Application Efficiency v Salinity

There is some discussion in Australia at the moment about the effect of high application efficiency on soil salinity. Some people argue that high application efficiency, for example with Drip irrigation systems, leads to lower leaching volumes and less salt removal, therefore a gradual increase in soil salinity over time.On the other hand, less efficient application methods such as flood irrigation or poorly designed or maintained sprinkler systems presumably lead to higher leaching volumes, and removal of salt by this argument.

This argument seems flawed to myself and my colleagues, we would argue that the more efficient system leads to removal of the same amount of salt using less water for drainage, assuming that you supply sufficient water to generate drainage.

Is there anyone who has conducted any research in this area, and can give an informed opinion on the question. The argument is not directly about pressurised vs flood irrigation, but about the effect of increasing application efficiency on soil salinity and salt leaching. Is there a simple formula that relates to the above.

Denis Sparrow

In a water balance study of a 150 ha RedCliffs (Vic.) catchment we found an average 30 % of water applied was draining (into your drinking water). There was no salinity problem in the catchment however some 400 t of salt
were being exported annually.

We then used a crop/soil water model to ask the question "How much can the irrigation application amount be reduced and still maintain a constant, non yield limiting soil EC (~1 dS/m) ?". The model predicted a 10% leaching
fraction would fit this situation and agreed with your assertion that the same amount of salt was being exported, just more concentrated.

These results are in a report (NRMS SIMPET project) which Tony Meissner has.

Philip Charlesworth

I would like to quote a statement from page 35 of American Society of Civil Engineers (ASCE) Manuals and Reports on Engineering Practices No. 71 - Agricultural Salinity Assessment and Management, pg. 619, 1990, ISBN 0-87262-762-4.

"Drip irrigation, if properly designed, minimizes salinity and matric stresses because the soil water content is maintained at a high level and the salts are leached to the perimeter of the wetted volume, where rooting
activity is minimal. Drip irrigation is usually the method of choice when the water is high in salts, though the high build-up of salts in the fringe of the wetted area may eventually become a problem."

Pages 34-36 discuss generalities by irrigation method. The manual is an excellent reference and highly recommended for individuals desiring more information on the subject. Information on ordering is available at: http://www.asce.org/ under publications.

Thomas L. Spofford

One particular aspect to the question of salinization vis a vis method of irrigation is flood irrigation on alluvial soils.

In the El Paso Valley, Seichii Miyamoto showed that salt build up was in large due to variations in soil texture within laser-leveled basins. Water was selectively perculating through the courser soil; the parts of the basin comprised of more clay experienced less infiltration, thus less leaching, and eventually go to the point that enough salt was built up to kill the pecan trees in those areas.

An SDI system (and sprinklers for that matter) would be more of a point source and would get around the problem of uneven infiltration/salt leaching.

Joe Henggeler