Soil textural contrasts can be used to either facilitate or impede water evaporation. In cases where it is used to facilitate evaporation, the cumulative evaporation can significantly exceed the sum of evaporation loss from each individual soil texture. We call this phenomenon evaporation synergy. In brief, when paired columns of contrasting soil textures are exposed at the evaporation surface, soil-water pressure differences move water laterally from coarser media to finer media, which encourages a more rapid development of a dry soil (i.e., mulch) layer on the coarse media. The coarse media now becomes a water reservoir for the fine media.  Because the criteria necessary for synergy to occur is related to the relative hydraulic properties of each media, this phenomenon can only occur when properties of fine and coarse texture are judiciously selected.

How could this be of benefit? A better understanding of the criteria that controls such a mechanism could be very useful to agriculture and ecosystem services. For example, agricultural settings used for dairy effluent application would greatly benefit from higher evaporation rates to reduce both groundwater recharge and potential groundwater contamination. Conversely, evaporation suppression would be of significant value when future food security drives agriculture towards the use of more marginal lands, such as in semi-arid areas where water scarcity determines its marginal status. In this case, well selected finer-textured media used in planting strips amid a coarser textured natural soil would force lateral water movement from the coarser inter-row areas towards the planting strips, while suppressing evaporation. This would permit water harvesting to be done in a more focused and efficient manner.

This presentation addresses evaporation synergy and evaporation suppression by investigating all pairs of the 12 soil textural classes using the Hydrus software package.