Surface energy balance of a corn residue-covered field

Abstract

Crop residues on the soil surface have the potential to significantly affect the magnitude of individual components of the surface energy balance. Previous research has concentrated on residue effects on soil temperature and moisture early in the growing season. The objective of this study was to measure each of the surface energy balance components of a field during snow-free periods between successive growing seasons. A Bowen ratio system was used to measure surface fluxes within a no-tillage corn ( Zea mays L.) field near Ames, IA, USA. During the fall, large solar zenith angles and short daylengths resulted in <5.1 MJ m −2 d −1 of available energy ( R n− G). On overcast days with a dry surface, average daytime Bowen ratios ( β) were <1.5 and 42% to 75% of the available energy was consumed by evaporation. On contiguous sunny days, daytime β values were >2.3 and <21% of the available energy was partitioned to evaporation. When the surface was wet, there was little difference in average daytime β values (1.0 and 1.5 on sunny vs. 0.87 and 1.84 on overcast days) while less available energy was used to evaporate water on sunny days (<19% vs. >38% on overcast days). More energy was available (up to 12.9 MJ m −2 d −1) during the spring measurement interval with daytime Bowen ratios averaging 1.7 and 0.8 on sunny and overcast days, respectively. With overcast conditions and wet soil, evaporation approached potential rates predicted by both the Priestley–Taylor and Penman–Monteith equations. With clear skies and wet soil, Penman–Monteith estimates using a residue resistance term agreed well with measured values.