New Zealand Journal of Agricultural Research abstracts

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Cadmium cycling in sheep-grazed hill-country pastures

A. H. C. Roberts*
R. D. Longhurst

AgResearch Land and Environmental
Management Group
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
*Present address: Ravensdown Fertiliser Co-operative, P.O. Box 608, Pukekohe, New Zealand. Email: ants.roberts@ravensdown.co.nz

Abstract  Cadmium (Cd) cycling in a sheep-grazed hill-country farming system was investigated to determine the important factors influencing accumulation in edible sheep tissues. A farmlet-scale trial was established consisting of a total of 10 paddocks that had a history of 15 years of 5 different rates of phosphatic (P) fertiliser applications. The trial comprised 2 flocks of Romney ewes managed at 2 different grazing pressures. Each flock was rotationally grazed over 1 block of 5 paddocks, each of which represented a different rate of P (10, 20, 30, 50, and 100 kg P ha^–1). Over a 4-year period, the trial investigated seasonal variation of soil and herbage Cd; effect of rate of P and paddock stratum (sheep campsites, tracks, easy, or steep slopes) on soil and herbage Cd; and pasture intake or soil ingestion as possible modes of Cd entry into the grazing animal. Annual Cd liver and kidney tissue accumulation rates in ewes between 18 and 66 months of age were estimated at 19 and 43%, respectively, but were unaffected by grazing intensity. Soil ingestion contributed only 3–6% of total Cd ingestion by grazing sheep. The remainder arose from the pasture diet of the sheep and points to the need to reduce further Cd inputs to soils and minimise the uptake by plants of Cd already present.

Keywords  cadmium cycling; hill country; pastures; phosphatic fertiliser; soil ingestion

A01017 Received 21 June 2001; accepted 23 January 2002
New Zealand Journal of Agricultural Research, 2002, Vol. 45: 103–112
0028–8233/02/4502–0103 $7.00/0 © The Royal Society of New Zealand 2002

PDF file of entire paper: Print-quality (191K)

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