Soil organic carbon variability and sampling optimization in Montana dryland wheat fields

ABSTRACT: Soil organic carbon varies spatially as a function of short-range and landscape scale variability and is influenced by natural soil variability, soil management, and the variability associated with soil sampling techniques. Accurate measurement methods and efficient sampling designs are needed to determine the net carbon change over time as a function of soil management changes. Soil organic carbon sampling variability in paired no-till and tilled dryland wheat fields in Montana was examined. Paired fields at two locations were chosen with soils, cropping system, landscape position, and climatic conditions similar within each pair. Sampling variability in soil organic carbon for the 0 to 10cm depth was quantified among cores, microsites, and fields. Soil samples were analyzed for total and inorganic C, and particle-size distribution. Stratifying by soil-landscape association likely reduced soil organic carbon sample variability. Including percent clay as a covariant reduced soil organic carbon variance 40-fold (site level), however variance within sites (tillage effect) remained unchanged. Soil organic carbon was greater in no-till fields than tilled fields (P