In the technique presented,35S was used to label the soil available sulfur pool in intact pasture cores, which were subsequently treated with different sulfur fertilizers. Dilution of the35S in the soil by sulfur released from the fertilizers was monitored by measuring the changes in specific radioactivity of sulfur in plants growing in the cores. The results showed the effects of fertilizer form, particle size and application rate on the supply of sulfur to plants. This technique will be useful for making direct comparisons of the ability of commercially available fertilizers to maintain the supply of sulfur to plants.