بررسی عوامل فیزیکی موثر در تخریب خاک در آزمایشگاه ثابت فرسایش

Soil degradation is one of the greatest challenges for human societies, because soils are the excited skin of the earth where the atmosphere, hydrosphere, biosphere and pedospher, meet and intersect. Soil is a basis for producing food and fibre, providing a foundation for structures, and recycling waste materials. Growing population, particularly in the third world, has increased the demand for food, fibre, fuel and animal feed. The expansion in agriculture in order to meet these requirements combined with the increasing range of other human soil disturbing activities has led to an acceleration of soil degradation. Soil degradation can be defined as a loss or reduction of soil energy. It can be also said that soil degradation is equal to reduction in soil functions or soil uses. Based on this approach it is possible to distinguish between natural soil degradation and soil degradation caused by anthropogenic activities resulting from various types of land use change mostly associated with agricultural activities. The aim of this project is mainly to investigate the physical parameters affecting soil degradation using rainfall simulator in a stationary erosion lab. The most important physical aspects of soil degradation are soil erosion, soil aggregate breakdown, reduction in the stability of aggregates, sealing and crust processes and soil compaction. The project mostly focused on soil erodibility parameters and their relation with soil characteristics such as aggregate stability in one hand and the other hand aimed to evaluate the effect of rock fragments on soil erosion and sedimentation using a tilted flume and rainfall simulation facilities. Nowadays numerous approaches were developed to predict soil loss, which some of them are process-based models and others are empirical. Soil erodibility parameter is one of the intrinsic characteristics of soil used in erosion models to estimate soil loss. Many researchers have attempted to find the relationship between soil characteristics and erodibility factor to show which soil properties are represented for soil erodibility factor. Since waterstable aggregates are most likely responsible for the most of physio-chemical characteristics of soil, in this study we tried to investigate the relationship between soil erodibility factors and some soil characteristics indices such as MWD and WSA to represent the soil sensitivity to erosion. This paper reports the study carried out in the Research Institute of Forests and 85 Rangelands Erosion Lab. The aim of the paper is to compare aggregate stability indices with conventional erodibility factor sued both in empirical and process-based models of soil erosion, using small scale flume and rainfall simulator. Regarding the erodibility parameter, it was found that estimation of sediment yield using ? erodibility from the GUEST model of erosion fitted better with measured sediment when compared with sediment estimated by MUSLE and Richardson using K factor. Keywords: Erodibility factor, water-stable aggregate, stability indices MWD, simulated rainfall, soil erodibility, stone cover, rock fragments, Process based-models and Empirical models