Net Carbon and Evapotranspiration Dynamics of Irrigated Cotton Compared to Dryland Cotton.

A significant portion of the intensively cultivated agricultural areas in the United States is located in the Southern Great Plains region of Texas. Once dominated by native shortgrass prairie, the discovery of the vast underground Ogallala Aquifer and its subsequent use for irrigation has transformed this region into the largest producer of cotton (Gossypium hirsutum L.) in the United States. This region is semi-arid, and cotton production in this region is susceptible to periodic droughts. A study was conducted to compare the evapotranspiration and net carbon exchange dynamics of irrigated cotton and dryland cotton in the Southern High Plains. Measurements of carbon dioxide and evapotranspiration fluxes were made using an eddy covariance flux tower.  During the growing season, the evapotranspiration was the highest for the irrigated cotton field. However the irrigated field acted as a net carbon source (38 g C m-2y-1) due to high ecosystem respiration while the dryland field was a net carbon sink (-127 g C m-2y-1).