Evaluation of the sulphur status of some grasses for silage in Northern Ireland

Seventy-five grass samples for first-cut silage and 131 samples for second-cut silage were collected in 1983 from intensively managed farms with coarse-textured soils. Samples with total sulphur less than 2·0 g/kg or Kjeldahl nitrogen greater than 28 g/kg, together with nitrogen to sulphur ratio greater than 14, and adequate phosphorus and potassium, were selected as suboptimal in sulphur. The extent of sulphur deficiency was assessed using water-soluble sulphate values of 300–500 and 200–300 mg S/kg to indicate yield depressions of less than 5 and 10% respectively. In the first cut, 20 and 8% of sites were likely to have suffered yield depressions of less than 5 and 10% respectively. Soil-extractable sulphate values less than 10 mg S/kg indicated marginal sulphur reserves for second-cut silage at 49% of the sites. Grass analyses of the second-cut samples showed that 11 and 3% of the sites were likely to have suffered yield depressions of less than 5 and 10% respectively. Incidental sulphur inputs from deposition, organic manures and mineralization may have obviated much of the potential sulphur deficiency for second-cut grass.