Carbon Balance of No-Till Soybean with Winter Wheat Cover Crop in the Southeastern United States.

The southeastern United States is an economically important agricultural region, yet its role in the regional C budget is not fully understood. There is concern that climate change, particularly altered precipitation patterns, may induce a shift in how crops exchange CO₂ with the atmosphere. This study examined the seasonal and interannual variation in net ecosystem exchange (NEE) of a winter wheat cover crop (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] using the eddy covariance (EC) method. This was conducted at Winfred Thomas Agricultural Research Station, Hazel Green, AL (2007-2009). Annual C balance ranged from a source in 2007 (NEE = 100 g C m^-2 yr^-1 ) to a sink (-20 g C m^-2 yr^-1) in 2009. Annual ecosystem respiration (RJ ranged between 750 and 1013 g C m^-2 yr^-1, while gross ecosystem productivity was between 650 and 1034 g C m^-2 yr^-1. Seasonal NEE for soybean ranged between 42 and -66 g C m^-2 . The uptake rates from the cover crop (NEE = -80.0, -80.4, and -40.0 g C m^-2 for 2007, 2008, and 2009, respectively) suggested the importance of winter C uptake offsetting C losses caused by summer droughts. The Re varied between 286 and 542 g C m^-2 for soybean and between 160 and 313 g C m^-2 for the cover crop. Annual variations in NEE and Re were primarily due to precipitation and air temperature, respectively, indicating a tight coupling between biophysical factors and C uptake. Our results were compared with those from other reported NEE crop estimates using EC. [ABSTRACT FROM AUTHOR]