Post on 25-Apr-2023
ORIGINAL PAPER
The influence of bearing cycles on olive oil productionresponse to irrigation
A. Ben-Gal • U. Yermiyahu • I. Zipori •
E. Presnov • E. Hanoch • A. Dag
Received: 21 June 2010 / Accepted: 22 September 2010
� Springer-Verlag 2010
Abstract Water requirements for olive oil production and
the effects of deficit irrigation were determined while
considering the relative fruit loads on trees occurring as a
result of biennial bearing cycles. Two Israeli olive (Olea
europaea) varieties (Barnea and Souri) were evaluated for
growth and yield parameters in a 4-year field study where
five relative irrigation rates were applied. Increasing irri-
gation increased stem water potential, vegetative growth,
and olive fruit yield with the increases tapering off at
application rates reaching 75–100% of potential crop
evapotranspiration. Tree water status, growth, and fruit
characteristic parameters were highly affected by both fruit
load and by irrigation level. Oil yield increases as a func-
tion of increased irrigation were initiated for each cultivar
only following an ‘off’ season when the treatments lead to
higher vegetative growth. The increased oil yields as a
function of increased irrigation were primarily explained
by higher tree-scale capacity for carrying fruit, especially
as irrigation alleviated measureable water stress. For the
Barnea cultivar in ‘on’ years, a secondary effect due to
increased oil per fruit as irrigation increased was evident,
particularly at the higher application rates.
Introduction
Olive oil production has historical importance throughout
the Mediterranean where there is evidence of human
cultivation and consumption from as far back as
5,000–6,000 years ago (Vossen 2007). Traditionally, olives
are not irrigated, but recently water application has been
recognized as constructive in order to (a) increase yields of
olives in regions with traditional rain-fed olive production
(Moriana et al. 2003), (b) allow high-density olive orchards
and (c) expand olive production into regions where there is
not enough rainfall to otherwise support the crop (Connor
2005). Under conditions like those in Israel, where growing
season rainfall is insufficient, irrigation has been found to
promote increased olive fruit and oil yields by as much as
fourfold (Grattan et al. 2006; Lavee et al. 1990; Moriana
et al. 2003; Samish and Speigel 1961; Spiegel 1955). This
impressive yield response to water application can be due
to a number of factors. First is that irrigation allows
avoidance of conditions of stress that would otherwise
cause reduced olive oil accumulation in fruits (Fernandez
and Moreno 1999). A second, probably more important,
reason that irrigation increases yields is an augmented
capacity for quantity of fruit per tree (d’Andria and Morelli
2002; d’Andria et al. 2004; Goldhamer et al. 1994; Grattan
et al. 2006; Gucci et al. 2007; Patumi et al. 1999, 2002).
For other than severely stressed trees, oil content on per
fruit basis is not usually found to be affected by water
application (d’Andria et al. 2004; Grattan et al. 2006;
Lavee et al. 2007; Moriana et al. 2003). In fact, oil per-
centage is commonly found to decrease as a function of
Communicated by E. Fereres.
A. Ben-Gal (&) � U. Yermiyahu � E. Presnov
Soil, Water and Environmental Sciences,
Agricultural Research Organization, Gilat Research Center,
85280 Mobile Post Negev II, Israel
e-mail: bengal@volcani.agri.gov.il
I. Zipori � A. Dag
Plant Sciences, Agricultural Research Organization,
Gilat Research Center, 85280 Mobile Post Negev II, Israel
E. Hanoch
The Extension Service, Ministry of Agriculture
and Rural Development, Bet-Dagan, Israel
123
Irrig Sci
DOI 10.1007/s00271-010-0237-1
increased amounts of applied water (Lavee et al. 1990;
Ramos and Santos 2010). Additionally, increased yields
may come at a price in terms of oil quality. Irrigation has
been found to decrease polyphenol content (Ben-Gal et al.
2008; Criado et al. 2007; Dag et al. 2008; Gomez-Rico
et al. 2006; Patumi et al. 1999) and sometimes increase free
fatty acids in oil (Dag et al. 2008).
Olives strongly follow a biennial cycle of growth and
production. Since flowering takes place on 1-year-old
wood and stem biomass growth becomes negligible when
fruit load is high, trees undergo alternated years of vege-
tative and reproductive growth. High yields are produced in
the ‘on’ years followed by ‘off’ years of low (sometimes
zero, often not commercial) yields. Although biennial
bearing is basically genetically determined, the degree to
which it occurs is greatly affected by environmental con-
ditions, especially the weather and by cultivation practices.
