TY - JOUR T1 - Statistical assessment of a paired-site approach for verification of carbon and nitrogen sequestration on Wisconsin conservation reserve program land JF - Journal of Soil and Water Conservation SP - 58 LP - 67 VL - 58 IS - 1 AU - C.J. Kucharik AU - J.A. Roth AU - R.T. Nabielski Y1 - 2003/01/01 UR - http://www.jswconline.org/content/58/1/58.abstract N2 - The threat of global climate change has provoked policy-makers to consider plausible strategies to slow the accumulation of greenhouse gases—especially carbon dioxide (CO2)—in the atmosphere. One such idea involves the sequestration of atmospheric carbon (C) in degraded agricultural soils as part of the Conservation Reserve Program (CRP). While the potential for significant C sequestration in CRP grassland ecosystems has been demonstrated, the paired-site sampling approach traditionally used to quantify soil C changes has not been evaluated with robust statistical analysis. In this study, 14 paired CRP (> 8 years old) and cropland sites in Dane County, Wisconsin, were used to assess whether a paired-site sampling design could detect statistically significant differences (ANOVA) in mean soil organic C and total nitrogen (N) storage. We compared 0 to 10 cm (0 to 3.9 in) bulk density and sampled soils (0 to 5 cm, 5 to 10 cm, and 10 to 25 cm [0 to 2 in, 2 to 3.9 in, and 3.9 to 9.8 in]) for textural differences and chemical analysis of organic matter (OM), soil organic C (SOC), total N, and pH. The CRP contributed to reducing soil bulk density by 13% (p < 0.0001) and increased SOC and OM storage (kg m−2 [lb ft−2]) by 13% to 17% in the 0 to 5 cm (2 in) layer (p = 0.1). We tested the statistical power associated with ANOVA for measured soil properties and calculated minimum detectable differences (MDD). We concluded that 40 to 65 paired sites and soil sampling in 5 cm (2 in) increments near the surface were needed to achieve an 80% confidence level (α = 0.05; β = 0.20) in soil C and N sequestration rates. Because soil C and total N storage was highly variable among these sites (CVs > 20%), only a 23% to 29% change in existing total organic C and N pools could be reliably detected. While C and N sequestration (247 kg C ha−1 yr−1 and 17 kg N ha−1 yr−1 [220 lb C ac−1 and 15 lb N ac−1]) may be occurring and confined to the surface 5 cm (2 in) as part of the Wisconsin CRP, our sampling design did not statistically support the desired 80% confidence level. We conclude that usage of statistical power analysis is essential to insure a high level of confidence in soil C and N sequestration rates that are quantified using paired plots. ER -