Carbon loss in tile drainage and surface runoff from a clay loam soil after a half century of continuous and rotational cropping

Tile drainage and surface runoff are major pathways for pollution of water resources by agricultural nutrients and chemicals. Little is known, however, of the pathways and amounts of carbon entry into water resources from agricultural land. This paper evaluates dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) losses in tile drainage and surface runoff from a Brookston clay loam after more than a half century of monoculture maize (Zea mays L.), continuous bluegrass sod (Poa Pratensis L.), and maize-oat (Avena sativa L.)-alfalfa(Medicago sativa L.)-alfalfa rotation. Water loss in tile drainage and surface runoff accounted for 27%, 32% and 18% of annual precipitation (876-mm) for rotation, monoculture maize and continuous sod, respectively. Tile drainage comprised 66-89% of water loss from rotation and continuous sod, but only 15% from monoculture maize, with the remaining 85% of water loss from monoculture maize due to surface runoff. On an annualized basis, the apparent dissolved C loss was 79 and 83 kg C ha-1 yr-1 from rotation and continuous sod, respectively, while 49 kg C ha-1 yr-1 was lost from monoculture maize. As up to 9% off-gassing loss of CO2 from water samples was measured, total dissolved carbon losses in tile drainage and runoff water were likely greater. For Brookston clay loam soil, leaching into tile drains was the dominant mechanism for dissolved C loss from long-term continuous sod and crop rotation, while surface runoff was the dominant mechanism for dissolved C loss from long-term monoculture maize.