Seasonal changes in the concentrations of copper, molybdenum and sulfur in pasture plants

Abstract

Seasonal changes in the concentrations of copper, molybdenum and sulfur in subterranean clover (Trifolium subterraneum), silver grass (Vulpia sp.), Wimmera ryegrass (Lolium rigidum), and capeweed (Arctotheca calendula) growing on lateritic podzolic soils were measured in glasshouse and field studies. The effects of varying soil temperature and water content on the concentrations of copper, molybdenum and sulfur in subterranean clover on a lateritic podzolic soil and a calcareous sand were also investigated. Similar seasonal patterns in plant composition were observed in the glasshouse and the field. The concentration of molybdenum tended to remain constant throughout the season, but that of copper and sulfur declined from autumn to spring; the decline was more rapid in the grasses than in subterranean clover and capeweed. Subterranean clover had higher concentrations of copper and sulfur but lower molybdenum than silver grass or Wimmera ryegrass. Capeweed contained more copper and molybdenum but less sulfur than subterranean clover. The concentrations of molybdenum and sulfur were similar in capeweed and the grasses. lncreasing soil temperature from 12 to 22¦C increased the dry matter production and the concentrations of copper and molybdenum (but not sulfur) in subterranean clover on both soils. lncreasing soil water content slightly increased dry matter production and the concentration of molybdenum but had no effect on the concentration of copper and sulfur in subterranean clover. The results are discussed in relation to the health of grazing animals.