The effects of soil properties on the availability of cobalt (Co) for pasture uptake have been studied using a wide range of New Zealand soils. There is a strong positive correlation between total or EDTA-extractable Co and manganese (Mn) concentration. However glasshouse studies have shown that Co availability is inversely related to the Mn concentration. Across a wide range of soil groups, EDTA-extractable Co is a poor predictor of cobalt availability. CaCl₂-extractable Co was found to decrease with soil pH and was too pH sensitive to be a good predictor of Co availability. It is concluded that soil Mn plays a crucial role in soil Co status and has significant effects on plant Co uptake because of its involvement in the soil redox system and the scavenging properties of soil Mn oxides. Co deficiency is more likely to occur and Co fertiliser is less effective on soils with high Mn, especially under dry conditions.