Spatial Distribution of Soil Quality in Savojbolagh Fields in Alborz Province

Knowledge on the spatial distribution of soil quality is one of the most ‎important issues in recognition, planning, management and optimal ‎exploitation of soil resources. In this study, physical, chemical and biological properties of topsoil ‎‎(0-30 cm) were measured in 50 fields (1650 m × 1650 m) in Savojbolagh region, Alborz ‎province. All of the factors influencing soil quality were selected using ‎the principal component analysis (PCA). The Weighted Additive Soil Quality Index (SQIw), the Additive Soil Quality Index (SQIa) and the Nemero Soil Quality Index (NQI) were quantified using either the total data set (TDS) or the minimum data set (MDS). Spatial variability of these soil quality indices were analyzed using geostatistical technique. In addition, spatial distribution of them were determined using the Ordinary Kriging method‎. The results showed that for the NQI index, the best fitted model was the Gaussian (R2= 0.93) when MDS was used, whereas, the exponential (R2= 0.79-0.99) model was strongly fitted to the other indices obtained from MDS and TDS. Furthermore, the effective range of spatial variability for SQIa, SQIw and NQI indices was 6-6.2, 2.7-3.65 and 4.5-7.2 kilometers, respectively. The NQI obtained from the TDS appeared to have the higher accuracy in the area (R2= 0.85, normalized root mean squares error (NRMSE) = 0.01). A large part of the area has high quality (class II) as well as to some extent areas have medium quality (class III) and very high (class I). Soil quality indices in the region were in moderate spatial dependence (0.31-0.7). So, the soil quality in the region is affected by both natural and external factors. Therefore, regarding the low organic matter as well as the weak structural stability of soil in the study area, one may expect that by implementing appropriate management methods such as adding organic matter, the soil quality will be increased.