Transformations of Nitrogen‐15‐Labeled Fertilizer Nitrogen and Carbon Mineralization in Incubated Coal Mine Spoils and Disturbed Soil

Abstract

AbstractLimited information is available concerning N transformations in exposed geologic materials of disturbed lands in the western USA. A laboratory incubation study was therefore conducted using 15N to trace the dynamics of fertilizer 15NH+4 added to samples of one topsoil and five coal mine spoils from Colorado and Wyoming. Carbon dioxide evolution, N mineralization, nitrification, microbial immobilization, and NH+4 fixation within clay minerals were monitored over time. The organic matter in three of the spoils was considerably less susceptible to microbial decomposition than the topsoil organic matter, whereas the organic matter in the fourth spoil was slightly less susceptible than, and in the fifth spoil comparable to, topsoil organic matter in susceptibility to microbial decomposition. However, the amount of plant‐available N mineralized was at least five times higher in the topsoil than in any of the spoil materials. The data suggest that, under field conditions, none of the spoil materials evaluated in this study will likely be able to adequately supply the N requirements of a reseeded plant community. The significantly more active microbial population of the topsoil immobilized more of the added 15NH+4 than in any of the spoils except the shale, whereas more of the added 15NH+4 was nitrified and remained as NO−3 in the spoils than in the topsoil. The data indicate that under field conditions, a larger proportion of added fertilizer NH+4 will be susceptible to loss via NO−3 leaching or volatilization in the spoils than in the topsoil.