Alternate fruit bearing occurs under both extensive and
intensive growing conditions (Lavee 2006). Three principal
regulatory mechanisms that seem to interact strongly, thus
influencing or even inducing alternate bearing are as fol-
lows: hormonal control, nutritional (carbon and mineral
balance) control (Lavee 2006), and flowering site limitation
(Dag et al. 2010).
The objectives of this work were to evaluate water
requirements for olives in a modern Israeli orchard and to
determine effects of deficit irrigation on growth and pro-
duction while considering the relative fruit loads on trees
occurring as a result of biennial bearing cycles.
Materials and methods
Experimental site
The research was conducted in a two-hectare section of a
4-year-old (at onset of treatments) commercial olive
orchard with general upkeep and horticultural practices in
accordance with accepted local commercial practice. The
orchard was located (31�750N, 34�850E) adjacent to Kfar
Menachem and Revadim in the foothills of the Judean Hills
in Israel. The soil of the orchard was a clay vertisol
(sand 20%, clay 65%) with *20% gravel to stone-sized
rock fraction. The climate at the site is Mediterranean,
with highly variable seasonal rainfall averaging around
450 mm year-1 limited to the winter months November–
March. Summers are typically warm and dry with average
daily high temperatures in July and August of 30–35�C and
daytime relative humidity often dropping below 40%.
Winter rainfall and seasonal reference evapotranspiration
(ET0) for the 4 years of this study are found in Table 1.
The orchard section included both a local traditional cul-
tivar, ‘Souri’, and a newly bred local cultivar, ‘Barnea’,
interplanted such that between every four rows of Barnea
there were two rows of Souri. Orchard design and spacing
was to accommodate mechanized harvesting by trunk
shakers. Trees were planted every 3.75 m (Souri) and
4.25 m (Barnea) in rows spaced 7 m apart. The orchard
was drip-irrigated (UniRam 20 mm, 2.3 l h-1, emitter
every 0.5 m; Netafim, Hatzerim, Israel). The irrigation
application for each treatment was determined as a fraction
of the daylight-hour reference evapotranspiration (ET0)
calculated using Penman–Monteith equation (Monteith
1965). Meteorological data were collected from a station
located adjacent to the orchard.
Irrigation water application treatments
Five irrigation levels (30, 50, 75, 100, and 125%) were
given. Actual daily irrigation (I) was computed by:
I ¼ ETp� IrrLev
100; ETp ¼ ET0 � fc ð1Þ
where ETp is potential evapotranspiration, IrrLev is the
level of irrigation for the different treatments (%), and fc is
a cover factor estimated by midday shaded area. The IrrLev
fraction is equivalent to a crop factor (Kc) as found in FAO
crop water consumption methods (Allen et al. 1998). The
cover factor, fc, was estimated as 40% in 2006 and 50%
from 2007 to 2009. Frequency of irrigation events was
once every 3 days early and late in the season and once
every 2 days midseason (approximately June–September).
Statistical design was a randomized split-block with five
replicates per treatment. Each of the 25 experimental units
consisted of six adjacent tree rows (4 Barnea and 2 Souri)
with at least four olive trees per row. Two central trees of
each variety were monitored while those surrounding them
served as border-guard trees. The orchard was irrigated
with effluent that, originating as municipal wastewater in
the city of Jerusalem, underwent secondary, activated
sludge treatment and was stored in a nearby reservoir.
Nitrogen and potassium fertilizer was given with irrigation
water as recommended by the local extension service
equally to all treatments according to area-based calcula-
tions including consideration of nutrients originating in the
recycled wastewater. Seasonally, 200 kg nitrogen and
205 kg potassium were applied per hectare. The effluent
was low in salts and had no other characteristic expected to
influence plant performance.
Variable water application began in the spring of 2006
and continued during the four irrigation seasons (approxi-
mately April–November, depending on rainfall). The
beginning and end of each irrigation season (Table 1) were
dictated by the last and first significant rainfall events each
year. These dates, amount of winter rainfall, total accu-
mulated ET0 during the irrigation season, and the quantity
Irrig Sci
123
of irrigation given to the 100% return of ETp are provided
in Table 1 for each of the four experimental years. Daily
ET0 and rainfall for the four experimental seasons are
given in Fig. 1. Actual seasonal irrigation quantities for
each treatment level are shown in Fig. 2. Differential irri-
gation treatments ranged from 176 to 209 mm (25%
treatment) to 580 mm in the first year and between 730 and
820 mm for the highest (125%) treatment in the subsequent
years.
