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Soil and Rhizosphere Microorganisms in Amended Coal Mine Spoils¹

ABSTRACT

Topsoil is usually respread over strip-mined land during reclamation. In some instances, spoil could be used as a medium for revegetation. The objectives of this study were to compare microbial parameters in spoil and soil and determine the effect of spoil amendment on these microbial parameters.

Representative samples from a topsoil stockpile, a nonvegetated spoil, a reclaimed area, and an adjacent undisturbed surface soil were collected from the San Juan coal mine near Farmington, N. Mex. Additional samples of spoil and stockpiled topsoil were used in a greenhouse pot experiment to determine the influence of spoil amendment on microbial parameters. The treatments included spoil, spoil plus topsoil inoculant, spoil plus alfalfa hay and fertilizer (both with and without topsoil inoculant), and spoil plus gamma-irradiated sewage sludge (both with and without topsoil inoculant). The pots were planted to Bouteloua gracilis and microbial determinations of the spoil made after 5 months. Later the same pots were replanted to Atriplex canescens and microbial determinations made of the rhizosphere 7 months after planting. Microbial parameters measured included numbers of aerobic heterotrophic bacteria, Streptomyces, fungi, ammonium oxidizers, and aerobic asymbiotic nitrogen fixers, dehydrogenase activity, and fungal genera distribution.

The undisturbed soil and reclaimed area had comparable microbial numbers, dehydrogenase activity, and fungal genera distribution. Microbial numbers and dehydrogenase activity of stockpiled topsoil and nonvegetated spoil were low and the fungal genera distribution was narrow.

Topsoil inoculation did not increase microbial parameters of the spoil or of the rhizosphere of A. canescens. Spoils appeared to be unable to support an active and varied indigenous flora or the microorganisms introduced by the topsoil inoculant. Organic amendment of either sludge or alfalfa increased all microbial parameters. The increased numbers, dehydrogenase activity, and distribution of fungi were particularly evident in the rhizosphere. Providing an available carbon source was more critical in stimulating an active and varied spoil microflora than was supplying an inoculant source.

¹ Contribution from the Dep. of Agronomy, New Mexico State Univ., Las Cruces, NM 88003. Journal Art. no. 891, Agric. Exp. Stn., New Mexico State Univ. This work was supported by a grant from the Rocky Mountain Forest and Range Exp. Stn., Forest Service, USDA, Cooperative Agreement no. 16-850-CA.

² Former Graduate Research Assistant and Assistant Professor of Soil Microbiology, respectively. The Senior Author's current address is Rocky Mountain Forest and Range Exp. Stn., 2205 Columbia SE, Albuquerque, NM 87106.

Received for publication September 9, 1981. Accepted for publication April 5, 1982.