Effect of Row Orientation On Energy Balance Components.

Solar irradiance is the primary source of energy that is converted into soil, sensible, and latent heat fluxes in the soil-plant-atmosphere continuum.  The row orientation of agricultural crops relative to the sun’s zenith angle determines the amount of solar irradiance reaching the plant and soil surfaces and its partitioning via absorption and reflection from soil and vegetation.  Row orientation also affects soil heat flux and evaporation.  Since soil evaporation may be considered as a non-productive water loss, minimizing soil evaporation improves water use efficiency.  To assess the potential for water conservation, quantitative determination of soil evaporation relative to total evapotranspiration is required.  As part of a large scale experiment conducted in a cotton row crop in the Texas Panhandle, USA, extensive state-of-the-art micrometeorological measurements were undertaken.  Experimental setup included measurements across the interrow space in two fields with perpendicular row orientations.  Results showed that row orientation influenced the diurnal pattern of soil heat flux, and that wind direction relative to row orientation regulated the amount of soil evaporation. Therefore, the overall energy balance and water use efficiency of a row crop is influenced by complex interactions between row orientation and meteorological variables. Row orientation should be accounted for when modeling the soil-plant-atmosphere continuum and may be an important management strategy for maximizing crop water use efficiency.