VARIATION IN PLANT AND SOIL WATER RELATIONS AMONG IRRIGATED BLUEBERRY CULTIVARS PLANTED AT TWO DISTINCT IN-ROW SPACINGS

Abstract

A study was conducted to determine the effect of in-row spacing on plant and soil water relations in 'Duke', 'Bluecrop', and 'Elliott' highbush blueberry (Vaccinium corymbosum L.) and to identify possible mechanisms that may enhance the ability of these cultivars to tolerate short-term soil water deficits. Changes in soil water content, stem water potential, and leaf stomatal conductance were measured 4 years after planting on well-irrigated plants of each cultivar spaced 0.5 or 1.2 m within rows on raised beds (~0.3 m high) and 3.0 m between rows. Irrigation (711 mm) was applied equally to all treatments by overhead sprinklers during the dry summer months from mid-May to early-September. Close spacing significantly reduced individual shoot dry weight, but also significantly increased crop light interception and water uptake from 0-0.6 m soil depth compared to plants spaced further apart. Spacing had little effect, however, on plant water relations. Independent of cultivar and spacing, stomatal conductance decreased rapidly as stem water potential approached -0.6 to -0.8 MPa. Among cultivars, 'Bluecrop' had the lowest root mass and root:shoot dry weight ratio at either spacing, while 'Elliott' had the highest. 'Duke', however, produced the deepest root system, extracting a significant amount of water below 0.6 m when plants were closely spaced. 'Duke' also maintained, on average, higher stem water potentials and greater stomatal conductance than the other cultivars as soil water was depleted.