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Carbon amendments have been proposed as a way to reduce the invasion of non-native species. I studied the cumulative effects of three years of carbon amendments on previously disturbed mixed-grass prairie sites near Boulder, Colorado. Analysis of soil inorganic nitrogen during the third field season indicated a statistically significant but short-term nitrogen reduction in response to addition of a combination of sugar and sawdust treatments.
The carbon amendments significantly reduced plant foliage production from an average of 377 g/m2/yr on control plots to an average of 219 g/m2/yr on treated plots. Undesirable species such as diffuse knapweed (Centaurea diffusa) exhibited this biomass response, and seed production also decreased slightly. However, after three years of treatment there was no increase in desirable, reseeded species such as Western wheatgrass (Agropyron smithii). I suggest that the carbon amendment treatment alone is an inadequate remediation technique in areas exposed to extensive seed rain by exotic species.
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