Strippable coal in Iowa is overlain by sulfidebearing black shales capped with glacial till and loess. Weathering of these shales produces acid levels toxic to most plants, which necessitates rapid burial of the spoils. We have designed and tested a loess terrace method for returning Iowa strip mines to crop land as mining progresses. During the 1970s, corn growth and yields were monitored on various thicknesses of bess over leveled acid spoils in Mahaska County, Iowa. We evaluated the costs of reclaiming mined land to acceptable levels of productivity.
When saturated loess was emplaced, the resulting compaction seriously reduced corn yields during the initial years of reclamation. This problem was substantially reduced at an adjacent site by emplacement during a dry season. After compaction had been partially alleviated by growth of sweet-clover, chisle plowing, freeze-thaw, and increase in organic matter, yields were clearly proportional to loess thickness. During years of normal rainfall, yields of approximately 100 bushels per acre were produced from about 3 1/2 feet of loess cover. Four feet of loess cover produced yields equivalent to the county average in 1978 (114 bushels/acre) and 1979 (119 bushels/acre). Although the underlying spoils were toxic (pH 3–4), upward migration of acids into the loess was minor, even during drought years.
The cost of loess terrace reclamation was evaluated for 3 to 5 feet of loess cover. Assuming an average strippable coal seam thickness of 3 1/2 feet, the reclamation cost would have averaged 6.8% of the FOB price of coal during the 1970s. If the coal were trucked 50 miles to an electric utility, reclamation costs would have averaged 4.9% of the delivered price. Loess terrace reclamation would have increased the price of residential electricity by about 1%.