CALCIUM-SULFATE OR COAL COMBUSTION BY-PRODUCT SPREAD ON THE SOIL SURFACE TO REDUCE EVAPORATION, MITIGATE SUBSOIL ACIDITY AND IMPROVE PLANT-GROWTH

Removal of sulfur dioxide from hue gas produced by coal-burning power plants has increased the availability of by-products that may be usefu l as soil amendments for agriculture. We studied the effects of surfac e layers (caps) of fluidized bed combustion residue-fly ash mixture (F BCR-FA) or calcium sulfate on reduction of evaporative water losses an d improvements in subsurface acid soil chemical characteristics. Caps 3.8 cm thick of porous FBCR-FA, hydrated commercial calcium sulfate (C CS), or soil (check) were placed on columns of coarse-loamy, mixed, me sic Umbric Dystrochrept soil of pH 4.2. After the addition of 40 cm of water during a 16-week period, mean daily water loss from the column with the FBCR-FA cap was 0.51 mm compared to 0.98 mm in the check. Mea n increase in soil exchangeable Ca in the 5- to 40-cm depth for the CC S treatment was 0.83 cmol(c) kg(-1) and mean pH (H2O) increase was 0.2 1 units. Mean KCl-extractable Al decreased from 6.08 to 5.52 cmol(c) k g(-1). Roots of sudangrass (Sorghum bicolor (L.) Moench) planted in th e columns after removal of the caps reached 2 cm depth in the control, 18 cm in the FBCR-FA and 38 cm in the CCS treated columns after 47 da ys of growth. The gypsum cap was effective in improving deep rooting i n acid soils and the FBCR-FA cap reduced evaporative water losses.