Effect of Land-Use Change on some Physical and Chemical Indices of Soil Quality in the Bazoft Region, (Chaharmahal-Va-Bakhtiari Province)

The most important factor in environmental degradation and pressure on ecological resources is rapid population growth combined with unsustainable exploitation of resources. Soil is one of the most important and worthful natural resources of environment. Land use change and deforestation decrease soil quality. Land use change also causes destruction of the evolved soils and decrease soil quality which result in permanent destruction of land fertility. Therefore, studying land use management effects on the soil quality has got an attention in recent years. Destroying the vegetation especially in the last 50 years resulted in important problems like soil erosion, land slide as well as increasing flood in the Bazoft area. In this area, degradation of the forests and their convert to other land uses like pasture, agriculture and urban or rural land use, occurs annually at high extent, in which make high damages to natural resources. In this study, the effect of land use change on soil quality indices in this area located at Chaharmahal-Va-Bakhtiari province was investigated.

In this research, four different managements with relatively similar conditions in terms of the influence of soil producing processes were chosen. Then, 10 composite samples from 0-30 cm depth of each land use (40 samples in total) were taken and different soil properties including soil texture, mean weight diameter of aggregates (MWD), porosity, bulk density, soil acidity, electrical conductivity and calcium carbonate equivalent were determined. One-way ANOVA was used to analyze the dataset. Tukey HSD test was applied to compare the means at the probability level of 5%. The first land use includes the natural forest with predominant cover of Iranian oak and the highest density and cover with the least human interference. Another land use is the degraded forest, caused by deforestation over the last 50 years. The third land use is the agricultural land which transformed from forest land use by deforestation in the last 50 years. The fourth land use is the walnut garden which established from agricultural land about 20 years ago.

The results showed that land use change from natural forest to other uses had a significant effect on most of the studied parameters. The percentage of particle size distribution was affected by different land uses, so that the percentage of clay was significantly higher in the land use of natural forest and walnut orchard than other land uses. The results also showed that the mean weight diameter of aggregates was influenced by the land use change (P <0.001). Factors like soil compaction due to livestock grazing and machinery traffic, agricultural operations and reduced biological activity increased the bulk density in all land uses compared with the forest land use. Deforestation also resulted in 6.92%, 12.05% and 14.16% porosity reduction in walnut orchard, agricultural land and deforestation, respectively. Changing management from farmland to walnut orchards also improved soil porosity by 6 percent. In the study area, the problem of changing vegetation, grazing, planting and other mismanagement increased soil pH in other land uses compared with the forest land use. The comparison of means showed that degraded forest and agriculture land uses had the highest rate of electrical conductivity which showed significant difference with natural forest land use and walnut orchard. Analysis of variance indicated that the land use had a significant effect on calcium carbonate equivalent at the probability level of 0.001. The comparisons also showed that the equivalent calcium carbonate content in agricultural land was higher than the other land uses, and there was no significant difference between walnut orchard and natural forest.

The results of the present study showed that the soil physical and chemical properties were significantly affected by land use change. Overall, it can be stated that the rate of changes in soil quality under human management and different utilization systems indicates failure in sustainable management of soil resources in the study area. Some characteristics such as soil particle size distribution percentage, soil porosity and calcium carbonate equivalent shows that there is no significant difference between walnut orchard and natural forest. However, the walnut orchards can be selected as the best management in areas where it is impossible to restore natural forests. Also, the need for stopping deforestation in Zagros ecosystem is highly recommended.