Grazing winter rye cover crop in a cotton no-till system: Soil strength and runoff

Authors: Schomberg, Harry; ENDALE, DINKU; Balkcom, Kipling; RAPER, RANDY - OKLAHOMA AGRICULTURE EXPERIMENT STATION; SEMAN, DWIGHT - FORMER ARS EMPLOYEE

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2021
Publication Date: 3/12/2021
Citation: Schomberg, H.H., Endale, D.M., Balkcom, K.S., Raper, R.L., Seman, D.H. 2021. Grazing winter rye cover crop in a cotton no-till system: Soil strength and runoff. Agronomy Journal. 113(2):1271-1286. https://doi.org/10.1002/agj2.20612.
DOI: https://doi.org/10.1002/agj2.20612

Interpretive Summary: Cover crops are grown in the winter to protect soil from erosion and provide biomass to improve soil organic matter. They could provide economic returns to producers if grazed as forage by cattle. Producers concerned about negative impacts from soil compaction following grazing are reluctant to integrate livestock into their cropping systems. ARS scientists from Georgia and Alabama evaluated soil compaction and runoff in a system where cattle grazed a rye cover crop prior to a cotton cash crop. In the fourth year of the study, grazing under wet spring conditions resulted in significant trampling and soil surface roughness. Soil compaction was evident down to 15 cm (6 in) and was still present ten months after grazing. Comparison of runoff from two storm events in 2009, showed lower runoff in the spring from a grazed field compared with a not-grazed field and the opposite response in the fall indicating a temporal response of soil to grazing. Grazing cover crops for short periods under wet conditions appears to present a risk of short-term negative impacts for soils of the southern Piedmont even those with a long history of growing cover crops and use of conservation tillage. This information will be useful to scientists and farmers.

Technical Abstract: Grazing cool season cover crops (CC) could provide an economic incentive to increase cover crop adoption in the Southeast USA if negative impacts on soils can be avoided. Using four small catchments with a long history of cover crops and conservation tillage located in the southern Piedmont of Georgia, we evaluated cumulative and seasonal effects of grazing or rolling a cereal rye (Secale cereale L.) cover crop on soil penetration resistance (PR) and runoff in 2009. Measurements of PR were collected before and after grazing in spring and in winter following cotton (Gossypium hirsutum L.) harvest. Spring grazing under wet conditions created visible surface roughness. Average PR for the 0 to 30-cm profile was 14% greater following grazing compared with rolling the cover crop (1.95 vs. 1.53 MPa). The difference was still apparent the following February (1.86 vs. 1.58 MPa). Significant increases in PR at 2.5 to 7.5 and 7.5 to 15 cm depths were observed for soils in grazed but not in rolled cover crop treatments. A similar pattern was exhibited for PR data summed for the 30-cm profile, where PR increased from March to May in grazed soil and then declined in February. Depth to 2 MPa resistance, considered limiting to root growth, was similar in grazed and rolled cover crop soils in March but was different in May and February and averaged 10.7 cm and 15.6 cm, respectively, across the three dates. Monthly data for 2006 through 2009 did not indicate runoff differences between grazed and rolled CC. Comparison of two specific runoff events for the two adjacent catchments in 2009 showed lower runoff for grazed cover crop in the spring and for rolled cover crop in the fall. These contrasting results appeared to indicate the effects of soil surface roughness and presence of surface cover crop residues were temporally dependent. Our study indicates that grazing cover crops for short periods under wet conditions presents a risk of short-term negative impacts even for soils of the southern Piedmont with a long history of growing cover crops and use of conservation tillage and should be avoided.