THE EFFECT OF SULPHUR NITROGEN/SELENIUM INTERACTIONS ON HERBAGE YIELDAND QUALITY/

The objectives of the study were to examine (1) the effects of sulphur , at various levels of nitrogen fertiliser, on herbage yield and quali ty and (2) the effects of S fertiliser on the uptake of selenium by he rbage. Results are presented from two field experiments, one at Borris okane, Co. Tipperary, where four cuts of herbage were taken during the season, and the other at Screen Co. Wexford, which involved grazing b y Friesian steers. The cutting trial showed that S fertiliser increase d herbage yield at both high and low levels of N application. When N w as applied at 480 kg/ha without S the yield achieved was 60% of that o btained when both elements were applied. It was shown, that S fertilis ation enabled a chosen level of herbage production to be maintained at lower rates of N fertiliser. S also improved the quality of the herba ge and this was reflected in lower nitrate-N and higher protein-N cont ent. The uptake of native and soil-applied Se by herbage was reduced b y S fertilisation, particularly in late season. Se uptake by herbage i n the grazing experiment was also reduced by S fertiliser and, in autu mn, the blood Se status of the cattle grazing the S-treated area was s ignificantly lower than for cattle grazing herbage on the area which w as not treated with S fertiliser.