The carbon and nitrogen storage capacity of soil in two enclosure and grazed ‎sites (Case study: Kote rangelands of Khash City)‎

Background and objectives: One of the most important components of rangeland ecosystems is soil that their degradation will reduce rangeland production capacity. About half of the world's lands are rangelands and they contain more than one-third of the biosphere carbon pool. Therefore, these lands have a high potential for carbon sequestration. This study was conducted to investigate the soil carbon and total nitrogen storage in enclosed and grazed sites in Koteh rangelands of Khash city, Sistan and Baluchestan province. Methodology: To study the effect of enclosure on soil carbon and total nitrogen storage, the 15-year ungrazed site of Kote rangeland located in Khash city was considered, and then a grazed site that was relatively similar to ungrazed site from the aspect of topography and climate was considered as well. According to the topography of the areas, 6 transects with 100 meters' length (three transects in the slope direction and three in perpendicular to the slope direction) were established with approximate distances of 50 meters in each of the enclosed and grazed sites. Three soil profiles were dug from the beginning, middle and end of each transect and soil samples were taken from the depths of 0-15 and 15-30 cm in both sites. Then three soil samples of each depth were mixed together and one composite sample was prepared. Overall, 24 soil samples were transferred to the laboratory in order to measure bulk density, organic carbon and total nitrogen storage. Paired and independent t-test were used to analyze the data in SPSS software. Results: The results of statistical analysis showed that there are significant differences between enclosed and grazed sites from the aspect of both organic carbon and total nitrogen storage (p<0.01). The amount of organic carbon and nitrogen of the enclosed site were higher than that of the grazed site. There was no significant difference between the soil carbon storage of both enclosed and grazed sites at the depth of 0-15 cm, but there was a significant difference at the level of 1% for the depth of 15-30 cm. The highest amount of carbon storage was obtained in the enclosed area at the depth of 15-30 cm (8.1 tons per hectare), while this amount was 5.1 tons per hectare in the grazed site at the same depth. The results of total nitrogen storage showed that there is no significant difference between total nitrogen storage of the enclosed and grazed sites at the first depth, but there is a significant difference between the soil nitrogen storage of both sites at the second depth (p<0.1), so that the total nitrogen storage of the second depth of enclosed site was 0.88 tons per hectare, and that of the grazed site was 0.48 tons per hectare. Conclusion: In general, it can be concluded that enclosure caused an increase in carbon and total nitrogen storage of the enclosed site compared to the grazed. In addition, the amount of carbon and total nitrogen storage of the lower depth (15-30 cm) was more than the higher depth (0-15 cm), and it seems that the amount of organic carbon and total nitrogen storage of desert areas is more in lower depth than upper depth.