Assessing long-term effects of Tea ( <i>Camellia sinensis</i> ) cultivation on soil quality in highland agroecosystems: a case study in Lam Dong, Vietnam

Abstract. Long-term monoculture systems such as tea (Camellia sinensis) plantations can lead to significant changes in soil quality, directly influencing crop productivity and sustainability. This study investigates the impacts of tea cultivation over a 20-year period on key soil quality indicators in Lam Dong province, Vietnam – a major highland tea-growing region. Soils were sampled from plantations of varying ages (5, 10, and 20 years) and compared with native forest soils. Chemical, physical, and biological properties were assessed, including soil organic carbon (SOC), nutrient availability (N, P, K), pH, bulk density, plant-available water capacity (PAWC), aggregate stability, and earthworm populations. Results show a significant decline in SOC, available P and K, and PAWC with increasing plantation age, while bulk density and mechanical resistance increased, indicating progressive soil compaction. A multiple regression analysis revealed that SOC, available P, total K, and PAWC were the most predictive indicators of long-term tea productivity. Cost-benefit analysis suggested that tea cultivation remains marginally profitable after 20 years, provided that adequate fertilization is maintained. This study proposes threshold values for soil quality indicators to support sustainable tea production in tropical highland systems.