Alternate bearing
During the spring prior to the initiation of the experiment in
2006, the Souri cultivar flowered plentifully, while the
flowering of the Barnea trees was relatively meager. The
orchard’s two cultivars being in opposite biennial bearing
cycles continued throughout the reported experimental
years. In 2006 and 2008 Souri was ‘on’, with a relatively
high fruit load, and Barnea ‘off’, while in 2007 and 2009
Barnea was ‘on’ and Souri ‘off’. In the 2009 season, the
Souri trees were in a severe ‘off’ year, and no fruit was
harvested.
Measurements
Plant water status was assessed by midday stem water
potential using a Scholander-type pressure chamber
(MRC, Israel) according to Shackel et al. (1997), three
times a year, in May, July, and September. Vegetative
growth rate was measured by annual increased trunk
circumference at a marked point 40 cm above the ground
on each tree. Yield was determined for each monitored
tree, harvested at the appropriate ripeness level (50%
black fruit). Individual fruit weight was determined
from a sample of 100 fruits. Fruit number per tree was
calculated by dividing total fruit yield by average single
fruit weight. Oil percentage was measured by chemical
extraction with Soxhlet. Cold-pressed oil was obtained
with an ‘Abencor’ system (MC2 Ingenieria y Sistemas,
Spain).
Statistical analysis
Data were analyzed using the JMP 5.0 software (SAS
Institute, Cary, NC) and the curve-fitting and analysis tools
of SigmaPlot 10.0 (Systat Software, San Jose, CA). Rela-
tionships between irrigation levels and the measured
parameters were determined using regression analysis. All
statistical analyses were conducted at P B 0.05 unless
otherwise indicated.
Table 1 Seasonal reference climate and irrigation data
Year Rain prior (mm) Irrigation dates Seasonal ET0 (mm) Irrigation 100% (mm)
2006 502 aApril 23–Oct 27 1,119 484
2007 529 April 12–Nov 22 1,302 663
2008 419 March 27–Oct 26 1,292 612
2009 379 April 5–Oct 29 1,124 578
ET0 is reference evapotranspiration according to a modified Penmann Monteith equationa Differential irrigation treatments began May 28, 2006. From April 1–May 27 2006, 85 mm was applied to all treatments
ET
0 (m
m)
2
4
6
8
10
Jan
2006
Jul 2
006
Jan
2007
Jul 2
007
Jan
2008
Jul 2
008
Jan
2009
Jul 2
009
Jan
2010
Rai
n (m
m)
0
40
80
Fig. 1 Daily reference evapotranspiration (ET0) and rainfall during
the experiment
Irrigation treatment (% return ETp)
0 25 50 75 100 125S
easo
nal i
rrig
atio
n (m
m)
0
200
400
600
800
1000
2006200720082009
year
Fig. 2 Actual seasonal irrigation application for target irrigation
levels during the four experimental seasons. ETp is potential
evapotranspiration (reference ET X canopy cover factor)
Irrig Sci
123
Results
Tree water status
Midday stem water potential decreased with time over the
irrigation season as seen for the 2007 season in Fig. 3.
Well-watered trees had midday stem water potential of
approximately -1 MPa in May, -2 MPa in July, and -2.5
(Souri) to -3 MPa (Barnea) in September. Treatment-
related differences in stem water potential developed over
time (Fig. 3; Table 2). The Barnea trees, in an ‘on’ year
with higher fruit load, had consistently lower stem water
potential compared to the Souri trees that were in an ‘off’
year in 2007.
In each of the years, strong correlation of midday stem
water potential to irrigation level was found in September
measurements (Fig. 4; Table 3). In each year and for each
cultivar, extremely low values of stem water potential
ranging from -4 to -5 MPa were measured in the 30%
treatment. For both cultivars in 2006 and 2007 and for
Souri in 2008, stem water potential increased with
increased water application rate up to 100% return. For
Barnea in 2008 and both cultivars in 2009, stem water
potential was not differentiated for treatments of 50%
return and greater. The cultivar in its ‘off’ year consistently
had higher midday stem water potential in comparison with
that in its ‘on’ year as evidenced by higher absolute values
of September stem water potential across all the irrigation
treatments for the Barnea cultivar in 2006 and 2008 and for
the Souri cultivar in 2007 and 2009 (Fig. 4).
