Sulfur nutrition of temperate pasture species. II. A comparison of subterranean clover cultivars, medics and grasses

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Abstract
The external and internal requirements for sulfur of five pasture legumes and three grasses of temperate origin were examined in a pot experiment in which plants were grown with seven levels of sulfur supply for 58 days. Nitrogen supply was non-limiting. There was no distinct difference between legumes and grasses in their external requirement for sulfur (i.e. the amount of sulfur required for 90% of maximum yield) or in their sensitivity to sulfur deficiency (i.e. yield at the lowest sulfur supply expressed as a percentage of maximum yield). The requirement for sulfur (mg/pot) fell in the following order: Hunter River lucerne (24) > Jemalong barrel medic (19) > brome grass and Wimmera ryegrass (18) > barley grass (15) > Clare subterranean clover (13) > Trikkala subterranean clover (11) > Seaton Park subterranean clover (10). The high external requirement for sulfur of Hunter River lucerne appears to be due to its poor ability to distribute sulfur from root to shoot and to its high internal requirement for sulfur. However, for Jemalong barrel medic, the high external requirement was solely due to its high internal requirement for sulfur. The higher external requirement for sulfur of the grasses compared with the subterranean clover cultivars appears to be due to the poorer ability of the grasses to obtain sulfur from the soil used in this experiment, rather than to differences in the transfer of sulfur from root to shoot, or in their internal requirement for sulfur.