|STUEDEMANN, JOHN - Retired ARS Employee|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2016
Publication Date: 11/6/2015
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2015. Does grazing of cover crops impact biologically active soil C and N fractions under inversion and no tillage management? Journal of Soil and Water Conservation. 70:365-373.
Interpretive Summary: Cover crops are a key component of conservation agricultural systems. Reluctance by producers to adopt this practice may be partially due to the cost of establishment without immediate return in yield. The practice is beneficial to yield and enhancement of soil quality in most regions only in the long-term. A scientist at the Plant Science Research Unit in Raleigh, North Carolina teamed with a former scientist in USDA-Agricultural Research Service from Watkinsville, Georgia to evaluate the effects of grazing cover crops on biologically active soil organic matter fractions during seven years of continuous management. Grazing of cover crops by cow/calf pairs resulted in only minor changes in organic matter fractions – the most notable were for an increase in soil microbial biomass in surface soil under no tillage. Very few negative effects of grazing occurred on these active soil organic matter fractions. Grazing of cover crops in the southeastern USA can be recommended, and due to the economic benefit from cattle gain rather than simple cost of planting a cover crop, it is conceivable that the strategy of cover crop grazing could help promote greater adoption of cover crop utilization on more farms throughout the region. Results from this study will be important for producers to understand the value of cover crops, as well as for conservation organizations and government agencies wanting to promote conservation practices to promote soil health improvement.
Technical Abstract: Cover crops are a key component of conservation cropping systems. They can also be a key component of integrated crop-livestock systems by offering high-quality forage during short periods between cash crops. The impact of cattle grazing on biologically active soil C and N fractions has not received much attention. We investigated the impacts of tillage (conventional disk and no tillage) and cover crop management (ungrazed and grazed) on biologically active soil C and N fractions from biennial sampling during 7 years of continuous management. Soil microbial biomass C was unaffected by cover crop management under conventional tillage, but was enhanced with grazing compared with no grazing under no tillage at a depth of 0-6 cm, as well as at 0-30 cm. The same effect occurred for the flush of CO2 following rewetting of dried soil during 3 days of incubation at a depth of 0-6 cm only, while it occurred for cumulative C mineralization during 24 days of incubation at a depth of 0-30 cm only. Grazing effects on net N mineralization during 24 days of incubation and residual soil inorganic N were non-existent. All biologically active fractions of soil C and N were highly stratified with depth under no tillage and less so under conventional tillage. Cumulative stocks of soil C and N fractions to a depth of 0-30 cm were generally not significantly different between cover crop management systems, nor between tillage systems, except for (a) lower soil microbial biomass C with than without grazing under conventional tillage, (b) greater soil microbial biomass C with than without grazing under no tillage, and (c) lower cumulative C mineralization during 24 days under no tillage than under conventional tillage. Grazing of cover crops in the southeastern USA can be recommended, and due to the economic benefit from cattle gain rather than simple cost of planting a cover crop, it is conceivable that the strategy of cover crop grazing could help promote greater adoption of cover crop utilization on more farms throughout the region.