Energy Balance of Irrigated and Dryland Cotton in the Southern High Plains.

Cotton (Gossypium hirsutum) is a major crop in the Southern High Plains that is produced under both irrigated and dryland cultures. In 2008, the energy balance components (net radiation, soil heat flux, sensible heat flux, and latent heat flux) were measured at Bushland, Texas. Four precision weighing lysimeters (each containing a 3 m x 3 m by 2.3 m deep soil monolith), each located in the middle of 2.4-ha fields in a block pattern, were used in the study. Two lysimeter fields were irrigated and the other two were un-irrigated (dryland). The north fields of both the irrigated and dryland fields had N-S oriented rows while the south fields of both the irrigated and dryland fields had E-W oriented rows. Latent heat flux was measured using precision weighing lysimeters and compared with estimates from Bowen ratio and eddy covariance methods. Convective sensible heat flux was measured with Bowen ratio, eddy covariance, and the residual energy balance component from the lysimetry data combined with radiometry (for net radiation) and soil calorimetry (for soil heat flux). The results will compare the latent heat fluxes measured with the three methods and the convective sensible heat fluxes measured with the two micrometeorological methods with the residual convective sensible heat fluxes from the lysimeters. Energy balances in both dryland and irrigated cultures will be summarized and discussed.