Management-intensive Grazing Affects Soil Health

Abstract. Management-intensive Grazing (MiG) on irrigated, perennial pastures has steadily increased in the western US due to pressure for reducing public lands grazing, overall declining land available for pasture, and decreasing commodity prices. However, there are still many unknowns regarding MiG and its environmental impact, especially with regards to soil health. Over a two-year period, we studied changes in soil health under a full-scale, 82 ha pivot-irrigated perennial pasture system grazed with ~ 230 animal units (AUs) using MiG. Soil analysis included 11 soil characteristics aggregated into the Soil Management Assessment Framework (SMAF), which outputs results for soil biological, physical, nutrient, chemical, and overall soil health indices (SHI). Positive impacts were observed in the biological SHI due to increases in microbial and enzymatic activities, even though soil organic C (SOC) remained relatively unchanged; however, positive biological SHI changes are likely precursors to future SOC increases. The nutrient SHI declined due to a reduction in plant-available soil P over time, potentially due to greater plant uptake. A negative impact was also observed in the physical SHI, driven primarily by increasing bulk density due to hoof pressure from cattle grazing. If managed correctly, results suggest that irrigated, MiG systems have the potential for success with regards to supporting grazing while promoting soil health for environmental and economic sustainability.