Growth
Trunk circumference was measured in March each year.
Initial measures of trunk circumference indicated high
uniformity in the orchard. Average circumference in March
2006 was 44.5 ± 3.6 cm and 44.6 ± 3.7 cm for Barnea
and Souri trees, respectively, with no differences between
treatment groups. Substantially higher measurements of
trunk growth were found in trees in ‘off’ years compared to
those in ‘on’ years (Fig. 5). Trunk expansion rates
increased with increased irrigation in ‘off’ years until
treatment levels 75–100%. In the first 2 years of the
experiment, the cultivars in ‘on’ years had relatively low
growth rates that were related linearly to water application
Irrigation treatment (% return of ETp)
0 25 50 75 100 125
Mid
day
stem
wat
er p
oten
tial (
MP
a)
-5
-4
-3
-2
-1
0
Souri May 17Barnea May 17 Souri July 02 Barnea July 02 Souri Sept 17Barnea Sept 17
Fig. 3 Stem water potential as a function of irrigation rate at three
dates during the 2007 irrigation season. Symbols are average of 10
replicate trees and lines are best-fit linear or 3-parameter exponential
rise to maximum curves. Regression equations and statistics are found
in Table 2
Table 2 Regression equations
and statistics for Fig. 2Cultivar Date Equation (Y = …) R2 P
Souri May 17 -1 ? 0.0019X 0.70 0.08
Barnea May 17 -1.4 ? 0.0032X 0.94 0.006
Souri July 2 -2.3 ? 0.84 9 (1 - exp(-0.013X)) 0.90 0.1
Barnea July 2 -3.1 ? 1.87 9 (1 - exp(-0.008X)) 0.96 0.04
Souri Sep 17 -13.4 ? 11.2 9 (1 - exp(-0.062X)) 0.98 0.02
Barnea Sep 17 -13.1 ? 10.4 9 (1 - exp(-0.055X)) 0.99 0.005
-5
-4
-3
-225 Sep 2008
Irrigation treatment (% return of ETp)
0 25 50 75 100 125 25 50 75 100 125
15 Sep 2009
Mid
day
stem
wat
er p
oten
tial (
MP
a)
-5
-4
-3
-2
-1
BarneaSouri
7002peS716002peS71
Fig. 4 Olive tree stem water potential measured in September of
each year. Heavy fruit loads (‘on’ years) were experienced in 2006
and 2008 in Souri trees and in 2007 and 2009 in Barnea. Symbols are
averages of 10 replicate trees. Lines are best-fit 3-parameter
exponential rise to maximum curves. Regression equations and
statistics are found in Table 3
Irrig Sci
123
rates throughout the range of treatments. In the third and
fourth years, the trunk growth of the cultivars in ‘on’ years
was not affected by irrigation rate (Fig. 5; Table 3).
Yields
Fruit yield
Fruit yield (kg/tree) increased slightly as a function of
increased irrigation for both varieties in 2006 and for Souri
in 2007 (Fig. 6; Table 3). Yield increased substantially as
irrigation increased to 100% treatment for Barnea in 2007,
but no significant difference was found between yields of
the 100 and 125% treatments. In 2008, fruit yield of both
varieties increased with increased irrigation rate up to the
100% treatment. In 2009, the Souri trees had essentially no
fruit and were not harvested. Barnea trees in 2009 strongly
responded to irrigation with the 50% treatment producing
double and the 75–125% levels nearly tripling the fruit
yield found for the 30% treatment. Throughout the four
experimental years, the maximum yields for trees in their
‘on’ year were measured in the 100% treatment.
