Multivariate analysis of soil salination-desalination in a semi-arid irrigated district of Spain

Long-term studies of the changes in soil salinity are scarce and most overlook individual ions. Here, we assess changes in soil ionic contents using 42 soils repeatedly sampled during three campaigns over 24 years in a semi-arid irrigated district. Multivariate analysis (MVA) was used to evaluate the spatial distribution of ions and the temporal changes at comparable soil depths in relation to environmental and management factors. In general, the position of the soil in the landscape governed the spatial distribution of the salinity, while the temporal variations were related to irrigation, with incidences depending on the location in the district. Many soils on the slopes and foothills became salinated during the first years due to land leveling, but salination eventually tapered off after sprinkler utilization. At high and middle elevations, most soils were slightly saline in the first campaign but underwent desalination during the study period. At lower elevations, an initial desalination was followed by a pronounced salination, which was attributed to a water table rise with generalized irrigation in the basin. Whereas univariate salinity assessment might lead to conclusions that are over-simplistic at the landscape scale, MVA detects singular behaviors of groups of soils or single cases and has enormous potential coupled with GIS assessment of soil salinity data.