WSP03798 - Laserfiche WebLink

Home Browse Search

\~~ ~ '1 ~ ~ drainage waters through blending practices do not protect the usability of our water suppliers for general crop use. Alternative approaches for dealing with the "disposal" of saline agricultural drainage waters should be sought that provide a greater practical benefit from the total water supply thao does blending. Theorv Plants must have access to water of a quality that permits consumption without the concentration of salts~/ (individually or totally) becoming excessive for adequate growth. In the process of transpiration, plants separate nearly pure water from the salt solutions present in the rootzone and the salts are concentrated in the remaining uoused soil water. This water ultimately becomes drainage water. A plant will not grow properly when the salt concentration in the soil water exceeds some limit specific to it under the given conditions of climate and management (Bernstein, 1975). Thus, it is obvious that not all of the water in a supply can be consumed by a plant, if the water contains salt; the greater its' salinity, the less it can be used. A plant expends bio-energy (that would otherwise be used in biomass production) to extract water from a saline (low osmotic potential) soil solution. When a water of excessive salinity for crop production is mixed with a low-salinity water and the blend is used for ' irrigation, the plant essentially removes the low- salinity water from the mix until the fraction of the mix made up of the excessively saline portion is left. This saline fraction is still as unusable (from the plant availability point of view) as it was before mixing. But, in fact, a salt-sensitive crop can not (consume and. hence) concentrate the blended solution back to this point without excessive yield loss, because its' salt tolerance is inadequate in this regard. Thus, a fraction of the low-salinity (previously usable) water used to make the blend is made unavailable for transpiration of salt-sensitive crops as a consequence of blending. Thus diluting excessively saline water with less saline water does not stretch the water supplv for crops of the same or lower salt tolerance. This - "saline water" component is only usable by crops that are more salt-tolerant. Bernstein (1966) indicated that, for any succession of crops, the fraction of maximally used drainage water (the argument applies equally well to any water of high salinity) available for reuse is determined by ./ The term salinity will be used herein in a general sense to mean the preSence of total dissolved salts and/or individual toxic constituents, like boron. . I ~ Rhoades