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Title: FATE OF GYPSUM SURFACE-APPLIED TO AN APPALACHIAN HILL PASTURE WATERSHED

Author
item Feldhake, Charles
item Ritchey, Kenneth
item Boyer, Douglas

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2001
Publication Date: 7/10/2001
Citation: Feldhake, C.M., Ritchey, K.D., Boyer, D.G. 2001. Fate of gypsum surface-applied to an Appalachian hill pasture watershed. Agricultural Water Management. 50:27-39.

Interpretive Summary: Many forage and crop species yield best with higher concentrations of calcium and lower concentrations of aluminum and hydrogen ions in soils than are found in many soils of Appalachia. While agricultural lime can remedy this problem near the soil surface, changing subsurface levels requires application of a more readily leached calcium salt such as gypsum. However, the resultant leaching of aluminum and hydrogen ions from subsoil as a consequence of applying gypsum, could potentially have negative impacts on local stream quality. We have found that applying gypsum, material that was a coal combustion by-product, to soils low in pH did not decrease the pH of watershed discharge or result in measurable aluminum in discharge flow. Calcium was retained in soils in greater amounts than would be predicted by rainfall leaching. However, Magnesium was leached from soils increasing levels in stream flow and decreasing the availability yof this essential nutrient for forages. The results suggest application o gypsum less than 5 tons per acre can increase subsoil calcium levels without compromising stream quality. Such applications may require careful management for other nutrients such a magnesium. This work is useful for scientists developing improved management systems for forage production on Appalachian hill land pastures. This work also is valuable for helping agricultural producers and energy industries utilize a calcium resource, that is a by product of scrubbing power plant exhaust in order to improve air quality, thus reducing disposal costs. This work will help improve the economic viability of small farms in Appalachia and help maintain lower costs for the power generation industry so consumers have affordable electricity.

Technical Abstract: Low pH soils leached with gypsum solutions have been shown to sorb gypsum thereby increasing calcium and improving root growth of some crops. However in some situations exchangeable aluminum is leached which could potentially cause adverse off-site impacts. In this study, 8250 kg ha-1 gypsum was applied to plots in a steep 4.3 ha pasture watershed in central Appalachia (predominantly Gilpin silt loam fine-loamy, mixed, mesic, Typic Hapludults) and measured changes in the 0-40 cm soil profile and changes in water chemistry at a flume below a seep which drains the watershed. After the end of the second growing season, and a total rainfall of 1.7 m, 46% of the applied gypsum calcium was still in the top 40 cm of soil. The rainfall had a 11.4% efficiency rate of transporting gypsum out of the top 40 cm compared to a saturated solution. Of the applied gypsum sulfate, 3.4% exited the watershed through stream flow. Maximum gypsum concentrations in stream flow, which were during a storm event, were 41 pp or less than 2% of saturation levels. While exchangeable aluminum decreased in the 20-40 cm soil layers in response to the gypsum application, no detectable aluminum was measured in stream flow at the flume. Sixty six percent of the exchangeable magnesium in the top 40 cm of soil in the treated plots was flushed from the soil profile. These findings indicate that as long as a minor part of a watershed has gypsum applied at rates less than 10,000 kg ha-1, off site environment impacts should be minimal. The major problem is maintaining adequate onsite magnesium levels for plant growth.