Peanut (Arachis hypogaea L.) response to environmental stresses, especially drought, can be dramatic or subtle. Subtle responses may result in significant yield reduction. The objective of this research was to determine the carbon dioxide level that would indicate a peanut plant had entered into a level of stress that resulted in yield reduction. Carbon dioxide exchanges were measured by the eddy-covariance method above a non-irrigated peanut field in Plains, Georgia. The experiment was conducted during the 2006 growing season (19 May-9 October) in order to understand the ecosystem-level carbon budget response to environmental parameters. Results show that ecosystem respiration (R_eco) was demonstrated to be influenced by soil moisture, temperature, and peanut growth stage. In the early growing season, R_eco gradually increased with temperature and was clearly dependent on soil moisture. After initiation of the peanut flowering period, the functional relation of R_eco on temperature was independent of soil moisture. Daytime net ecosystem exchange (NEE) changed significantly with changes in radiation and can be explained by a modified form of the Michaelis-Menten equation. The optimum gross primary production (F_GPP,opt) and  daytime R_eco values, obtained from the Michaelis-Menten equation, were strongly  controlled by soil moisture. The peak F_GPP,opt and daytime R_eco occurred when soil temperature was 28 °C.