Spatial Variability of Soil Organic Carbon in Different Hillslope Positions in Toshan Area, Golestan Province, Iran: Geostatistical Approaches

Accessibility to organic carbon(OC) budget is required for sustainable agricultural development and ecosystem preservation and restoration. Using geostatistical models to describe and demonstrate the spatial variability of soil organic carbon(SOC) will lead to a greater understanding of this dynamics. The aim of this paper is to present the relationships between the spatial variability of SOC and the topographic features by using geostatistical methods on a loess mountain-slope in Toshan region, Golestan Province, northern Iran. Hence, 234 soil samples were collected in a regular grid that covered different parts of the slope. The results showed that such factors as silt, clay, saturated moisture content, mean weighted diameter(MWD) and bulk density were all correlated to the OC content in different slope positions, and the spatial variability of SOC more to slope positions and elevations. The coefficient of variation(CV) indicated that the variability of SOC was moderate in different slope positions and for the mountain-slope as a whole. However, the higher variability of SOC(CV = 45.6%) was shown in the back-slope positions. Also, the ordinary cokriging method for clay as covariant gave better results in evaluating SOC for the whole slope with the RMSE value 0.2552 in comparison with the kriging and the inverse distance weighted(IDW) methods. The interpolation map of OC for the slope under investigation showed lowering SOC concentrations versus increasing elevation and slope gradient. The spatial correlation ratio was different between various slope positions and related to the topographic texture.

Effects of Haloxylon spp. of Different Age Classes on Vegetation Cover and Soil Properties on an Arid Desert Steppe in Iran

In arid regions,afforestation has been considered as a method for ecological revival in terms of vegetation enrichment and soil amelioration.In this study,the effects of afforestation with Haloxylon spp.on vegetation cover and soil properties were measured<3,3,6,and 25 years after planting in an arid desert in Iran.Soil samples were collected at two depths(0-30 and 30-60 cm)under and between shrub canopies.Afforestation succession significantly affected plant community characteristics.In total,16 species from 8families and 15 genera were observed along the afforestation successional gradient.Plant species richness and diversity and vegetation cover increased slowly during the succession,and reached the maximum values in the area where Haloxylon had been planted for25 years.Soil nutrient values gradually increased during the succession,and the levels of organic matter,total nitrogen,available potassium,and available phosphorus were significantly higher under Haloxylon canopies than between them.Afforestation reduced soil pH under and between Haloxylon canopies during the succession,while soil electrical conductivity followed an opposite pattern.Haloxylon planting increased the silt content in the 0-30 cm soil layer.Our results suggest that Haloxylon establishment plays an important role in the reestablishment of desertified ecosystems in arid regions.