Ranch-scale soil health, forage quality, and cattle grazing capacity linkages in a high-elevation steppe

The sustainability of rangeland grazing enterprises hinges on healthy and functioning soil resources. Yet information about how rangeland soil features influence livestock production has lagged relative to agronomic crop production. We established a ranch-scale assessment in Wyoming, USA to better understand soil health and livestock production. We integrated 26 years of animal day per hectare grazing records to relate livestock production to pasture-scale soil characteristics. In 2017, we measured 23 soil variables, and 11 forage variables (for Pascopyrum smithii) of 11 grazed pastures from 68 to 146 ha and three ungrazed exclosures. Pastures were stratified across animal day pasture categories ("Low," "Medium," "High," and "None" or exclosure; considered a carrying capacity index). Significant relationships were found between nine of the 23 soil response variables but only one of the 11 forage response variables relative to the animal day pasture categories. Statistical analysis indicated significantly higher % soil organic carbon and forage lignin in the High animal day pasture category relative to the Low Animal Day pasture category (both p-values <0.05). No significant relationship was found between the Animal Day pasture category and forage crude protein (p = 0.3). The principal component analysis explained 98.22% (cumulative for the first two axes) of the variation of the soil health variables but was less insightful for forage quality variables (71.1% of variation explained). Soil organic carbon is a suitable indicator of animal days in pasture and may serve as a useful rangeland soil health indicator for livestock producers.