Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/15/2011
Publication Date: 5/30/2012
Citation: Franzluebbers, A.J., Stuedemann, J.A., Franklin, D.H. 2012. Water infiltration and surface soil structural properties as influenced by animal traffic in the Southern Piedmont USA. Renewable Agriculture and Food Systems. 28:160-172. Interpretive Summary: Surface-soil characteristics are of particular importance in determining the environmental quality of a location, but also for determining the environmental quality of neighboring ecosystems, if considerable erosion, runoff, and gaseous emissions were to occur. Scientists at the USDA-Agricultural Research Service in Watkinsville Georgia evaluated water infiltration and penetration resistance (measures of surface soil compaction) and rainfall/runoff relationships during a 12-year pasture experiment that was differentiated by (1) source of nutrients (inorganic versus organic) and (2) how forage was utilized (unharvested, hayed, or grazed by cattle). Soil was denser immediately below the soil surface under grazed pastures, which caused higher penetration resistance and lower water infiltration than unharvested grass. However, greater accumulation of surface residue and soil organic carbon under grazed pastures compared with hayed management led to similar water infiltration, despite firmer soil when grazed. Runoff predominately occurred with a small percentage (15%) of rainfall events that exceeded the soils’ capacity to allow entry of water. These data suggest that well-managed pastures have high capacity to cycle water through soil, despite evidence of some soil compaction. This is because accumulation of surface residue and soil organic carbon are able to mitigate much of the negative effects of animal trampling on soil hydrologic conditions by creating a biologically active surface soil. Cattle grazing of mixed bermudagrass / tall fescue pastures can be considered a viable strategy to rehabilitate millions of acres of degraded cropland in the southeastern USA.
Technical Abstract: Surface-soil structural condition in long-term perennial pastures is expected to be modified by how forage is (a) harvested through haying or grazing and (b) stimulated through source of nutrient application. We determined the effects of harvest management and nutrient source on macropore filling, rate of water infiltration, and penetration resistance in a bermudagrass [Cynodon dactylon (L.) Pers.] / tall fescue (Lolium arundinaceum Schreb. S.J. Darbyshire) pasture on a Typic Kanhapludult (Acrisol) in Georgia. Associated changes in bulk density, soil organic C, surface residue C, and ground cover were also determined. During a period when soil was wet (61% water-filled pore space), rate of water infiltration was 2.3 + 0.2 times greater when forage was left unharvested as when hayed or grazed. During a period when soil was dry (28% water-filled pore space), rate of water infiltration was not statistically different among harvest management practices, but macropore filling was 62% greater when forage was left unharvested as when hayed. Penetration resistance of the surface 10 cm was significantly affected by harvest management, following the order: unharvested (64 J) < hayed (101 J) < low grazing pressure (122 J) < high grazing pressure (139 J). Water infiltration during the wet period was negatively related (p < 0.01) to soil water content (r = -0.57), penetration resistance at 0-10 cm depth (r = -0.50), and bulk density at 3-6 cm depth (r = -0.53), but was positively related to surface residue C (r = 0.47) and soil organic C concentration at 12-20 cm depth (r = 0.42). Although cattle grazing increased soil penetration resistance, overall surface-soil structural condition limited water infiltration only when soil was wet. High surface residue C and soil organic C under grazed systems helped to alleviate the increase in firmness caused by cattle traffic. These results suggest that complex soil physical and biological interactions occur in pastures, and that well-managed grazing systems with excellent ground cover could have adequate hydrologic condition to promote pasture productivity and avoid environmental contamination. Further research is warranted to quantify the linkages between surface soil quality and environmental quality.