Geostatistical analysis of soil total porosity and available water content in range lands of eastern Sabalan

In this study, the spatial variability of soil total porosity (n) and available water content (AW) were investigated in the range lands of eastern Sabalan, Ardabil Province, Iran. Soil sampling (n=98) from 0 to 30 cm depth was regularly done in 200 × 200 m2 grid and the position of points was recorded with Global Position System. Total porosity was calculated using soil bulk and particle density variables and AW was computed from field capacity and permanent wilting point soil moisture coefficients. The ratio of nugget effect to sill showed that AW (0.001) and n (0.36) variables had strong and moderate spatial structure , respectively. The range of influence for n and AW variables was obtained 807 and 483m, respectively. The exponential model was the best experimental semivariogram for both variables. According to the mean absolute error (MAE) and mean bias error (MBE) criteria, kriging method estimated better than inverse distance weighting (IDW) method for n. The IDW method had higher accuracy in estimating AW relative to kriging method. The spatial variability maps represented that the soil available water content is low (AW= 0 to 0.18 g g-1) because of high sand (11.86 to 99.52%) and low content of organic carbon (0.10 to 2.45%) in the range lands of eastern Sabalan.

Keywords:

range lands , soil water content , geostatistics , kriging