Comparison of protected rangeland with improved agricultural lands in generation of runoff and sediment (Case Study: The part of the Mereg river watershed, Kermanshah)

Background and objectives: The soil of rangelands in mountainous areas has always been considered for changing to agricultural land due to its abundant organic matter. Research shows that changing the rangelands and implementing agricultural operations can increase soil erosion and generation of runoff. Therefore, using all kinds of modifiers as a suitable and desirable solution can control soil loss in these lands. This study was conducted with the aim of investigating and comparing the effect of land use change in rangeland and the effect of organic amendments on reducing sediment production, runoff and soil loss in one of the subbasins of Mereg river. Material and methods: The present research was conducted in one of the sub-basins of Merg river, five kilometers away in Kermanshah province. This area is one of the main branches of the Karkhe River and one of the most important subbasin of the Qaresou River. The average annual rainfall is 458.59 mm and the average annual temperature is 13.89°C. Investigating the effect of land use change and organic modifiers (sheep manure and waste compost) on generation of sediment, runoff and carbon loss in both rangeland and agricultural uses, at erosion plots in dimensions of one in two square meters for two years (1398 and 1399) were evaluated. In the first year, samples were collected from undisturbed erosion plots, but in the second year, two modifiers (sheep manure and municipal waste compost) were added to agricultural plots in the amount of 1.5 kg. The modifiers were added  at the ended of July and until the first rain of the autumn season, there was enough time for chemical interactions and influence on the soil characteristics .The samples of runoff and sediment as well as soil samples were analyzed in the laboratory and the volume of runoff, the amount of suspended sediment, the organic carbon percentage of the sediments and the physical and chemical characteristics of the soil were measured. Results: The texture of the soil in both land use was the same (clay loam). But in terms of the amount of organic carbon, the two land uses have a significant difference (at 95 percent level) and this parameter is more than twice as much in the rangeland as in the agricultural use. Based on the results in the first year of sampling, the values ​​of runoff volume, sediment weight, carbon loss during five rainfall events in agricultural were 83, 90 and 87% higher than rangeland. In the second year of sampling, plots located on agricultural lands were treated with soil conditioners and their impact was investigated. Although the use of soil conditioners reduced runoff by 20% and reduced the amount and concentration of sediment in agricultural lands about 31.68 and 13.13%, but the amount of these parameters is still 67, 95, and 72% lower in rangeland use, respectively. The results also showed a 71% higher organic carbon loss in agricultural land use than rangeland. The results of this research showed that the modified wars were successful in reducing soil and water loss, and sheep manure treatment worked better than compost in controlling runoff and sediment.  Conclusion: In general, the results of this research showed that the amendments were able to reduce water and soil loss and sheep manure treatment worked better than compost in controlling runoff and sediment. But none of them have been able to reduce the effect of tillage destruction on this slope as much as rangeland. This shows the role and importance of protecting rangeland in reducing soil degradation and water wastage