Assessment of Subsoil Sulfate and Manure as Sources of Plant Available Sulfur

The amounts of sulfate-sulfur in profiles of eight Wisconsin soils and the contribution of plant available sulfur from manure applications at three locations was determined. Total profile contents of SO4-S ranged from 19.2 to 186.3 kg/ha in a Plainfield lfs at Hancock and a Plano sil at Sun Prairie, respectively. Most of the soils had substantial amounts of SO4-S in the subsoil relative to the surface making S deficiency unlikely. Cumulative amounts of SO4-S to a depth of 90 cm was highly correlated to soil organic matter in the surface 30 cm (r=.782**). At each depth increment, SO4-S was negatively related to soil pH. The distribution of SO4-S within profiles are discussed relative to soil properties. Manure treatment effects were difficult to detect because of inherently high SO4-S levels in the experimental soils. The addition of high rates of nitrogen, through manure or fertilizer treatments resulted in occasional significant reductions in subsoil SO4-S at Sun Prairie and Baraboo. In 1982 at Sun Prairie, the addition of 88 and 121 Mg/ha dairy manure and 274-37-158 kg/ha N-P-K resulted in a significant decrease in total profile amounts of SO4-S. Manure applications did not significantly affect levels of SO4-S in total profiles at Fall River and Baraboo. A contribution of S from dairy manure was not obtained for the experimental period