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Nitrogen Mineralization and Nitrification in a Cretaceous Shale and Coal Mine Spoils¹

ABSTRACT

Knowledge of rates and amounts of N mineralization in geologic strata is needed to predict N availability to plants when these materials are disturbed by mining or construction and left as surface or subsurface plant-growth media. Laboratory incubations were conducted to determine ammonification and nitrification rates in a Cretaceous shale, two strip-mine coal spoils, and a soil from a strip mine in northwestern Colorado. The total N concentration in the soil (1193 ppm), a vegetated spoil (1,083 ppm), and the shale (1112 ppm) were similar, while that of the fresh spoil was lower (730 ppm). No net N mineralization was measured in the shale, and less than 6 ppm NO₃^--N accumulated in the fresh spoil during a 168-day incubation. However, net mineralization of 49-ppm NO₃^--N was found in the vegetated spoil and 75-ppm NO₃^--N in the soil during the same incubation period.

Nitrification of added NH₄⁺ (60 ppm NH₄⁺-N) was measured in the shale, spoils, and soil. Accumulated levels of NO₃^--N were 100 ppm in the vegetated spoil and 117 ppm in the soil after a 168-day incubation. However, only 36-ppm NO₃^--N accumulated in the fresh spoil and no NO₃^--N accumulated in the shale during the same incubation period.

Rates and total amounts of CO₂ evolution from the geologic materials resembled that from the soil, indicating considerable heterotropic microbial activity in these geologic materials. The addition of NH₄⁺ did not significantly affect the rate or amount of CO₂ evolution from the geologic or soil materials, indicating that heterotropic microorganisms were capable of using the forms of N present in the geologic materials.

¹ Published by the Colorado State Univ. Exp. Stn. as Scientific Series Pap. no. 2207 and supported in part by the Climax Molybdenum Co. This research was conducted as partial fulfillment of the requirements for the M.S. by the senior author and presented by her before Div. A-5, Am. Soc. of Agron. Meetings at Knoxville, Tenn., 13 Aug., 1975.

² Formerly Research Graduate Assistant, Colorado State Univ., Fort Collins (now Soil Scientist, USDA-ARS, Fort Collins), and Associate Professor, Dep. of Agronomy, CSU, Fort Collins, CO, respectively.

Received for publication January 31, 1977. Accepted for publication May 5, 1977.