『Abstract
Land degradation is the loss in the productivity of land resources
due to many factors, especially soil erosion. Nutrient depletion
and soil organic carbon (SOC) loss are the main impacts of erosion
which not only cause declining crop yield, but also induce off-site
impacts, such as eutrophication and greenhouse gas (GHG) emission.
The main objective of this study was to estimate the depletion
of N, P, K and SOC due to soil erosion prevailing in the three
agro-ecological zones within the Merek catchment, Iran. The erosion
rate and eroded plant nutrients (N, P and K) as well as SOC were
estimated using MPSIAC model. The results showed that the most
important factor affecting land degradation in the Merek catchment
is inter-rill erosion, covering an area of about 20%, which in
turn is promoted by deforestation and overgrazing. The erosion
rate in the agriculture area, rangeland and forest is 14.47, 16.60
and 18.57 t ha-1 yr-1, respectively. The
respective predicted annual N depletion by erosion is 23.5, 26.6
and 32.8 kg ha-1 yr-1 in agriculture area,
rangeland and forest zone, while that of P is 0.230, 0.290 and
0.220 kg ha-1 yr-1. The depletion of K in
agriculture area is 7.01, rangeland is 6.25 and forest is 6.36
kg ha-1 yr-1. The highest loss in SOC is
in the forest with a value of 414 kg ha-1 yr-1
while the lowest is in the agriculture area with a value of 213
kg ha-1 yr-1. The high loss of SOC in the
forest zone is due to serious soil erosion, which is accelerated
by sloping land. It is concluded that the MPSIAC model used in
this study is able to satisfactorily predict soil erosion rate
and the loss of N, P, K and SOC at the catchment scale in the
semi-arid region of Iran.
Keywords: Land degradation; Soil erosion; Soil nutrients; Organic
carbon; MPSIAC model』
1. Introduction
2. Materials and methods
2.1. The study area
2.2. Geomorphological facies map
2.3. The MPSIAC model and its validation
2.3.1. The MPSIAC model
2.3.2. Validation of MPSIAC model
2.4. Soil sampling and analyses
2.5. Calculation of the depleted SOC, N, P and K through eroded
soil
2.6. Statistical analyses
3. Results and discussion
3.1. Dominant erosion features
3.1.1. Inter-rill erosion
3.1.2. Inter-rill with rill erosion
3.1.3. Snow erosion with debris
3.1.4. Gully erosion
3.1.5. Miscellaneous gully-bank erosion
3.1.6. Landslide-piping erosion
3.2. N, P, K and OC levels in the study area
3.2.1. Total nitrogen
3.2.2. Available phosphorus
3.2.3. Exchangeable potassium
3.2.4. Soil organic carbon
3.3. Annual intensity of soil erosion
3.4. Depletion of soil N, P, K and SOC
3.4.1. Depletion of nitrogen
3.4.2. Depletion of phosphorus
3.4.3. Depletion of potassium
3.4.4. Soil OC depletion
4. Conclusions
Acknowledgments
References