Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2008
Publication Date: 7/31/2008
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2008. Soil physical responses to cattle grazing cover crops under conventional and no tillage in the Southern Piedmont USA. International Journal of Soil and Tillage Research. 100:141-153. Interpretive Summary: Integration of crops and livestock could provide economic benefits to producers by intensifying land use and improving resource efficiency, but how this management might affect soil compaction, water infiltration, and soil strength has not been well documented. Scientists at the USDA-Agricultural Research Service in Watkinsville Georgia conducted a 3-year field experiment, whereby annual crops were grown following termination of perennial pasture. Two tillage systems were tested: (1) moldboard plow initially to break sod and disking thereafter and (2) no tillage with herbicide application only. Two cropping systems were tested: (1) sorghum and corn in summer with rye as winter cover crop and (2) winter wheat with pearl millet as summer cover crop. Two cover crop management strategies were tested: (1) cover crops grazed by cattle and (2) cover crops left unharvested to mulch the soil. Conventional tillage loosened soil initially compared with no tillage, but the effect diminished with time. Grazing of cover crops had no effect on soil bulk density, perhaps because of the high soil organic matter content following perennial pasture that mitigated compaction. Soil aggregation was degraded by conventional tillage. Stability of soil aggregates was unaffected by grazing of cover crops in both tillage systems. Water infiltration was reduced with grazing of cover crops when soil water content was high. Soil strength was greater under no tillage than under conventional tillage. It was also greater under grazed than under ungrazed cover crops with conventional tillage, but not different between cover crop system with no tillage. Overall, the introduction of cattle to consume the high-quality cover crop forages did not cause substantial physical damage to the soil. Crop and cattle producers who adopt integrated crop-livestock systems are encouraged to utilize conservation tillage management techniques to help preserve surface soil organic matter and prevent deterioration of soil quality. This recommendation can be applicable to small- and medium-sized farms throughout the southeastern USA.
Technical Abstract: Grazing of cover crops in grain cropping systems can increase economic return and diversify agricultural production systems, but the environmental consequences of this intensified management have not been well documented, especially under different tillage systems. We conducted a multiple-year investigation of how cover crop management (grazed and ungrazed) and tillage system [conventional (CT) and no tillage (NT)] affected soil physical properties (bulk density, aggregation, infiltration, and penetration resistance) on a Typic Kanhapludult in Georgia. Responses were determined in two cropping systems: summer grain / winter cover crop and winter grain / summer cover crop. Soil bulk density was reduced (P = 0.02) with CT compared with NT to a depth of 30 cm at the end of ½ yr, but only to a depth of 12 cm at the end of 2 and 2 ½ yr. Grazing of cover crops had no effect on soil bulk density. Water-stable macroaggregation was reduced (P < 0.01) with CT compared with NT to a depth of 12 cm at all sampling times during the first 2 ½ yr of evaluation. Stability of macroaggregates in water was unaffected by grazing of cover crops in both tillage systems. Across 7 sampling events during the first 4 yr, there was a tendency (P = 0.07) for water infiltration rate to be lower with grazing of cover crops (5.6 mm min-1) than when ungrazed (6.9 mm min-1), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0 to 10 cm (P = 0.001) and the difference was greater in ungrazed than in grazed systems (P = 0.06). Biannual CT operations may have alleviated any surface degradation with animal traffic, but the initially high level of soil organic matter following long-term pasture and conversion to cropland with NT may have buffered the soil from any detrimental effects of animal traffic. Overall, the introduction of cattle to consume the high-quality cover crop forage did not cause substantial damage to the soil.