Surface conditions effect on energy exchange at the soil surface
Two field studies were conducted to determine the effect of soil surface properties on physical processes occurring at or near the soil surface. Study one examined tillage effects on soil thermal properties and heat flux. Study two examined surface roughness effects on soil reflectance, net radiation, and the partitioning of net radiation;Soil thermal properties were examined after planting in the row zone for three common management systems: moldboard plow, chisel plow, and no-tillage. Soil volumetric heat capacity was not significantly different in the surface 0.15-m depth increment for the three tillage systems. The apparent soil thermal diffusivity, as determined by harmonic analysis of soil temperature data, was significantly greater in the no-till than in the moldboard plow and chisel plow systems. Inasmuch as thermal diffusivity is defined as the ratio of thermal conductivity to the volumetric heat capacity, this implies that soil thermal conductivity was altered by tillage. Thermal conductivity calculated by the line source heat-probe method was at least 20% greater in the no-till soil than in the moldboard plowed soil. Soil temperature was measured and soil heat flux calculated for all tillage systems. The chisel plowed soil was cooler and had a lower soil heat flux amplitude than the moldboard plowed soil. The no-till soil was either warmer or cooler and had a greater or lower heat flux amplitude than the moldboard plowed soil depending on whether the no-till soil was ridge or not. Ridging and crop residue placement in the interrow resulted in a greater soil temperature and heat flux amplitude in the no-till relative to the moldboard plowed soil;Surface soil roughness effects on components of the surface energy balance were examined for a range of roughness conditions. Reflectance of short wave radiation decreased with rougher soil surfaces. Reflectance increased about 25% after the soil surfaces had been smoothed by a 4.7 cm rainfall. Net radiation was increased on the rougher soil surfaces. Soil temperature measured at 0.01-, 0.05-, and 0.15-m depths were higher on the smoother surfaces. Theoretical considerations indicated that the rougher soil surface resulted in a greater latent and/or sensible heat flux.