Rick, if your soil is sodic then gypsum may help its structure but otherwise not so much.
From Soil Amendments and Practices of Unproven Value:
"Gypsum, which is hydrated calcium sulfate (a low-solubility salt), is effective in treating sodic soils, which are soils high in exchangeable sodium. The sodium between soil particles attracts water, causing the soil to disperse. The dispersed particles seal the soil surface, reducing infiltration. Addition of gypsum replaces the sodium on the exchange sites with calcium, which results in flocculation of the soil particles into soil aggregates. The resultant sodium sulfate can then be leached out of the soil. Although gypsum does improve structure in sodic soils, it will not soften clay nor loosen compacted soil"
http://articles.extension.org/...
