ROOT WATER-UPTAKE BY KIWIFRUIT VINES FOLLOWING PARTIAL WETTING OF THEROOT-ZONE

Rates of sap flow and root-water uptake by two 7-year old kiwifruit vi nes (Acinidia deliciosa) were studied in an orchard with the aim of de termining the ability of the vines to alter their spatial pattern of r oot-water uptake following differential wetting of the root zone. Time -domain reflectometry (TDR) was used to monitor changes in the soil's volumetric water content, theta. The heat-purse technique was used to monitor sap flow not only in the stem but also in several large roots to see how root flow responded with local changes in soil water availa bility. Prior to irrigation there was a broad correspondence between t he pattern of water uptake and the distribution of root-length density . However, following irrigation, we observed a preferential uptake of water from the wetter parts of the soil and a corresponding decline in water uptake from the drier parts of the soil. Observations of root u ptake by TDR following irrigation also revealed the inordinate activit y of near-surface roots. The vine would preferentially draw upon near- surface water if it were available. Kiwifruit vines are able to shift rapidly their pattern of uptake, in a matter of days, away from drier parts of the root zone and begin to extract water preferentially from those regions where it is more freely available. Upon full wetting of the root zone, previously inactive roots in the dry soil of the root z one were quickly able to recover their activity. Indeed their activity following rewatering was found to be greater than it had been prior t o the period of soil dryness. A rapid flush of new root growth is cons idered to be the mechanism that leads to this enhanced activity.