Bahiagrass Impact On Carbon Storage In Coastal Plain Soils Under Peanut-Cotton-Bahiagrass Rotation.

A common crop rotation in the southeast Coastal Plain is an annual peanut-cotton traditional rotation (TR) under conventional tillage (CT).  This system often leaves soil depleted of soil organic carbon (SOC) and susceptible to erosion.  Incorporation of perennial grasses (e.g., bahiagrass) to the TR has been suggested for improving SOC.  The effect of two years of bahiagrass added into the peanut-cotton rotation (i.e., sod-based rotation or SBR) on SOC was evaluated in two trials in Headland, AL, using SOC and carbon isotopic analysis on established (>10 years) SBR and TR systems.  Systems evaluated included: 1) TR under CT, 2) TR under strip tillage (ST), 3) SBR under CT, 4) SBR under ST and 5) SBR under ST with cattle grazing.  In some instances, SOC was higher in the SBR compared to the TR in the top 5 cm, where it ranged from 5.0-7.8 Mg ha^-1 in the TR and 5.1-12.6 Mg ha^-1 in the SBR.  In the top 30 cm, ST resulted in SOC stratification, while SOC was uniform under CT.  Grazing decreased SOC in the 5-10 cm depth under bahiagrass, likely due to reduced root biomass.  The majority of inputs of SOC from bahiagrass (observed to 30 cm depth) were no longer apparent by the end of the subsequent peanut crop.  Cycling of SOC from bahiagrass was clearly demonstrated by isotopic analysis, where bahiagrass resulted in up to 50% SOC, which decreased to as low as 30% SOC after the last cotton phase of the SBR.  Results indicate bahiagrass has the potential to increase SOC, particularly at the surface under ST.  However, peanut digging and cotton stalk removal practices may negate some of this benefit.