ABSTRACT
Energy fluxes at soil-atmosphere and plant-atmosphere interfaces can be summed to zero because the surfaces have no capacity for energy storage. The resulting energy balance equations may be written in terms of physical descriptions of these fluxes; and have been the basis for problem casting and solving in diverse fields of environmental and agricultural science such as estimation of evapotranspiration (ET) from plant canopies, estimation of evaporation from bare soil, rate of soil heating in spring (important for timing of seed germination), rate of residue decomposition (dependent on temperature and water content at the soil surface) and many others. The water balances at these surfaces are implicit in the energy balance equations. The soil water balance equation is different from, but linked to, the surface energy balances; a fact that has often been ignored in practical problem solving. In this chapter the energy balance will be discussed first, followed by the water balance in Section 5.3.