Fruit number
Souri trees averaged only 2,000 fruits per tree in ‘off’ years
and some 12,500 fruits per tree in ‘on’ years. Barnea trees
had substantially greater numbers of fruit with an average
Table 3 Regression equations and statistics for Figs. 3, 4, 5, 6, 7, 8, and 9
Figure Cultivar Year Equation (Y = …) R2 P
3 Barnea 2006 15.7 ? 13.1(1 - exp(-0.074X)) 0.98 0.01
Souri 2006 9.6 ? 6.9(1 - exp(-0.041X)) 0.99 0.01
Barnea 2007 13.1 ? 10.4(1 - exp(-0.055X)) 0.99 0.005
Souri 2007 13.4 ? 11.2(1 - exp(-0.062X) 0.97 0.02
Barnea 2008 167 ? 164.2(1 - exp(-0.15X)) 0.99 0.001
Souri 2008 14.7 ? 11.5(1 - exp(-0.065X)) 0.99 0.003
Barnea 2009 -4482 ? 4479(1 - exp(-0.26X)) 0.98 0.003
Souri 2009 -108.9 ? 106.5(1 - exp(-0.14X)) 0.98 0.002
4 Barnea 2006-2007 -4.7 ? 15.5(1 - exp(0.045X)) 0.99 0.008
Souri 2006–2007 2.3 ? 0.04X 0.87 0.02
Barnea 2007–2008 3.5 ? 0.2X 0.24 0.01
Souri 2007–2008 -79.6 ? 88.5(1 - exp(0.10X)) 0.98 0.02
Barnea 2008–2009 -9.6 ? 14.1(1 - exp(0.06X)) 0.83 0.1
Souri 2009–2010 -11.1(1 - exp(0.04X)) 0.78 0.08
5 Barnea 2007 -36 ? 144.7(1 - exp(0.033X) 0.96 0.04
Souri 2007 7.1 ? 22.1(1 - exp(0.010X) 0.93 0.01
Barnea 2008 11.2 ? 50.6(1 - exp(0.012X)) 0.89 0.1
Souri 2008 -20.9 ? 76.7(1 - exp(0.040X)) 0.95 0.05
Barnea 2009 -127 ? 220.1(1 - exp(0.048X)) 0.96 0.04
6 Souri 2006 39011-20342 9 exp(-0.024X) 0.89 0.1
Barnea 2008 -22754 ? 41291 9 exp(-0.05X)) 0.93 0.07
Barnea 2009 -13071 ? 1322X - 7.7X2 0.98 0.02
7 Barnea 2006 14.2 9 exp(2.51/(X-25.5)) 0.98 0.02
Souri 2006 26.3 - 0.069X 0.96 0.003
Souri 2007 147.5 9 exp(11.6/(X - 11.1)) 0.99 0.002
Barnea 2008 18.4 9 exp(5.9/(X - 9.1)) 0.97 0.03
8 Barnea 2007 1.0 ? 0.82 9 exp(-0.61X) 0.99 0.02
Souri 2007 -0.91 ? 1.5(1 - exp(0.056X)) 0.99 0.01
Souri 2008 0.71 ? 0.91 9 exp(-0.91X) 0.98 0.02
Barnea 2009 0.29 ? 0.026 9 exp(0.018X) 0.97 0.03
9 Barnea 2007 0.57 ? 18.2(1 - exp(0.031X)) 0.99 0.05
Souri 2008 -12.8 ? 726.5(1 - exp(0.053X)) 0.97 0.03
Barnea 2009 -15.4 ? 32.5(1-exp(0.036X)) 0.96 0.04
Irrig Sci
123
of 9,500 and 34,000 fruits per tree in ‘off’ and ‘on’ years,
respectively. Starting in the second year for Barnea and
third year for Souri, the number of fruit per tree increased
with increasing irrigation rate up to the 75% treatment
level (Fig. 7; Table 3). In 2009, the amount of fruits in the
highest (125%) irrigation level was markedly reduced
compared to the 75 and 100% treatments as seen in the
statistically significant quadratic curve in Fig. 6-2009 and
defined in Table 3 (compared to the non-significant rise-to-
maximum regression curve). Maximum fruit per tree
reached over 20,000 for the 100% treatment in Souri trees
in 2008 and over 43,000 for the 100% treatment in Barnea
trees in 2009.
