Micrometeorology of sprinkler irrigation

Evaporation during sprinkler irrigation involves complex and multiple micrometeorological changes at various stages as the crop canopy is wetted and subsequently dries. The advection of energy is important in this process, particularly with lateral move and centre pivot machines which are used to irrigate extensive areas of cropping and result in a moving patchwork of adjacent wetted and non-wetted areas. To investigate the significance and magnitude of all the terms involved in the energy budget of a sprinkler irrigated crop, a study was conducted on a small area of cotton at the University of Southern Queensland, Australia using eddy covariance and ancillary measurements. The relevant theory is set out and all terms were quantified. Of the ‘minor’ terms in the energy balance, all but the advected energy were shown to be negligible or cancel other terms. The advected sensible heat DH and latent heat DV fluxes were shown to be significant in the energy budget, ranging from 1.5 to 14% of the available energy depending on prevailing meteorological conditions. This advection increased the evaporation from the irrigated area by adding energy (DH) and by removing water vapour (removing energy DV). Of the two terms, neglecting DH would result in a significant underestimate of the available energy for evaporation, and a corresponding underestimate of the actual evaporation. The methodology used, and theory as set out in this paper, provides the means to estimate the additional evaporation that occurs during sprinkler irrigation