Some effects of lime, nitrogen and soluble and insoluble phosphate on the yield and mineral composition of established grassland

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Abstract
Summary: Twelve factorial experiments made from 1977 to 1981 compared the effects of 0, 4 and 8 t CaCO3/ha, 0 and 360 kg N/ha/year as urea and 0 and 60 kg P/ha/year as either superphosphate or ground rock phosphate on the yield and mineral composition of established grassland on soils of pH 4·7–5·6 in Northern Ireland.Lime did not increase yield whether urea was applied or not. It substantially reduced herbage Mn and, to a lesser extent, herbage P, Mg and Zn.With lime, ground rock phosphate was almost completely ineffective in raising yield and herbage P content. Without lime, it had some value but was less effective than superphosphate.Soil P extracted either by ammonium acetate at pH 4·2 or Olsen sodium bicarbonate reagent did not predict response to superphosphate. When the soil test values were adjusted for field bulk density, soil P extracted by ammonium acetate, but not by Olsen reagent, was significantly correlated with response.Herbage P in the first cut in 1978 was highly correlated with response to superphosphate; only sites with herbage P < 0·27% responded to P.