Spatial Distribution of Soil Carbon and Nitrogen Pools under Grazed Tall Fescue

Cattle (Bos taurus) behavior may be an important variable controlling the spatial distribution of soil C and N pools in long-term, grazed pastures. Shade and water sources are more frequented areas of a pasture that can also serve as camping areas where excreta are deposited. We sampled a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) under tall fescue (Festuca arundinacea Schreb.) at distances of 1, 10, 30, 50, and 80 m from permanent shade or water sources at the end of 8 and 15 yr of grazing. To a depth of 75 mm, soil bulk density was 1.15 Mg [m.sup.-3] at 1 m and averaged 1.00 Mg [m.sup.-3] at other distances from shade or water. To a depth of 300 mm, soil organic C was 4.6 kg [m.sup.-2] at 1 m, 4.3 kg [m.sup.-2] at 10 m, and [approximately equals] 4.0 kg [m.sup.-2] at distances of 30, 50, and 80 m from shade or water. Particulate organic C averaged 1.53 kg [m.sup.-2] at distances of 1, 10, and 30 m and 1.30 kg [m.sup.-2] at distances of 50 and 80 m from shade or water. Soil microbial biomass C, basal soil respiration, and net potential N mineralization were also greater nearer shade or water than farther away. Although lateral distribution effects were most dramatic at a depth of 0 to 25 mm, similar effects were observed even at a depth of 150 to 300 mm. Long-term cattle grazing in relatively small paddocks (0.7-0.8 ha) with permanent shade and water sources resulted in significant lateral and vertical changes in soil organic C and N pools.