The effects of soil erosion on nutrient content in smallholding tea lands in Matara district, Sri Lanka

Abstract: Soil erosion is a major problem which is expanding as the natural vegetation is replaced by cultivations. This results in land degradation which decreases the quality and fertility of the soil. Sri Lanka is world leading on the market of tea, with smallholders contributing to an important amount of the production. Tea cultivation in Sri Lanka is highly influenced by the climate and varying topography, factors which also affect the process of erosion. Smallholders in Sri Lanka are very exposed to problems with erosion since much of the natural vegetation has been deforested on the behalf of tea plantations. Since the problem of erosion in Sri Lanka is more well-known in the highlands, the problem is often neglected in the areas of the lowlands even if it is still present. Therefore, this study is important in order to increase the knowledge about the problem and to be able to prevent damages caused by erosion, like the soil losing fertility. This study enlightened the problem of erosion in the lowlands as it was done in Matara district, where the distribution of risks of erosion was analyzed and visualized with GIS. The study aimed to investigate how nutrient content in tea fields were affected by erosion. By measuring the amounts of total organic carbon and total nitrogen, potential variations in fertility in the soil could be estimated. The study raised the question if variations in fertility affected smallholders economically by altering the yield. It was assumed that slope angle in a field would correlate with the grade of erosion. Therefore, soil samples were taken from tea lands with varying steepness to investigate how nutrient content are affected by erosion. Hence, it was in the study stated that nutrient content did not correlate with slope angle. The analyses showed that erosion were not a major threat in the area since the values of total carbon content was homogenous distributed. Still, the values were too high to be reliable. The amount of total organic carbon in the samples varied from 2.46 % to 7.00 % with the mean value of 4.79 %. The analysis of total nitrogen showed that the nitrogen content in the soils had satisfying values. The values had a small range, from 0 % to 0.18 % with a mean value of 0.033 %. The study showed that the yield of the smallholders in the area was not highly affected by variations in nutrient content and therefore probably not by erosion. Even though the study suggests that smallholders in lowlands were not strongly affected by erosion, the problem could still be present if preventing methods are not continued to be used. Erosion is affected by different parameters that vary in importance depending on the geographical location which makes it crucial to conduct more studies of erosion in areas with different conditions to be able to control the consequences.