Stratification of Soil Properties By Depth in a Perennial Warm Season Pasture Overseeded with Cool Season Annuals.

Winter annuals are useful for providing forage for livestock, but their impacts on soil properties have not been examined in perennial pastures in humid subtropical southern United States. Chemical, physical, and biological soil properties were analyzed to examine soil health in perennial bahiagrass pasture in fall 2014 and 2015 and spring 2016. The site was privately owned and managed commercial grazing operation which had been overseeded in a mixture of winter annuals the past four fall grazing seasons. Prior to winter annual planting, samples (0-30cm) were collected across a topographic sequence (summit, backslope and footslope). Soil chemical assessments included macronutrients, pH, soil organic matter (SOM), soil organic C (SOC), and total nitrogen (TN) to 30cm. Microbial community structure (fatty acid profiles) and enzyme activity assays were conducted on samples collected to 15 cm. SOM, SOC, TN and microbial enzyme activity ratios by depth were used as a more accurate indicator of soil health (Franzleubbers, 2002). Stratification ratios for SOM, SOC, and TN were calculated using measurements from 0-7.5cm divided by measurements from 15-22.5cm. Enzyme activity ratios was determined by dividing measurements at 0-7.5cm by measurements at 7.5-15cm. The north facing footslope, northeast facing backslope, and Summit2 were found to have decreasing stratification of SOM over time (3.73 to 2.52, 3.13 to 1.57, and 3.22 to 1.99, respectively). Stratification of TN increased in the north facing footslope and Summit1 (25.82 from 3.69 and 7.38 from 2.31, respectively) in spring samples indicating potential seasonal effects. Summit2 had the highest stratification of SOC and β-glucosidase activity (4.84 and 8.74, respectively) regardless of sampling date. The decreasing SOM stratification with time may indicate that organic matter is moving deeper in the soil profile. The high stratification of SOC and β-glucosidase at Summit2 may be due to biomass of vegetative species at the soil surface.