The response of grass for silage to sulphur application at 20 sites in Northern Ireland

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Abstract
SUMMARY: Twenty field site3 were selected for their potential sulphur-deficient status. The effect of sulphur at 10 kg S/ha per cut as gypsum or kieserite on the yield and composition of grass for silage given intensive fertilizer was measured at two or three cuts in 1985. Other incidental sulphur inputs in P and K fertilizers and organic manures were minimized. There were significant increases (P < 0·05) in dry-matter yield at ten harvests on five sites. At seven of the ten harvests gypsum and kieserite were equally effective, but at three harvests only kieserite gave significant yield increases. The drymatter yield increases occurred at all three cuts.Using soil analyses to predict sulphur-deficient sites had limited success. The conclusions from this study were that soils with extractable sulphate values < 10 mg S/l had adequate reserves for three-cut silage while soils with values > 10 mg S/l had a 1 in 3 chance of being sulphur deficient. Using plant analyses to diagnose sulphur-deficient herbage had also limited success. In this study herbage with an N/S ratio > 14 was sulphur deficient while herbage with a ratio > 12 had a 1 in 2 chance of being deficient.The proportion of sulphur responsive sites in this study is an overestimate for Northern Ireland as a whole. Most soils in this country have higher clay and organicmatter contents than the field sites. The application of organic manures in normal agricultural practice is likely to be an important source of sulphur to grass for cutting.