Observations on kiwifruit (actinidia chinensis planch) root exploration, root pressure, hydraulic conductivity, and water uptake

The rooting patterns of mature kiwifruit (Actinidia chinensis Planch.) vines were observed in 2 soils of contrasting texture — Ohinepanea sand and Levin silt loam. Near the surface of both soils, roots extended laterally 2.2-2.4 m from the base of the stem. In the Bay of Plenty, rooting depths of 3 m have been observed and in the Ohinepanea sand significant moisture extraction occurred to depths exceeding 2.4 m. By contrast, the roots in the Levin soil were restricted to the top 70 cm because of unfavourable subsoil conditions. Some hydraulic characteristics of kiwifruit were measured and provided a basis for examining the relative contributions of plant and soilto- root resistances in the water uptake process. Large xylem vessels up to 0.5 mm in diameter in both roots and stem provide a very low resistance pathway for water movement within the vine. The measured hydraulic conductivities, which varied between 2.7 and 7.2 X 10^-7m²/Pa per s, may be the highest ever reported. Positive root pressures of 20 kPa were also measured and used to estimate the effective soil-root conductance for active uptake. These results imply that most of the root surface is capable of participating in water uptake and that if water is to remain nonlimiting under peak evaporative demands then the soil must be maintained at high water potentials.