Temporal stability of spatial patterns of soil salinity determined from laboratory and field electrolytic conductivity

We elaborated a procedure for the assessment of the temporal stability of soil salinity and the optimization of the sampling effort. Soil electrolytic conductivity data obtained from field electrode probes and laboratory analysis were compared and analyzed to check the temporal stability of salinity patterns. Sampling of 20 locations at different depths was repeated 19 times over a period from November 1994 to June 2001. Both methods showed a strong temporal stability. The Spearman rank correlation confirmed the persistence of the ranking of the different locations. Additionally, using the technique of relative differences, we identified three classes: (1) low saline locations, (2) locations which are representative of the average field soil salinity, and (3) high saline locations. Low saline locations were associated with the zones of waterlogging and/or salt leaching. High saline locations were exclusively in the zone of salt accumulation. Locations representative of the average soil salinity were found in all three possible zones. We investigated how precise the selected locations representing the average soil salinity can estimate this average. We found that using only two locations from the 20 available, the average was adequately estimated with a difference <0.3 dS m(-1). This representativeness was also checked by splitting the measurements into two temporal subsamples. For both subsamples the same locations were representative of the average soil salinity compared to when all measurement dates were considered.