Oil in fruit
Percent oil in fruit was generally higher in ‘on’ than in ‘off’
years and decreased with increased irrigation level (Fig. 8;
Table 3). Percent oil in olives of both cultivars receiving
30% irrigation was consistently around 25%. In ‘on’ years,
2006-2007
3
6
9
12
2008-2009
Irrigation treatment (% return ETp)
Ann
ual t
runk
gro
wth
(cm
)
0
3
6
9
12 2009-2010
0 25 50 75 100 125 25 50 75 100 125
2007-2008
Barnea Souri
Fig. 5 Annual increases in trunk circumference measured in March
for the four experimental years. Heavy fruit loads (‘on’ years) were
experienced in 2006 and 2008 in Souri trees and in 2007 and 2009 in
Barnea. Symbols are average measured data (n = 10), lines are best-
fit regression of either linear or 2- or 3-parameter exponential rise to
maximum curves. Regression equations and statistics are found in
Table 3
2008
Irrigation treatment (% return ETp)
0 25 50 75 100 1250
30
60
90
2009
25 50 75 100 125
20072006
Fru
it yi
eld
(kg/
tree
)
0
30
60
90
120
BarneaSouri
Fig. 6 Olive fruit yield as a function of irrigation water application
rate. Symbols are average measured values (n = 10) and lines are
best-fit 3-parameter exponential rise to maximum curves. Dotted linesare not significant. Regression equations and statistics are found in
Table 3
Fru
its p
er tr
ee (
#)
0
10000
20000
30000
40000
50000
Barnea Souri
2006 2007
Irrigation treatment (% return ETp)
0
10000
20000
30000
40000
500002008
0 25 50 75 100 125 25 50 75 100 125
2009
Fig. 7 Average number of olive fruits per tree as a function of
irrigation water application rate. Symbols are average measured
values (n = 10), and lines are best-fit regression curves. Dotted linesare not significant. Regression equations and statistics are found in
Table 3
2008
Irrigation treatment (% return ETp)
10
20
302009
0 25 50 75 100 125 25 50 75 100 125
20072006
% o
il in
frui
t
10
20
30 Barnea Souri
Fig. 8 Percent oil by chemical extraction in olive fruit wet weight as
a function of irrigation water application rate. Heavy fruit loads (‘on’
years) were experienced in 2006 and 2008 in Souri trees and in 2007
and 2009 in Barnea. Symbols are average measured values (n = 10),
and lines are best-fit exponential reduction or linear regression curves.
Dotted lines are not significant. Regression equations and statistics are
found in Table 3
Irrig Sci
123
this decreased with irrigation amount fairly linearly to as
low as 18% (for Souri in 2006). In ‘off’ years, increasing
irrigation from 30 to 50% dropped oil percentages to as low
as 15%.
The total oil produced per fruit (calculated by multi-
plying fruit weight by % oil) was influenced inconsistently
by irrigation level (Fig. 9; Table 3). In the initial year of
the experiment, irrigation did not affect oil per fruit. In
2007, oil per fruit increased in Barnea (‘on’ year) and
decreased in Souri (‘off’ year) with the greatest effect
occurring between the 30 and 50% treatment levels. In
2008, both varieties showed trends of decreasing oil per
fruit with increased irrigation (Barnea significant, Souri
not), and in 2009 oil per fruit of Barnea trees again was
augmented by irrigation, but this time with greater relative
increases as irrigation level increased.
Oil yield
Oil yield was calculated as fruit yield multiplied by
chemically extracted oil percentage and is shown in
Fig. 10. Oil yield ranged from zero to almost 10 kg per tree
in ‘off’ years’ and from 6 to 19 kg per tree in ‘on’ years. In
the first year of the experiment, 2006, no effect of irrigation
was found on oil yield. In the second year, 2007, significant
increases in oil yield as a function of irrigation level were
found for Barnea, which was in an ‘on’ year, while no
effect was seen for Souri in an ‘off’ year. In the third year
of the experiment, 2008, significant increases in oil yield
from 30 to 75% return rates were found for Souri in an ‘on’
year, and a non-significant trend of increased oil with
increased water application was indicated for Barnea in an
‘off’ year. In the fourth year, 2009, the Souri trees pro-
duced no fruit and therefore no oil, and Barnea showed
strong increases in oil yield as a function of increased
irrigation until the 100% return treatment level.
Oil extraction efficiency determined as the ratio of % oil
from cold-press (Abencor) to % oil from chemical
extraction (Sohxlet) ranged from near 1 to 0.6. This ratio
was generally higher for Souri compared to Barnea and
consistently decreased for both varieties as a function of
increased irrigation treatment and increased water content
of fruit.
