruminants, more knowledge is needed about which crops are most efficient in accumulating Mo. At an old sewage sludge‐amended site, the concentrations of Mo, copper (Cu), and several other trace metals were measured in various grass species. Generally, the grasses grown on the sludge site contained higher Mo concentrations than the same species grown on a nearby control site. However, because Cu concentrations were also higher in the sludge‐grown grasses, Cu:Mo ratios in the grasses were frequently higher on the sludge site. In contrast, all legumes tested (alfalfa, birdsfoot trefoil, red clover, pea), as well as canola and beets, had lower Cu:Mo ratios when grown on the sludge site. Sulfur concentrations in the two crops analyzed for this element (canola and pea) were higher on the sludge site than the control. It is concluded that Mo, Cu, and sulfur (S) bioavailability remains elevated in the soil several decades after sewage sludge application.

Keywords:

• Molybdenum
• copper
• sulfur
• sewage sludge
• biosolids
• forage legumes
• grasses
• heavy metal uptake
• bioavailability
• soils

Acknowledgment

This research was supported by the USDA Agricultural Ecosystems Program, Award No. 91‐34244‐5917.