Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 1998
Publication Date: N/A
Interpretive Summary: The earths surface intercepts solar energy from the sun and partitions it into heating of the earth's surface and evaporation of water. It is generally assumed that evaporation during the fall-winter period is insignificant compared to evaporation during the growing season, however this has not been well documented particularly in the case involving alternative cropping practices using rye and oats during the fall-winter period in central Iowa. Results from this study show that surface energy partitioning over rye and oats cover crops is driven by climate, snow and residue cover. Evaporation totals from mid-October through late February ranged from 118 to 205 mm for the three-year study. No significant differences were found among rye, oats and bare soil evaporation suggesting that during the fall-winter period, evaporation is dependent on water availability, and solar energy and not vegetation response. The impact of this study is that actual continuous measurements of the surface energy partitioning provides the ability to study year-long evaporation patterns as affected by climate and surface cover. This will lead to a better understanding of hydrological water balance issues for winter time periods.
Technical Abstract: The partitioning of surface energy balance components over an oat/rye cover crop during the fall and winter periods is not entirely understood. Measurements of surface energy balance components over oat/rye cover crops during fall and early winter periods in the Midwest has not been routinely conducted. The hydrology of fields, sub-basins, and watersheds during this period has been assumed insignificant relative to the yearly water balance. The objective of this study was to evaluate surface partitioning over an oat/rye cover crop and bare soil beyond the normal growing season. In central Iowa three fields representing an oat and rye cover crop and a bare soil were instrumented to measure the surface energy components of net radiation, soil, sensible and latent heat fluxes using a Bowen-ratio technique. Monitoring from October to March was conducted for three years beginning in 1994 and ending in 1997. Results show that energy partitioning at the surface over rye, oats, and bare soil during the fall/winter period is driven by climate, snow and residue cover, and available energy. Seasonal evaporation totals from mid-October through late-February ranged from 118 to 205 mm for the three year study.