Discussion
In this study, increasing irrigation increased stem water
potential (Figs. 3, 4), vegetative growth (Fig. 5), and olive
fruit yield with the increases tapering off at application
rates above the 75–100% treatments (Fig. 6). Measured
tree status and yield parameters were highly affected by
fruit load. Trees in ‘on’ years generally had lower vege-
tative growth (Fig. 5), lower stem water potential (Fig. 4),
greater fruit yields (Fig. 6) but smaller individual fruits,
had higher oil percentages (Fig. 8), and had higher oil
yields (Fig. 10).
Oil yield increases as a function of increased irrigation
were initiated only in the second year of treatments, and
only for the cultivar Barnea for which the first year was an
‘off’ season when the treatments lead to higher vegetative
growth. Yields of fruit and oil for Souri trees were sig-
nificantly improved by irrigation just in the third year of the
experiment, which was this variety’s only ‘on’ year
Oil
per
frui
t (g)
0.0
0.3
0.6
0.9
1.2
Barnea Souri
2006 2007
Irrigation treatment (% return ETp)
0.0
0.3
0.6
0.9
1.2 2008
0 25 50 75 100 125 25 50 75 100 125
2009
Fig. 9 Average olive oil content of individual fruits as a function of
irrigation water application rate. Heavy fruit loads (‘‘on’’ years) were
experienced in 2006 and 2008 in Souri trees and in 2007 and 2009 in
Barnea. Symbols are average measured values (n = 10), and lines are
best-fit regression curves. Dotted lines are not significant. Regression
equations and statistics are found in Table 3
2009
25 50 75 100 125
2008
Irrigation treatment (% return ETp)
0 25 50 75 100 1250
5
10
15
20072006
Oil
yiel
d (k
g/tr
ee)
0
5
10
15
20
BarneaSouri
Fig. 10 Olive oil yield as a function of irrigation water application
rate. Symbols are average measured values (n = 10), and lines are
best-fit 3-parameter exponential rise to maximum or linear regression
curves. Dotted lines are not significant. Regression equations and
statistics are found in Table 3
Irrig Sci
123
subsequent to an ‘off’ year under irrigation treatments. We
suspect that fruit yield would continue to show an accu-
mulated positive response to irrigation in both ‘on’ and
‘off’ years, assuming continuation of treatment levels and
development of trees with greater fruit-bearing capacity.
The effects of deficit irrigation regimes on tree water
status developed each season gradually as moisture stored
in the soil from winter rains was depleted and climate
demand increased to maximum levels. The dynamic of
little to no stress in the first months of annual irrigation,
moderate stress in July and maximum stress in September,
measured as decreasing stem water potential in trees
receiving deficit irrigation applications, closely followed
those found in Tunisia (Guerfel et al. 2007) and are gen-
erally comparable with data from drought-stressed or def-
icit-irrigated orchards in Portugal (Ramos and Santos
2010), Italy (d’Andria et al. 2009; Giorio et al. 1999), and
Spain (Moriana et al. 2003, 2007; Perez-Lopez et al. 2007).
This pattern of dynamic decreasing of stem water potential
throughout the summer was found in additional studies to
be accompanied by reduced stomatal conductance (Ben-
Gal et al. 2009; Guerfel et al. 2007; Moriana et al. 2007)
and diminished photosynthetic capacity (Dıaz-Espejo et al.
2006; Guerfel et al. 2007). Of course, in many of the tra-
ditional Mediterranean olive-growing regions, there often
is significant rainfall occurring later into the spring, and
midsummer climate conditions at these locations will often
be less demanding regarding ET requirements than those at
our site in Israel. In such cases, tree water status would be
more slowly affected and reach less severe levels at
equivalent relative irrigation return rates. In all variations
of Mediterranean climates, little if any water stress would
be expected during flowering and fruit set stages, and
therefore management strategies for drought avoidance
during the spring are likely not effective or necessary. This
study supports others that indicate late season water stress,
following pit hardening and accompanying oil accumula-
tion in olive fruits, as particularly harmful to oil production
(Inglese et al. 1996; Moriana et al. 2007; Tognetti et al.
2006).
The results suggest that mechanisms for drought
avoidance in olives, involving stomatal closure, water
conservation, and maintenance of tree water potential and
turgor, are fruit load specific. Trees with a large number of
fruits will keep stomates open, continue transpiration, dry
their soil, and enter higher levels of water stress, compared
to trees with low fruit loads. This apparent favoring of
photosynthesis and supply of assimilates to the growing
fruits when fruit load is high, at the expense of water
budget and entering into water stress, has been well doc-
umented for apple (Fuji and Kennedy 1985; Giuliani et al.
