Soil water evaporation and transpiration from a row crop at partial cover

When crops are cultivated in a row configuration, latent heat flux from the soil (LE{dollar}sb{lcub}rm s{rcub}{dollar}) and crop canopy (LE{dollar}sb{lcub}rm c{rcub}{dollar}) influence the energy and water balance of the crop. Field experiments were conducted in Lubbock, TX to examine heat and mass transfer from the soil and canopy separately, in cotton (Gossypium hirsutum L.) under a variety of soil and aerial conditions. Bowen ratio techniques were used to measure the field energy balance. Latent heat flux from the crop canopy (LE{dollar}sb{lcub}rm c{rcub}{dollar}) was determined from stem flow measurements of transpiration. Latent heat flux from the soil (LE{dollar}sb{lcub}rm s{rcub}{dollar}) was calculated as the difference between total latent heat flux (LE) and LE{dollar}sb{lcub}rm c{rcub}{dollar}. These measurements were coupled with radiation measurements at the soil surface to partition the energy balance into soil and canopy components.; The feasibility of computing LE{dollar}sb{lcub}rm s{rcub}{dollar} as a residual was tested by comparing calculated LE{dollar}sb{lcub}rm s{rcub}{dollar} to independent microlysimeter measurements of the soil evaporation. On the average, calculated and measured values of LE{dollar}sb{lcub}rm s{rcub}{dollar} agreed to within {dollar}pm{dollar}11%, provided that stem flow measurements of LE{dollar}sb{lcub}rm c{rcub}{dollar} were normalized on a leaf area basis.; Daily energy balances were strongly influenced by sensible heat transport, and the radiation balance alone did not account for the magnitude or diurnal pattern of Le{dollar}sb{lcub}rm s{rcub}{dollar} and LE{dollar}sb{lcub}rm c{rcub}{dollar}. During dry soil conditions, the canopy absorbed sensible heat from the soil and equilibrium sublayer simultaneously, accounting for over 21% and 12% of LE{dollar}sb{lcub}rm c{rcub}{dollar}, respectively. After an irrigation, LE{dollar}sb{lcub}rm s{rcub}{dollar} accounted for over 50% of LE even when the leaf area index was greater than 2, and 12% to 21% of daily LE{dollar}sb{lcub}rm s{rcub}{dollar} occurred at night.; A one dimensional conceptual model was used to calculate the resistance to heat and vapor transport from the soil and canopy using bulk parameters. Results indicate that the use of a surface resistance to quantify flux from the soil and canopy is viable, and can be related to the intrinsic condition of the surface. Surface and within-canopy aerodynamic resistances were similar in magnitude, and were larger than aerodynamic resistances measured above the canopy.