Measurements and Analyses of Surface Energy Balance in Maize Under Limited- and Full-Irrigation.

Estimation of land-surface/canopy evapotranspiration (ET) is essential for quantifying land-atmosphere interaction and crop water use. Latent heat flux can be estimated using the Bowen Ratio (BR) method or as a residual component of the surface energy balance (EB). Practical issues of instrumentation will be discussed, along with theoretical concepts of estimating sensible heat flux, ground heat flux, and net radiation. Field installations include experimental plots (9 m wide) and larger fields (1.7 and 2.2 ha) of full and deficit-irrigated corn (maize) at the Limited Irrigation Research Farm near Greeley, Colorado, USA during the growing season. The BR and EB methods are compared using one season of data from two towers on the larger fields before analyzing the differences between plot data over three seasons. Implications of variable sampling areas, flux planes and lateral advection of energy between treatment areas are recognized. Although an individual plot may not be fully representative of a large field under the same irrigation treatment, sensors measure the actual plot conditions. Thus, estimated differences in ET reflect actual conditions of the experiment. Differences in estimated fluxes between plots will be illustrated. These measurements, energy balances and resulting ET estimates support on-going systems research to address agricultural management effects on crop production with limited water.