CASE STUDY: EFFECTIVENESS OF COMMERCIAL COMPOST SOIL AMENDMENT IN MONTANA UPLAND AND RIPARIAN REVEGETATION 1

When using borrow dirt as cover-soil, revegetation often stagnates or declines in one decade or less, especially in cold, semiarid climates, due to infertility and lack of nutrient cycling. Fresh cover-soil is dirt; soil is distinguished by the organisms living in and on it. Compost amendment is intended to speed the conversion of dirt to soil by initiating an incipient soil food web. Compost provides microorganisms capable of degrading a wide variety of organic substances and the carbon and nutrients to sustain them until vascular plants provide fresh substrates and eventually a diverse array of food sources from root exudates to microbial cells. Or so it was thought when the two reclamation projects discussed in this paper began, one a Superfund remediation on Silver Bow Creek and the other waste dump reclamation at the Golden Sunlight Mine. The two projects are on opposite sides of the Continental Divide in southwest Montana. Applying and incorporating compost along Silver Bow Creek was easy; steep slopes at the gold mine limited both application and incorporation. One decade after seeding, microbiological analyses of composted and uncomposted soils failed to demonstrate greater diversity in composted cover- soils at the riparian Superfund site. Neither were short-term microbiological effects of compost amendment detectable at the hard-rock mine. Vascular plant cover likewise did not show a significant difference between composted and uncomposted treatments at the riparian site. This raises the question of whether introduced soil microbes drive revegetation or vice-versa, the vascular plants lead and soil microbiology follows. The microbiological activity that matters may be restricted mainly to the rhizosphere, at most a few percent of the bulk soil. Thermophilic microorganisms in moist compost simply may not survive in soils that dry and freeze. Soil biology may be one aspect of the recovery process that cannot be expedited using biologically active organic amendment. Compost specifications also are discussed.