Investigation of on-site implications of tea plantations on soil erosion in Iran using 137Cs method and RUSLE

Tea plantations cover an area of ca. 31,000 ha in the Central North of Iran. This area, after clearing the original forests more than 50 years ago, became exposed to severe soil erosion. The objective of this study was to assess long-term soil erosion rates in tea farms and to evaluate their soil conservation effect at a whole-of-catchment scale. No previous information on direct measurements of soil erosion in this mountainous tea agro-ecosystem of Northern Iran is available. Point-based estimates of net erosion have been obtained using the 137Cs technique and these results were compared with estimates using the RUSLE model. Calculations of soil erosion rates from 137Cs inventories, based on the Mass Balance Model II, revealed that 1.3 mm year−1 and 1.45 mm year−1 of soils were lost from the two sub-catchments A1 and A2, into which the catchment can be divided. The annual net erosion rate of the entire catchment was 17.06 t ha−1 year−1 which is consistent with the rate of 20.4 t ha−1 year−1 obtained by the RUSLE model of at the same scale. This study suggests adopting soil conservation practices to control soil erosion, especially after deforestation and periodic pruning of tea bushes. Sustainable land-use plans are then necessary for tea farms of Iran to protect soil resources and to reduce the off-site impacts of land degradation (mainly siltation) on the reservoirs and coastal area.