Effect of bordering soil surface moisture conditions on evaporation from soybean

Abstract

The latent heat flux ( γE) from a small (e.g. < 0.1 ha) experimental plot may not be representative of that from a large area, due to the effects of dissimilar border surface conditions. This study evaluated the effect of the soil surface moisture conditions of a surrounding 5-ha field of bare soil on the γE from soybeans ( Glycine max. (L.) Merrill cv. Braxton). Soybeans were grown under well-watered conditions in a 10 × 10-m area which surrounded a weighing lysimeter. Hourly net irradiance ( Q n), soil heat flux ( G), and γE were measured for a 43-day period during which the soybean leaf-area index was approximately 4.0 and the bare soil was dry. The soil was then wetted by precipitation (52 mm) and measurements continued for a 4-day period. Means of daily values of the ratio of γE: ( Q n + G) for the dry (−1.93) and wet (−1.34) periods were significantly different. During the dry period, ratio values were proportional to the wind speed. Differences in hourly values of γE and Q n + G were greater in the dry period. These results, which demonstrated a 44% increase in soybean γE when the bordering soil surface was dry vs. when it was wet, affect the interpretation of water-use measurements from small pots bordered by dissimilar conditions.