Long-term pasture management impacts on eolian sand soils in the southern mixed-grass prairie

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Mixed grass pastures which occupy the eolian sand dunes of the southern Great Plains provide stabilizing soil cover, soil carbon (C) storage, and are a critical resource for livestock production. Large areas of dunes cover the American Great Plains, were active 700–1000 years ago during periods of frequent drought and have the potential to reactivate under forecasted climate scenarios and poor management. This study determined the soil age and development of eolian sandy soils and evaluated long-term grazing of native and improved pasture on root carbon, soil organic C (SOC), stable isotopes of soil fractions, and other soil properties. Pasture treatments included grazed and ungrazed (50 + yrs), improved pastures (28–50 yrs), and winter wheat (Triticum aestivum) or go-back grass (for 28–30yrs). Improved pasture grass species included both native (switchgrass (Panicum virgatum L.), and sand bluestem (Andropogon hallii Hack.) and non-native (weeping lovegrass (Eragrostis curvula (Schrad.) Nees)), and caucasian bluestem (Bothriochloa bladhii (Retz.) S.T. Blake) species. The Eda soil age was very recent and ranged from present at the surface to <1200 to <1600 yr BP (by luminescent or 14C dating, respectively) at the bottom of the soil profile (~130 cm). Long-term moderate grazing had relatively little impact on soil properties compared to ungrazed pastures. Soil C was dependent on grass root biomass across all improved pasture treatments, but with few differences among individual grasses or long-term pastures. Most improved pasture treatments either increased or maintained indicators of soil health (SOC, soil organic nitrogen (SON), mineral-associated carbon (Cmin-C), particulate organic matter carbon (POM-C), and silt and clay content). However, soils under winter wheat and sand bluestem had a third the SOC and SON of pasture, indicating soil degradation. Long-term grazing is a resilient practice that can stabilize these sandy soils and increase soil health. Soil protection is necessary should global warming result in drought and/or high winds and increase the potential for reactivation of eolian sand movement.