Response of Irrigated Corn to Sulfur Fertilization in the Atlantic Coastal Plain

Accurate prediction of yield response by corn (Zea Mays L.) to S fertilization on the coarse-textured soils of the Atlantic Coastal Plain requires information on availability and persistence of subsoil SO₄-S, potentially mineralizable soil S, and S added in irrigation and precipitation. A 3-yr study was conducted with irrigated corn on four soils possessing characteristics commonly associated with S deficiency. A factorial combination of S application rate (0, 33, 67, 101 kg ha⁻¹) and method (single broadcast at planting, split) was used. Grain yield, and S concentrations and N/S ratios of early whole plants (EWP) and ear leaves (EL) were determined. Extractable SO₄-S (0–100 cm) levels and inputs of S from irrigation and precipitation were measured in each year; mineralizable S in Ap horizons of all soils was determined by two incubation methods (leached and nonleached). Although application of S generally increased plant S concentrations, significant yield increases occurred in only three of the 12 site-year combinations. Critical values for S and N/S, based on combined data from responsive sites, were 2.1 and 1.6 g S kg⁻¹ and 18.7 and 20.3, for EWP and EL, respectively. Lack of yield response was attributed to subsoil SO₄-S, (average, 0–100 cm = 170 kg S ha⁻¹, mineralizable S (average = 80 kg ha⁻¹, leached method) and S contained in irrigation or precipitation (annual average = 7.5 kg ha⁻¹). Yield increases obtained at the most responsive site may have been caused by increased immobilization of S, due to no-tillage management, the presence of a physical barrier to root penetration at 40 to 60 cm, or subsoil Al. Successful prediction of corn response to S fertilization in Coastal Plain soils will require a comprehensive program that combines subsoil sampling and selective plant analysis, concentrated on sites identified as potentially responsive based on soil properties. Published as Misc. Paper no. 1056 by the Delaware Agric. Exp. Stn.