Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/2/1996
Publication Date: N/A
Technical Abstract: Surface resistance of agricultural canopies is an important link controlling the exchange of energy between the earth's surface and the atmosphere. However, there is little information on the dynamics of this term and the procedures that could be used for the estimation or measurement of surface resistance. A study was conducted over corn and soybean canopies in central Iowa to evaluate the seasonal changes in surface resistance for different tillage practices and crops. A Bowen ratio system was placed in each field along with soil temperature and surface temperature. These data were used to calculate the aerodynamic and surface resistances for each 30-minute interval. The data were summarized for daily and weekly changes in surface resistance. Surface resistance varied throughout the growing season with the greatest variation in the early growing season and after harvest and fall tillage. At these times the soil surface dominated the energy exchange process. When the canopy covered the soil surface there was little influence of the soil and surface resistance was related to the availability of soil water to the crop canopy. There were differences between the corn and soybean canopies that were related to the aerodynamic properties of the canopy and the response of canopy shape to soil water deficits. The seasonal patterns of surface resistance provide an improved understanding of the dynamics of soil-plant-atmosphere interactions.