Interpretive Summary: Interest in gypsum use as a soil amendment to improve agriculture production is increasing. This interest is attributed to the recent availability of flue gas desulfurization (FGD) gypsum in major agricultural producing regions. FGD gypsum is a synthetic gypsum source produced as a by-product of removing sulfur from the burning coal fumes at utility plants. Currently, there is limited data on the benefits, positive and negative, of using FGD gypsum on agricultural soils. This manuscript reviews FGD gypsum use in agriculture and describes its potential benefits, introduces the special collection of papers on the benefits to agriculture, discusses knowledge gaps, and provides direction for future research needs. The research discussed in this special collection of papers as well as previous work reviewed suggests that FGD gypsum could provide potential benefits to agriculture.

Technical Abstract:
Interest in using gypsum as a management tool to improve crop yields and soil/water quality has recently increased. Abundant supply and availability of flue gas desulfurization (FGD) gypsum, a by-product of scrubbing sulfur (S) from combustion gases at coal-fired power plants, in major agricultural producing regions within the last two decades has attributed to this interest. Currently, published data on the long-term sustainability of FGD gypsum use in agricultural systems is limited. This has led to organization of the ASA Community “By-product Gypsum Uses in Agriculture” and a special collection of nine technical research articles on various issues related to FGD gypsum uses in agricultural systems. A brief review of FGD gypsum, rationale for the special collection, overviews of articles, knowledge gaps, and future research directions are presented in this introductory paper. The nine articles are focused in three general areas: (1) mercury (Hg) and other trace element impacts, (2) water quality impacts, and (3) agronomic responses and soil physical changes. While this is not an exhaustive review of the topic, results indicate that FGD gypsum use in sustainable agricultural production systems is promising. The environmental impacts of FGD gypsum are mostly positive with only few negative results observed, even when applied at rates representing cumulative 80-year applications. Thus FGD gypsum, if properly managed, seems to represent an important potential input into agricultural systems.