PLANT-RESPONSES TO GYPSUM AMENDMENT OF SODIC BENTONITE MINE SPOIL

Abandoned bentonite mine spoils are extremely difficult to revegetate because of their high clay content, salinity, sodicity, low permeabili ty, and the semiarid climate of the area where bentonite mining occurs . Recent research has led to the development of technology utilizing s awmill wastes (chips, bark, and sawdust) to enable the successful reve getation of these lands. The use of wood residue amendments increased water infiltration, leaching of soluble salts, and vegetation establis hment; however, sodicity continued to be a problem and threatened to d estroy the established vegetation. Surface application of gypsum was e valuated to determine its effectiveness in ameliorating the spoil sodi city and its effect on plant growth. In a 3-year field study, surficia l gypsum amendment resulted in significant increases in perennial gras s biomass (150%) and canopy cover (140%). These changes were not evide nt until the second or third year after gypsum amendment. Annual forb biomass did not respond to gypsum amendment; however, canopy cover did exhibit a significant increase in the second year at lower wood resid ue amendment rates. This research demonstrates that surface applied gy psum can be effective in ameliorating bentonite spoil sodicity when ap plied to established plant communities.