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5 Estimating the Extent of Saline Areas, Monitoring Change
and Predicting Its Future Extent
5.1 Estimating the Extent and Change of Existing Salt-
Affected Land
Salt-affected land has been identified and mapped in a number of ways throughout
the world.
5.1.1 Surveying Landholders
Surveying landholders can provide an approximation of the extent of dryland salin-
ity provided there is a common understanding of what constitutes secondary salin-
ity. Surveys were carried out about every ten years in Western Australia until 2002
when the process ceased (Fig. 2 ). Over time, landowner’s knowledge of what was
primary salinity was lost, and accurate attribution of the yield losses to salinity was
uneven between observers, impairing the value of the survey.
5.1.2 Aerial Photograph Mapping
Salt-affected land usually has poor vegetative cover (and a salty surface crust when
severely affected) or contains indicator species such as halophytes. However as
mentioned previously, salinity is often associated with waterlogging, sodicity and
poor soil structure (hard-setting soils) which complicates what is being mapped as
dryland salinity. Removing waterlogging and inundation (surface ponding) as a
Fig. 2 Estimates of the extent of dryland salinity as assessed by surveying Western Australian
farmers
D.J. McFarlane et al.