Assessment of Soil Erosion and Deposition Using Fallout Radionuclide Technique under Different Land Uses and its Relationship with Soil Chemical Properties in the Low Country Dry and Intermediate Zones of Sri Lanka

Although there is a wealth of research findings on soil erosion in the central highlands, there has been meager attention given to soil erosion in the dry and intermediate zones. Therefore, an assessment of soil erosion/deposition under different land uses was conducted in Bathalagoda reservoir catchment in Kurunegala district and Payindikulama tank command area of Anuradhapura district in the year 2019, using Fallout Radionuclide (¹³⁷Cs and ²¹⁰Pb) Technique (FRN) and, its relationship with soil chemical properties was established. Results indicated that, the highest rate of soil erosion in the Bathalagoda reservoir catchment, was under coconut plantation (8.0 t ha^-1 yr^-1). Paddy lands recorded 9.0 t ha^-1 yr^-1 of soil deposition. A high rate of sedimentation of 26.6 t ha^-1 yr^-1 was recorded in the Bathalagoda reservoir, measured using ¹³⁷Cs method. The highest soil available phosphorus (52.5 mg kg^-1) and exchangeable potassium (320.7 mg kg^-1) was recorded under coconut cultivation. In the Payindikulama site, the highest soil erosion of 35.3 t ha^-1 yr^-1 was recorded under shifting cultivation. Paddy lands recorded 6.0 t ha^-1 yr^-1 of soil deposition measured using ¹³⁷Cs method. ²¹⁰Pb method also recorded approximately similar results in both sites. The highest soil available phosphorus was recorded under coconut cultivated lands (47.2 mg kg^-1) and the highest exchangeable potassium was in forest lands (338 mg kg^-1). A highly significant negative correlation exists between soil erosion rate and soil organic matter % in both sites. Moreover, a highly significant positive correlation exists between soil erosion and deposition rates, estimated using ¹³⁷Cs and ²¹⁰Pb methods in both sites. Based on the results, it was concluded that the highest rate of soil erosion occurs under the land use of shifting cultivation. The soil organic matter concentration can be used as an indicator of soil erosion status as evident by high negative correlation between the two parameters.