Comparison of carbon rich soil amendments for reclamation of southwest Wyoming natural gas well-pads

Wyoming is one of the highest natural gas producers in the United States. The associated natural gas well-pad construction and reclamation practices, resulting from energy product extraction, cause drastic changes to soils and native vegetation communities. Successful reclamation of disturbed sites is challenging, as Wyoming soils are often alkaline, with low organic matter levels, and growing conditions are cold and dry. Carbon (C) additions, meant to counter invasive plant establishment and improve soil conditions, have been utilized in several rangeland studies in attempts to expedite and improve reclamation efforts, but the effectiveness of these amendments is poorly understood. The purpose of this study was to compare C-rich soil amendments, across nine treatments and a control, for use as a reclamation practice on southwest Wyoming natural gas well-pads. More specifically, we evaluated the cost of applying the treatments; their ability to improve soil conditions; reduce invasive plant species; and increase native plant species. Three rates of straw, woodchips (WC), and a woodchip/compost (WC+C) mixture were incorporated into soils on two reclaimed well-pad sites in southwest Wyoming. One site was on the Jonah Field, an area of dense well-pad development and accompanying high invasive plant populations. These conditions contrasted the second site located on the Pinedale Anticline, found at higher elevations and in a less dense distribution of well-pad development and invasive plants, compared to the Jonah Field site.;Over the course of 12 months, following application of the soil amendments, C additions generally had positive effects on soil conditions by significantly decreasing pH and increasing labile and physically free organic C levels at both study sites, and decreasing calcium carbonate levels on the Pinedale Anticline. These soil characteristics were most improved by the high rates of straw and WC, however, the seeded native plant species under the high straw, performed less well, as did vegetation cover under the high WC treatments, on the Pinedale Anticline. Among all treatments, however, the high application rate of WC had the most positive significant effects by treatments, compared to control plots, on the Jonah Field and Pinedale Anticline sties.;Treatments successfully decreased soil mineral nitrogen (N), with significantly lower levels measured in almost all treatments, compared to the control. Soil labile and physically free organic N levels were also generally lowered by treatments. Decreased mineral N did not cause a significant change to invasive plant species establishment, however, the lowest mineral N levels were measured under the high straw and WC treatments at both sites. These same treatments had the lowest invasive plant species densities on the Pinedale Anticline, but were not significantly different compared to the control. The high WC+C treatment on the Jonah Field had the lowest invasive plant densities and corresponding highest native seeded plant densities, but these densities were also not significantly different than those measured in the control plots. The low straw treatment significantly increased shrub and forb densities on the Jonah Field, and shrub densities on the Pinedale Anticline. The medium straw treatment also significantly increased forb densities on the Jonah Field.;Comparison of total estimated costs of treatment use, including costs of delivered materials, application, and incorporation, found WC treatments to be about 23% more expensive than the WC+C treatments and about 15% more expensive than the straw treatments. Considering the study's comprehensive findings, C additions seem most useful on sites with an invasive plant species problem, such as found on the Jonah Field, or where alkaline soil conditions are a primary factor hindering reclamation success. Additional time will allow better assessment of the sustained effects of the amendments' contribution to reclamation success.