Emitter selection and operation strategies for drip irrigation based on three-dimensional soil wetting patterns

摘要

Distance between consecutive emitters along the irrigation lateral, and irrigation frequency for trickle irrigation systems, are defined in relation to 3-dimensional soil wetting patterns, obtained from infiltration curves based on a modified Green-Ampt approach. Soil wetting patterns developing under a water surface point source located at the soil surface with unlimited supply, is represented by the time-soil infiltrability distribution function. After an extended period of water supply, soil infiltrability rates usually described for one and two dimensional infiltration; this is a result of the continuous expansion of the hemispherical wetting front, that can offset the effect of diminshing soil water potential gradients on water flow rates inside the wetted soil volume. This consideration may explain the differences in wetted soil volumes obtained under field conditions, when 100 % ETc is provided to a crop on a daily basis, as compared with irrigation events taking place every, third or fourth day. Adjusting emitter discharge to match average soil infiltrability, enables an accurate description of the soil wetting process for the case of a constant discharge emitter. Thus, for different soils and irrigation frequency strategies, soil wetted patterns (maximum wetting depth and wetted radius) can be predicted. Several examples are analyzed to compare wetting patterns and volumes, in order to define more accurately the best: emitter density on the irrigation lateral, application time, emitter discharge, and irrigation frequency, when 100 % ETc accumulated from the last irrigation event is supplied to the crop.