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.