Influence of Bahiagrass in Rotation with Peanut and Cotton On Carbon Storage in Southeastern US.

A traditional cropping system in the Southeast US is an annual rotation of cotton and peanuts under conventional tillage.  This cropping system contributes to erosion and loss of nutrients in the soils of this region.  Incorporation of perennial grasses (e.g., bahiagrass) to this rotation has been suggested to improve soil organic carbon (SOC), particularly in conjunction with conservation tillage practices.  Grazing of livestock provides another mechanism to maintain and recycle SOC and nutrients.  To determine the effect of perennial grasses and grazing activities on carbon sequestration in a peanut-cotton rotation, SOC and its isotopic composition were evaluated on established (>10 years) crop rotation systems.  Systems evaluated included 1) peanut-cotton under conventional tillage, 2) peanut-cotton under strip tillage, 3) peanut-cotton-bahia-bahia under conventional tillage, 4) peanut-cotton-bahia under strip tillage and 5) peanut-cotton-bahia-bahia rotation under strip tillage with cattle grazing.  Total C was evaluated over a 3 yr interval to determine the influence of bahiagrass and grazing on SOC storage in the established systems.  In addition, degradation of SOC and the isotopic ratio of ¹³C/¹²C were evaluated to assess the contribution and recalcitrance of bahiagrass to SOC.  Results indicated no difference in total SOC between the rotational systems; however, bahiagrass contributed up to 45% of the C in the peanut-cotton-bahia-bahia rotations.  Isotopic analysis indicated that C from bahiagrass was cycling during the rotation as it was lowest at the onset of the first year of bahiagrass and highest following two years of bahiagrass.  The effect of the bahiagrass on SOC was found to a depth of 15-30 cm.  Use of a moldboard plow resulted in a more homogeneous distribution of bahiagrass C compared to strip tillage, but cattle grazing had no effect on C storage resultant of bahiagrass.