2. Materials and methods
2.1. Study sites and sample collection
The work was performed in two stages: a preliminary survey of SWR
in six olive orchards in four different locations consisted of different soil
types irrigation-water qualities, olive cultivars and tree ages (Table 1).
This study was followed by a comprehensive study in one of the olive
orchards consisted of different tree's age and a similar soil type. The
persistence of the soil water repellency was determined by WDPT test.
Drop penetration time was measured in the laboratory for 91 undisturbed
soil samples taken along six transects in Revadim grove (RD),
29 samples along two transects in the Karmey Yossef grove (KY), 27
samples along two transects in a Kefar Shmuel freshwater-irrigated
grove (KS1) and 28 samples along two transects in a Kefar Shmuel
rain-fed grove (KS2). 72 samples from six transects in the young
orchard in Revivim (RM1) and 38 samples from three transects in the
mature Revivim plot (RM2).
Following the preliminary survey, which showed that olive trees
tend to confer a certain extent of SWR, a comprehensive study was performed
in Revivim commercial olive grove. The Revivim orchard is
located in the northern part of the Negev desert, Israel. The climate is
arid with annual rainfall of less than 100 mm and the soil is Aeolian
sand having poor SOM content (Table 1). The Revivim orchard is irrigated
with saline water (EC = 3.4 dS/m). Two plots, 100 m apart,
were chosen: one with 5-year-old trees (RM1), and one with 15-yearold
trees (RM2). Samples were also taken from a nearby bare soil area
for reference purposes (RM0).
Undisturbed soil samples were taken along transects between two
adjacent trees parallel to the drip lateral, and transects perpendicular
to these. The sampling points were 40 cm apart. The samples were