Geostatistical analysis of soil mechanical properties in Ardabil plain of Iran

This study was conducted to estimate the spatial distribution of penetration resistance (PR), Proctor maximum bulk density (MBD) and critical water content (CWC) as soil mechanical indices. Soil samples to determine sand, silt, clay, organic carbon (OC), CaCO₃, bulk and particle density, total porosity, field water content, MBD and CWC values were collected. Field measurements of PR at 0–10 cm depth were taken from 105 geo-referenced points with 3000 × 3000 m intervals in agricultural lands of Ardabil plain, Iran. Ordinary kriging (OK) and inverse distance weighting (IDW) methods were used to analyze spatial variability of PR, MBD and CWC. The strongest spatial dependences with the lowest ranges of influence were found for OC (7560 m) and MBD (8370 m). The models of fitted semivariograms were Gaussian for PR and MBD, and exponential for CWC. The moderate spatial dependences with the ranges of 13,300 and 40,100 m were found for CWC and PR, respectively. The best prediction according to Lin’s concordance correlation coefficient was obtained by OK for PR (0.48) and IDW for MBD (0.09) and CWC (0.03). These results can be applied in programming of optimum tillage operations for reducing soil compaction risk in the studied region.