Effects of long-term and short-term cattle grazing on heavy metals concentrations in tropical pastures of Malaysia

This study investigates the impact of cattle grazing intensity at long-term (LT, 2.7 AU/ha/y for 33 years) and short-term heavy (ST, 5 AU/ha/y for 2 years) on the heavy metal concentrations in soils of tropical pastures, Malaysia. Soil samples were collected at randomly selected points at 0-10 and 10-20 cm depth in both grazed and ungrazed treatments. The concentration of heavy metals (Cd, Fe, Mn, Cu, Cr, Pb, and Zn) was measured by inductively coupled plasma (ICP) spectrophotometry. The heavy metal concentrations in the soil were not affected by ST grazing intensity. The concentrations of Fe, Mn and Zn were significantly affected (P £ 0.05) by LT grazing intensity. The concentrations of Fe, Mn, Cu and Zn in LT grazed pasture soil were 127.9, 194.8, 54.8 and 39900% higher, respectively, than ungrazed pasture. Soil Fe, Mn and Zn concentrations were significantly higher (P < 0.05) in surface (0-10 cm) than subsurface (10-20 cm) soils. Results suggest that the excreta of grazing cattle can be an important source of heavy metals in intensively managed pastures in the long-term. However, metal concentrations were maintained below the maximum standard limits and were not high enough to be dangerous from the toxicological point of view.