Soil Organic Carbon Storage and Greenhouse Gas Emissions in a Grazed Perennial Forage–Crop Rotation System

Abstract

Core Ideas: Perennial forage–crop rotation did not increase soil greenhouse gases emissions compared to annual peanut-cotton rotation. Carbon storage was greater for perennial forage–crop rotation compared to continuous peanut–cotton rotation. Grazing resulted in increased uptake of soil CH4 in some instances. Soils in southeastern United States have lost much of their original soil organic carbon (SOC) as a result of intensive row-cropping systems. One example is an annual rotation of cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) under conventional tillage (CT). Incorporation of perennial grasses such as bahiagrass (Paspalum notatum Flueggé) into the peanut–cotton crop rotation (also called a forage–crop rotation or FCR) can increase SOC storage. Cattle (Bos sp.) grazing on bahiagrass and winter cover crops can improve productivity of the FCR system, but may result in increased greenhouse gas (GHG) emissions. This study evaluates the impact of a grazed FCR on SOC storage and GHG emissions to assess its environmental impact of Coastal Plain soils. A closed chamber method was used to examine emissions of CO2, CH4, and N2O in the FCR. Results indicated that the FCR has potential to increase SOC storage when conservation tillage is used. Grazing of bahiagrass reduced SOC in the 5- to 10-cm depth, but this effect was not observed in the subsequent peanut crop in the rotation following grazing. A moderate stocking rate of 2.5 cattle ha−1 resulted in fewer emissions of CO2 and N2O during seasonal measurements compared with ungrazed management, dependent on location, season, and crop. Flux of CH4 was often negligible; however, grazing increased soil uptake of CH4 in some instances. For the cattle stocking rates used in this study, grazing did not negatively affect SOC storage or soil GHG emissions in FCR systems.