Fertilisers are usually evaluated by their effects on herbage DM yield and occasionally herbage composition. Rarely are the effects on animal production considered, even though there is evidence for example that increasing the sodium (Na) contents of herbage can increase the milk yield of dairy cows (Chiy and Phillips, 1991), and that dietary sulphur (S) contents in excess of l-2g/kg DM will lead to reduced intake and productivity in ruminants (Raisbeck, 1982). In the UK the use of sulphur fertilizer is widely advocated, since herbage growth is often restricted by deficiency now that industrial emissions have been reduced. Sulphur fertilizer increases herbage S content, but Na fertilizers can affect herbage S content and S utilization by ruminants (Chiy et al., 1994). The effects of Na and S fertilizers were therefore studied with particular emphasis on herbage composition and dairy cow production.