Soil physical responses to cattle grazing cover crops under conventional and no tillage in the Southern Piedmont USA

摘要

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; initial moldboard plowing and thereafter disk tillage) 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 30cm at the end of 0.5 year, but only to a depth of 12cm at the end of 2, 2.5, and 4.5 years. Grazing of cover crops had little effect on soil bulk density, except eventually with 4.5 years of management. Water-stable macroaggregation was reduced (P <=0.01) with CT compared with NT to a depth of 12cm at all sampling times during the first 2.5 years 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 years, there was a tendency (P =0.07) for water infiltration rate to be lower with grazing of cover crops (5.6mmminp#) than when ungrazed (6.9mmminp#), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0-10cm (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.