Assessment of Soil Erosion Under Different Land Uses in Nalanda Reservoir Catchment and Kuruwita, Kaluganga Sub Catchment Using Nuclear Techniques

Soil conservation act No. 25 was enacted in the year 1951 by Sri Lankan government to mitigate the consequences of soil erosion in the Central highlands. However, lack of catchment scale soil erosion data in different land uses is a serious limitation in successful implementation of the soil conservation act. Therefore, experiments in two contrasting agro-climatological regions of Low country Wet Zone (Kuruwita in Rathnapura district) and Mid Country Intermediate Zone (Nalanda in Matale district) were conducted to find out the rate of soil erosion/deposition in different land uses using two fallout radio-nuclides (137Cs and 210Pb). Relationships among soil chemical properties and the rate of soil erosion/ deposition were computed. According to the results, land uses of shifting cultivation in Nalanda and tea cultivation in Kuruwita recorded the highest rate of soil erosion. Net soil deposition was observed under paddy cultivation in both sites. The highest soil nutrient availability was observed in paddy fields in Nalanda, but, tea fields in Kuruwita. Correlation analysis revealed a significant positive correlation between two radio-nuclides employed in determining soil erosion/deposition rate and between soil available phosphorus and exchangeable potassium in both sites. Based on results, it was concluded that both 137Cs and 210Pb can be utilized in assessing soil erosion and sedimentation. Among the land uses tested, shifting cultivation is highly contributing to soil erosion and paddy fields are acting as a sink to eroded soils from other land uses.