Water balance of tropical eucalypt plantations in south-eastern China

Abstract

Monthly, seasonal and annual water balances of Eucalyptus urophylla plantations on the Leizhou Peninsula, southeastern China were estimated in 40 m×40 m plots at two sites with contrasting soil types. The Jijia site is located on basalt-derived clay rich soils, while the Hetou site is characterised by coarse textured soils formed on Quaternary sediments. Observations of evaporative processes (overstorey canopy interception and transpiration, and soil evaporation), soil moisture dynamics, and climate variables were collected at both sites over 2 years. Canopy interception was measured by throughfall troughs and stemflow collectors, daily transpiration was measured by the heat pulse technique in year 1 and estimated from regressions with potential evapotranspiration and available soil water in year 2, soil evaporation was measured by periodic microlysimetry and used to derive a daily soil surface resistance—matric potential relationship for estimation of daily soil evaporation throughout the study period. Soil moisture storage was measured to 4 m depth and drainage estimated as the residual term in a water balance equation. Total annual evapotranspiration ( E t) was similar at 1118 and 1150 mm at Jijia and 969 and 1024 mm at Hetou for years 1 and 2, respectively, despite 20–30% higher rainfall in year 2. These values represent 71 and 66% of annual rainfall in year 1, and 54 and 50% in year 2. Transpiration did not exceed 600 mm in either year and annual soil evaporation was 15–26% of E t, with the higher values from Jijia. The higher rainfall in year 2 was predicted to produce an increase in drainage and runoff rather than tree water use. Dry season water balances showed E t exceeded or approached rainfall, indicating water use from deep soil or ground water storages following soil water depletion, particularly at Hetou. However, storages were replenished by high wet season recharge. The differences in soil properties between the sites resulted in a three-fold greater soil water store at Jijia that provided a supply for E s, and the sandier Hetou soils with poor water holding capacity had greater wet season drainage and higher dry season abstraction from deep storages. The water use of the eucalypts does not appear to be seriously deleterious for water supply in this area.