Drainage effects on spatial variability of soil electrical conductivity in a vertisol

Spatial variability of soil electrical conductivity (EC) is characterized in a 33 ha plot before and 2 years after drainage initiation. Measurements of EC were made in a square grid at 50 m spacing and at 0–20, 20–40, 40–60 and 0–60 cm depths. Both mean EC values and coefficients of variation (CV) are reduced after drainage. The frequency histograms show that EC fits to a lognormal distribution before drainage, whereas it seems to be normally distributed after drainage initiation. The bimodality found in histograms before drainage was not observed after it. Spatial structure of soil EC is strongest at 0–20 cm before drainage and it is weaker at greatest depths. Nevertheless, the semi-variogram at 40–60 cm after drainage shows a more remarkable spatial structure. EC spatial variability shows anisotropy before drainage, which was related to topography. However, directional semi-variograms after drainage did not show such anisotropy. In conclusion, drainage not only reduces EC values, but also notably changes EC spatial variability.