Heat transfer, evaporation and carbon dioxide transfer in soil

Abstract

Latent heat flux associated with soil water evaporation connects the surface water balance with the surface energy balance. Soil water evaporation and soil carbon dioxide (CO2) fluxes both involve soil gas transport processes and properties, and both impact the soil environment and physical, chemical, and biological processes occurring in the soil. Accurate and dynamic measurements of soil water evaporation and soil CO2 fluxes enhance the understanding of water, energy, and carbon partitioning at the soilatmosphere interface and the mechanisms of mass and energy movement in the soil. Most previous work focused on measurements made above the soil surface, and quantitative determinations of in situ water evaporation and carbon dioxide fluxes within soil profile were absent. The objectives of this dissertation were to accurately determine transient soil water evaporation and soil CO2 fluxes with depth in bare soil and in different management zones of a corn field and to evaluate in situ measurement techniques. Three-needle heat pulse sensors were used to measure subsurface soil water evaporation at depths of 3 mm and below in a bare field. The daily evaporation estimated from the heat pulse method agreed well with the daily evaporation estimated from Bowen ratio and micro-lysimeter methods. The results showed that heat pulse sensors alone could accurately determine subsurface soil water evaporation with time and depth, and surface and subsurface evaporation could be accurately determined with heat pulse measurements combined with Bowen ratio measurements in a bare field. Newly designed 11-needle heat pulse sensors were used at the following locations within a corn field: within-row (ROW), between-rows with roots (BR), and between-rows without roots (BRNR). The