SOIL ORGANIC CARBON AS AN INDICATOR OF SOIL QUALITY: A STUDY IN SELECTED TEA PLANTATIONS IN GALLE DISTRICT

Abstract

Assessment of soil quality in tea lands is important to determine the extent ofdegradation and introduce sustainable land management practices. A study wasundertaken in two stages to assess the suitability of soil organic carbon as a soil qualityindicator in tea lands. Soil samples were taken from 0-15 em tea estates in the GalleDistrict of Sri Lanka. In the first stage, soil samples were depth from selected taken from15 locations under four different field categories viz., under rehabilitation, rehabilitationcompleted, planted tea following rehabilitation and planted tea without rehabilitation.Second stage involved sampling of a tea field under rehabilitation and tea fields ofvarious ages (3, 7 and 11 year old) situated at one location. Soil samples were also takenfrom two forest sites to assess the impact of cultivation on soil organic carbon. Bulkdensity was measured at the field and soil samples were analyzed for total organiccarbon.

Results revealed that land management has a significant impact on the quantity of soilcarbon in tea plantations. While rehabilitation process has increased the soil carboncontent, nearly 15% of the added carbon is lost during the initial years after planting tea.Forest soils had a soil organic carbon (in the O-15cmsoil layer) range of 3.39 to 4.42 kgm·2 compared to 3.02 to 3.18 kg m-2 observed in rehabilitated tea lands. The l l-year oldtea field has lost over 40% of its soil organic carbon since rehabilitated and planted withtea. Soil organic carbon can be considered as a robust indicator of soil quality and moreresearch is required to establish critical levels of soil carbon for tea lands in differentstages of the cultivation-rehabilitation cycle