Surface Soil Changes during Twelve Years of Pasture Management in the Southern Piedmont USA

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Abstract
Surface soil characteristics are of key importance in assessing the sustainability of agricultural management systems. We evaluated the factorial combination of nutrient source (inorganic, mixed organic + inorganic, and organic as broiler litter) and forage utilization (unharvested, low and high cattle grazing pressure, and hayed) on soil organic matter during 12 yr of pasture management on a Typic Kanhapludult in Georgia. Nutrient source had very little effect on bulk density, soil organic C (SOC), and total soil N (TSN). Forage utilization greatly affected all soil properties, more so nearest the surface. For example, SOC at a depth of 0 to 3 cm under low grazing pressure was 47.6 g kg−1 and under haying was 28.8 g kg−1 (P < 0.001), while at 3 to 6 cm it was 20.1 and 14.9 g kg−1, respectively (P = 0.04), and at 6 to 12 cm it was 12.7 and 11.0 g kg−1, respectively (P = 0.59). Soil bulk density was inversely related to SOC. Total SOC (0–20 cm) plus surface residue C was 3.6 ± 3.6 Mg C ha−1 greater (mean ± standard deviation among six nutrient source × forage utilization comparisons) in the zone nearest shade and water sources than farther away. Sequestration of TSN in the surface 6 cm averaged 8 ± 8 kg N ha−1 yr−1 (mean ± standard deviation among three nutrient source comparisons) when hayed, 31 ± 15 kg N ha−1 yr−1 when left unharvested, and 74 ± 5 kg N ha−1 yr−1 when grazed by cattle with either low or high grazing pressure. These results indicate the large potential of well‐managed grazing systems to improve the quality and functioning of soils in the southeastern United States.