Long-term changes in spatial variation of soil electrical conductivity and exchangeable sodium percentage in irrigated mesic ustifluvents

• The determination of soil salinity and sodicity changes from 1966 to 2008 was aimed.
• Soil salinity and ESP were measured in 1966 and 2008.
• Geostatistics methods were used to analyze spatial variability of soil properties.
• The soil salinity and sodicity decreased in 42 years.

Soil salinity and sodicity obscure growth of many field and horticultural crops. Spatial and temporal variations of these attributes should be known to avoid their impacts on plant growth. We studied long-term changes in spatial variation in soil electrical conductivity (EC) and soil exchangeable sodium percentage (ESP) in 8186 ha Bafra plain, located in Middle Black Sea region of Turkey. Data collected in 1966 and 2008 were evaluated and compared by geostatistical and GIS techniques. Semivariograms for EC and ESP were calculated and graphed for 0–30, 30–60, and 60–90 cm depths for both sampling times and complementary kriging prediction maps were built. Both EC and ESP decreased from 1966 to 2008 in acreage and severity in all three studied depths. The EC values ranged from 0.32 to 22.61 dS m−1 in 1966 and from 0.51 to 7.38 dS m−1 in 2008, and ESP values ranged from 12.8 to 76.0 in 1966 and from 9.77 to 40.71 in 2008. In both sampling times, increasingly greater values of EC and ESP occurred by depth. In 1966, 3181 ha of study area had a severe salinity and sodicity problem, while this acreage decreased to 548 for salinity and 2128 ha for sodicity by 2008. Soil EC above threshold level (4 dS m−1) decreased considerably from 1966 to 2008, and this decrease was attributed to that irrigation and complementary drainage removed excess salts away from the soils. Soil ESP decreased to below threshold value of 15 almost in entire area for 0–30 soil depth while it remained over threshold value in 30–60 and 60–90 cm soil depths in eastern part of the study area. A multivariate analysis along with geostatistical analysis can aid to evaluate impact of soil management and land use change on soil EC/ESP as well as soil variables having correlations with EC and ESP.