SURFACE-ENERGY BALANCE PARTITIONING OVER RYE AND OATS COVER CROPS IN CENTRAL IOWA

Evaporation from fields, sub-basins, and watersheds during the fall an d winter period has been assumed insignificant relative to the yearly water balance. The partitioning of surface energy balance components o ver an oat/rye cover crop during the fall and winter periods has nor b een routinely conducted and is not entirely understood The objective o f this study was to evaluate surface energy partitioning over an oat/r ye cover crop and bare soil beyond the? normal growing season. In cent ral Iowa three fields representing an oat and rye cover crop and a bar e soil were instrumented to measure net radiation, soil, sensible and latent heat fluxes using a! Bowen-ratio technique. Monitoring from Oct ober through March was conducted for three years beginning in 1994 and ending in 1997. Results show that energy partitioning at the surface over lye, oats, and bare soil during the fall/winter period is driven by climate, snow, residue cover, and available energy. Seasonal evapor ation totals from mid-October through late-February ranged from 118 to 205 mm for the 3 year study.