Growth of Forbs, Shrubs, and Trees on Bentonite Mine Spoil under Greenhouse Conditions

Abstract

Revegetation on raw bentonite spoil with or without treatments is often more practical than replacing topsoil in areas where it is scarce or nonexistent. The effect of raw bentonite spoil treated with ponderosa pine sawdust on plant survival and growth was compared to other treatments including perlite, gypsum, straw, vermiculite, and no treatment. Plants tested were the droughtand salt-resistant species of fourwing saltbush (A triplex canescens (Pursh) Nutt.), rubber rabbitbrush (Chrysothamnus nauseousus (Pallo) Britt.), big sagebrush (Artemisia tridentata tridentata Nutt.), common winterfat (Ceratoides lanata (Pursh) Moq.), Rocky Mountain juniper (Juniperus scopulorum Sarg.), Russian olive (Elaegnusangustifolia L.), common yarrow (AchilleamUlifolium L.), and desert globemallow (Sphaeralcea ambigua Gray). Desert globemallow, fourwing saltbush, and rubber rabbitbrush had substantial growth and survival on sawdust, perlite, and vermiculite treated spoil. The growth promoting effect of sawdust is particularly promising; it is readily available and cost is minimal. Bentonite, a cream to greenish-gray colored clay consisting of the mineral montmorillonite (Gries 1974), occurs in much of the northern Great Plains as widespread beds interstratified with the dark gray marine shales. Bentonite mine spoil is commonly described as shales containing sodium montmorillonite. When wet, the bentonite spoil swells, and infiltration, permeability, and aeration approach zero. Excessive salt concentrations increase the osmotic potential of the spoil solution to a level that can be toxic to plants. Because of these problems, revegetation of bentonite mine spoil in arid and semiarid regions of the northern Great Plains, is extremely difficult (Bjugstad 1979). Several factors can be employed to improve revegetation efforts: (1) improving the physical and chemical conditions of the spoils, (2) covering bentonite spoils with topsoil and more favorable overburden, (3) using the most salt adaptable plants (Shannon 1979), (4) developing new genetic strains of salt adaptable plants for the future (Epstein et al. 1980), or (5) utilizing drip irrigation systems, but this may be expensive. Replacing the original topsoil to bentonite spoil has improved plant survival somewhat (Bjugstad 1979, Dollhopf et al. 1980, Dollhopf and Bauman 1981). However, much of the bentonite land has only shallow surface soil-less than 15 cm. In many places it is not practical to restore the original soil to bentonite-mined lands. This study was initiated to determine, based on greenhouse trials, the plant species most adaptive to spoil conditions and spoil amendments conducive to plant growth and establishment without topsoil.