The effects of cobalt additions on soil and herbage cobalt concentrations in some S.E. Scotland pastures

SUMMARY Cobalt, as cobalt sulphate and cobalt-EDTA, was applied to pastures at 15 sites in south-east Scotland. Herbage cobalt and extractable soil cobalt concentrations were monitored at these sites over the period 1978–81. Although the sites were located in a generally cobalt-deficient area, considerable variation between sites was observed both in the concentration of cobalt present in untreated pasture and in the response to cobalt additions. There was no significant correlation between herbage cobalt concentrations and soil cobalt status as determined by acetic acid extraction. Application of cobalt sulphate (6 kg/ha) increased herbage cobalt concentrations at all sites but at several sites the response was short-lived. In general, cobalt-EDTA was less effective than cobalt sulphate in increasing herbage cobalt concentrations. Extractable soil cobalt concentrations of the control areas showed some variability between samplings, but the variability was much greater for the cobalt-treated plots. Cobalt applied to pastures was found to accumulate in the top 0–4 cm layer of soil and penetrated deeper only in soils of low pH. Overall, only a third of the cobalt applied to pastures as cobalt sulphate was recovered by acetic acid extraction of the soil and less than 20% of the cobalt applied as cobalt-EDTA.