Black plastic mulch is commonly used in horticultural systems, but it may complicate the sparse crop energy balance by contributing to within-row advection. A steady state, heated foil technique was used to approximate the aerodynamic conductances to heat transport ( g h) of bare soil and black plastic mulch for 33 days. The test site was a field of 0.7 m wide raised beds covered with black plastic mulch and separated by 0.8 m wide strips of bare soil, with no crop present. From numerous point estimates of g h and measurements of the temperature difference between the surface and the air, the sensible heat flux ( H) was calculated independently for bare soil and plastic mulch. Conductance values ranged from 8 to 23 mm s −1 and no difference occurred between the mean g h for mulch (17.0 mm s −1) and that for bare soil (17.8 mm s −1). The H estimated from conductance data was strongly linearly related, in a 1 : 1 ratio, to the H determined by independently solving the energy balance of plastic mulch. The conductance sensor method was used subsequently to estimate H from bare soil ( H soil). Sensible heat from plastic mulch ( H mulch) is the major source of H in the field because it is primarily a function of the net radiation of the plastic. Whereas H mulch was always negative, with daily maxima consistently approaching −400 W m −2, H soil varied between −200 and +50 W m −2 according to surface wetness. Latent heat fluxes from the bare soil were <100 W m −2 when the surface was dry, and up to −400 W m −2 when the surface was wet. Managing the surface wetness of bare soil in a mulched field will not affect the energy balance of the mulch surface per se, but may reduce within-row advection, which is potentially detrimental to seedlings and transplants in plastic mulch systems.
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