Soil erosion assessment in tea lands of Nuwara Eliya, Sri Lanka, using the ¹³⁷Cs tracer technique

Abstract

In Sri Lanka, tea is often grown in slopy lands, which increases the risk of soil erosion. This was to assess the erosion status of selected tea plantations during 2022-2023 in Labookellie, Weddamulla and Frotoft estates. For the reference site, nearby montane forest located in Labookellie was selected. Seventy-two soil samples were collected representing two canopy categories (well-grown VP tea and marginal seedling tea) and two slope classes (0-10% and 50 – 60%). At the reference site, cores were sectioned at 5 cm intervals up to 4 cm depth, while study site sampling comprised 40 cm bulk cores. 137Cs activity of soil was measured using a HPGe detector. Soil redistribution rates induced by water erosion were estimated by Mass Balance Model II. Forest area showed a lower soil erosion rate compared to the tea growing areas (p=0.002). Erosion rates were compared using an independent samples t-test, and correlations among parameters were assessed by Pearson correlation analysis. The 137Cs inventory for the forest site was 325 Bq/m2., and it was for tea lands ranged from 72-290Bq/m2 (mean=182.26 Bq/m-2). With increasing slope, erosion rates increased, and the slope category of 50-60% showed the highest erosion rate of 30.51 tons ha-1 y-1 with a sediment delivery ratio of 88% in Labookellie. Marginal tea lands had higher erosion (42.94 tons ha-1 y-1) compared to VP fields in Labookellie (p=0.002). Erosion rates showed negative correlations with organic matter (r=-0.7) and exchangeable K (r =-0.75) contents. Soil erosion in Nuwara Eliya tea lands is significantly influenced by slope and canopy cover.