Investigating Spatial Variability of Soil Quality Indices in Nazar Abad Fields, West of Alborz Province

Information about the spatial distribution of soil quality is one of the most ‎significant issues in recognition, planning, management and optimal ‎exploitation of soil resources in each area. In the this study, the characteristics of soil ‎‎surface (0-30 Cm) were measured in 95 fields in the Nazar Abad region in Alborz ‎province and the factors influencing soil quality were selected using ‎principal component analysis (PCA) method. In addition, the weighted additive soil quality index (SQIw), the additive soil quality index (SQIa) and the Nemero soil quality index (NQI) were determined using total data set (TDS) and minimum data set (MDS). Spatial variability of these soil quality indices were analyzed using geostatistics technique and their spatial distribution were determined using the Ordinary kriging method‎. Based on the results and among the soil quality indices, the SQIw obtained from the MDS, had a higher accuracy in the area with R2 of 0.89, mean absolute error (MAE) of 0.11 and normalized root mean squares error (NRMSE) of 0.1. The exponential variogram model (R2 = 0.95) indicated that the SQIw and SQIa indices using MDS had the best fitness, whereas, the spherical model (R2= 0.90) was strongly fitted to the NQI index obtained from MDS. Furthermore, the effective range of spatial variability for SQIa, SQIw and NQI indices was 8, 10 and 11.5 kilometers, respectively. Soil quality of the fields in the area was strongly related to the soil particles size distribution, especially sand and clay percentages with coefficients of 0.90 and 0.85, respectively. Soil quality value in the area decreased considerably from west to east. This study revealed that the geostatistics technique can be used for spatial analysis of soil quality indices in the area and spatial distribution maps of these indices can be effectively used to plan the sustainable soil management strategies in the fields.