Effect of Converting Rangelands to Dryland Farming on Soil Organic Carbon, Case Study: Kurdistan Province

Kurdistan province is dominated by the semi-steppe rangelands and dryland farming is the main land use and therefore the main degradation factor. To determine the effect of rangelands conversion to rain-fed farms on ecosystem carbon stocks, dryland farms and nearby natural rangeland sites (as control) were considered as experimental units. In all experimental units, soil was sampled in depth of 50 cm. Ecological characteristics (soil, topography and climate) in all experimental unites were relatively similar and the only variable was land use. Data analysis was performed using independent t-test and one-way analysis of variance (ANOVA). The results of 114 soil samples analysis showed that there was a significant reduction of soil carbon contents in converted rangelands to dry land farming. The type and intensity of changes depends on planted species and topography. Cultivation of perennial species compared with annual species such as wheat had less negative impact on soil carbon stocks. Abandoned dry land farms were evaluated as the worst kind of land use in terms of the soil organic carbon storage and the average decrease of soil organic carbon was 25 percent. Also the degree of the effect of rangelands conversion to dry land farms on carbon stocks depends mainly on the degree of the slope. As with the increase of the slope degrees, carbon contents of the soil showed great reduction.