Root distribution of lychee trees growing in acid soils of subtropical Queensland

Abstract

A core sampling technique was used to investigate the vertical root distribution of 8-10-year-old lychee trees (Litchi chinensis cv. Tai So) growing on 5 acid soils in subtropical Queensland (lat. 27¦s.). At each site, soil and roots were sampled at 10 cm depth intervals to 100 cm, the root density determined and a range of soil chemical and physical properties measured. Eighty percent of the feeder roots were located within the top 0-20 cm (1 site), 0 4 0 cm (2 sites) or 0-60 cm (2 sites). The depth of rooting was greatest in the fine textured soils, while the greatest total root density was recorded in the coarse textured soils. The data suggest that the placement of tensiometers for water scheduling needs to take into account the effective rooting depth of lychee because it may vary with soil type. At all sites, pH values were acidic (pH<6.0) and subsoil pH values were below 5.5, and exchangeable Ca decreased and exchangeable A1 increased with depth. Four of the 5 sites had subsoil with >30% Al saturation of the cation exchange capacity. Although root density (all sites) was correlated with a number of soil chemical properties, stepwise multiple linear regression showed that 62% of the variation in root density could be explained by a curvilinear function of depth. The intercorrelations between soil properties and the correlation of depth with some properties demonstrate the difficulties in separating the effects of depth per se from those of soil properties in reducing root growth.