Effects of Gypsum Application Rate and Frequency on Corn Response to Nitrogen

The effects of gypsum as a soil amendment and its interaction with nitrogen (N) applications in corn (Zea Mays L.) production are largely unknown. A 4-yr field study was conducted in Ohio, USA to evaluate (i) the effects of gypsum rates and rate frequencies at varying fertilizer N rates on corn grain yields, ear-leaf and grain nutrient concentrations, and on soil nutrients, and (ii) the interactive effects between N and gypsum applications. A split-plot experimental design was used with N rates (0, 84, 168, and 252 kg N ha(-1)) as the main plot factor and either gypsum application rate (0, 1.1 and 2.2 Mg ha(-1)) or application rate frequencies (i.e., 1.1 Mg ha(-1) annually, 2.2 Mg ha(-1) bi-annually, and 4.4 Mg ha(-1) once every four years) as subplot factors. Overall, corn yield response to gypsum applications was inconsistent. A positive corn yield response to gypsum application occurred only in 2017 at the Northwest site. Gypsum applied at 4.4 Mg ha(-1) significantly decreased yields at the Northwest site in 2017 and at the Wooster site in 2016 suggesting that the best management strategy may be to apply lower gypsum rates either annually or biannually. Gypsum applications did not improve corn response to N at either study site but significantly increased tissue, grain and extractable soil S concentrations with concentrations decreasing as the application frequency decreased. This suggests that where S deficiencies may occur, an annual rate of 1.1 Mg ha(-1) or a bi-annual application of 2.2 Mg ha(-1) would increase S availability.