Quantitative and qualitative soil quality assessments of tea enterprises in Northern Vietnam

Abstract

Long-term cultivation of tea (Camellia sinensis (L) O. Kuntze) in the northern mountainous zone of Vietnam has resulted in soil quality degradation that could affect economic development in the region if sustainable production practices are not identified. The objective of the study is to identify appropriate indicators for assessing soil quality on tea plantations. Quantitative (based on soil analysis) and qualitative (based on farmer interviews) indicators were defined based on their sensitivity to change. Key quantitative indicators were organic-C, pH, N, P, K and S concentration (chemical), mechanical resistance, bulk density, total porosity, PAWC (plant available water capacity) and MWD (mean weight diameter) of aggregates (physical), and earthworm populations (biological). Decreases in the organic-C, N, K and S content, pH, total porosity, PAWC, MWD and earthworm populations, or increases in bulk density and mechanical resistance (compaction) indicated a decrease in soil quality due to long-term tea production. Qualitative assessments gathered through farmer interviews were also used to evaluate overall efficiency of current management practices to sustain long-term tea production. Farmers commonly assess soil quality in terms of tactile or visual soil properties. Important indicators based upon farmers’ perceptions were (in order) organic matter, fertility, soil compaction, soil structure, moisture retention, earthworm abundance, erosion, acidity, surface’s thickness and the incidence of weeds. Farmer observations of soil quality changes were generally in good agreement with the quantitative assessments. To ensure adoption of improved management practices, qualitative soil quality information obtained from on-farm surveys should be used to supplement the quantitative data obtained through soil analyses. Key words: Soil quality, indicators, tea cultivation.