Commercial avocado production in Chile has expanded to areas with poorly drained soils presenting low oxygenation over significant periods of time throughout the year. In many of these areas, irrigation management is difficult because plantations are often placed on slopes of hills. Poorly aerated soils combined with irrigation design and management problems can limit avocado fruit production and quality, particularly if hypoxia stress occurs between spring and the beginning of summer. It is well known that avocado trees are very sensitive to waterlogging and the relatively low productivity of this species may be related to root asphyxiation. Therefore, in order to get adequate yield and fruit quality, proper irrigation management and better soil oxygen conditions in avocado orchards are necessary. The objective of this study was to evaluate the effect of the hydrogen peroxide (H 2O 2) injection into the soil as a source of molecular oxygen, on plant water status, net CO 2 assimilation and biomass of avocado trees established in clay loam soil with water content at field capacity. Three-year-old 'Hass' avocado trees were planted outdoors in containers filled with heavy loam clay soil with moisture content kept at field capacity. Plants where divided into 2 treatments, those with H 2O 2 injected into the soil through subsurface drip irrigation and plants in soil with no H 2O 2 added (control). In addition to determining physical soil characteristics, net CO 2 assimilation (A), transpiration (T), stomatal conductance (g s) and shoot and root biomass were determined for plants in each treatment. Injecting H 2O 2 into the soil significantly increased the biomass of the aerial portions of the plant, but had no significant effect on measured A, T or g s. The increased biomass of the aerial portions of plants in treated soil indicates that H 2O 2 injection into heavy loam clay soils may be a useful management tool in poorly aerated soil.