Winter cover crop is an important component in the southeastern United States sod-based peanut-cotton rotation systems. The objective of this study was to determine effects of previous crops on an oat (Avena sativa L.) cover crop in both conventional and sod-based peanut-cotton rotations. Two cropping systems of Peanut-Cotton-Cotton (Conventional) and Bahiagrass-Bahiagrass-Peanut-Cotton (Sod) with winter oat cover crop were established in an experimental field at the NFREC of University of Florida, Quincy, FL in 2000 and have been continued for investigating long-term soil and crop responses to the cropping systems. In 2007, oat leaf chlorophyll, leaf sap NO₃-N concentration, and aboveground biomass were determined biweekly starting 49 days after seeding (DAS). Oats N uptake was also estimated at 101 DAS (pre-heading stage). Both cropping system and previous crop impacted oat growth and physiological parameters measured. Oats grown in the sod system had higher levels of leaf chlorophyll and NO₃-N and greater biomass and N uptake compared to oats in the conventional system. At 101 DAS, aboveground biomass (4927 kg ha^-1) and plant N uptake (90 kg N ha^-1) of oats grown in peanut plots were much greater than those (3314 kg biomass ha^-1 and 54 kg N ha^-1) of oats in cotton plots. Averaged across previous crops, oats grown in the conventional and sod-based rotations accumulated 61 and 79 kg N ha^-1, respectively.  The increases in cover crop growth, plant N status, and N uptake for the sod-based cropping system were associated with improved soil fertility and other soil parameters.