1997; Gucci et al. 1994; Palmer 1992; Wibbe et al. 1993;
Wunsche and Palmer 1997; Wunsche et al. 2000) and
indicated for other deciduous fruit trees (DeJong 1986;
Marsal et al. 2005; Naor et al. 1997; Naor et al. 2008). This
theory, strongly supported by the current results, has been
suggested for olives (Moriana et al. 2002, 2003) but was
not found in a number of studies on ‘Leccino’ olives in
Italy. In separate 2-year studies, Proietti (2000) found no
influence of the presence or absence of fruit on leaf pho-
tosynthetic activity, and Gucci et al. (2007) reported no
effect of crop load on leaf water potential.
Deficit irrigation led to decreased biomass growth in this
study during all ‘off’ years and in the first years of the
experiment in ‘on’ years as well. While there is little data
concerning biomass or canopy growth reported in the lit-
erature on deficit irrigation of olives, it is generally
understood that shoot growth and canopy size in olives
increase as a function of sustained water supply (Connor
2005; Gomez-del-Campo et al. 2008; Tognetti et al. 2006).
Similar to us, d’Andria et al. (2004) reported significant
increased accumulated trunk growth as a function of
increased irrigation after 4 years of treatments, but they did
not supply annual data. Slightly different results compared
to ours were found by Perez-Lopez et al. (2007) who
reported decreased shoot growth rates for deficit regimes in
the second and third years of their study, but not in the first
year. Some enlightenment might be found in the Fernandez
and Cuevas (2010) review of irrigation scheduling using
stem diameter variations where they showed that trunk
growth rates were highly dependent on fruit load. Olive
trees in ‘on’ years grew very fast early in the spring and
until some 4 weeks after full bloom, but thereafter their
growth rate became very low to negligible. Conversely,
trees with light loads grew steadily throughout the season.
The stronger effect of water stress on growth of the trees in
‘off’ years in our current study could therefore be expected.
More intriguing is the fact that ‘on’ year trunk growth was
linearly increased by increased water application in the first
2 years of the experiment (for a single season for each
variety), but this did not continue in the next cycle of
alternative bearing (Fig. 4).
The literature suggests that fruit and oil yield response
to irrigation is highly cultivar specific (Lavee et al. 2007).
Ramos and Santos (2010) did not report differences in fruit
or oil yield between fully and deficit-irrigated mature
‘‘Cordovil’’ olives in their 2-year study. Moriana et al.
(2007) did find greater fruit and oil yields in well-irrigated
compared to deficit-irrigated ‘‘Cornicabra’’ trees in their
initial year when the trees were ‘on’ but no influence of
irrigation regime on yields in the subsequent ‘off’ year.
Lavee et al. (2007) found that increased yield due to
increased irrigation in the cultivar ‘‘Muhasan’’ was solely
due to increased fruit number. Oil per fruit was no greater
in well-irrigated compared to deficit-irrigated treatments.
Additionally, oil extraction in the well-irrigated fruits was
Irrig Sci
123
less efficient than in the less-irrigated fruits in their study.
Results of d’Andria et al.’s (2009) 4-year study were
similar to ours as total accumulated fruit and oil yield both
increased linearly as water application increased within
their four irrigation regime treatment levels from 0 to 100%
ETc. Patumi et al. (1999, 2002) and Tognetti et al. (2006)
also reported positive correlations between irrigation level
and fruit and oil yield. Regarding ‘on’ and ‘off’ relation-
ships between fruit and oil yield and irrigation rate, Ramos
and Santos (2010) reported irrigation treatments leading to
particularly high stress levels decreased relative yields
more in the ‘off’ than in the ‘on’ year of their 2-year study.
Perez-Lopez et al. (2007) showed a linear relationship
between canopy volume and yield in the 2 ‘on’ years and
no such relationship in the single ‘off’ year of their 3-year
study.
Studies of olives are expected to benefit from single
tree-level scrutiny, allowing sensitivity analysis of results
to variables expected to be naturally non-uniform as well as
affected by irrigation management. Therefore, analysis of
oil yields of individual trees was conducted in this study to
help determine how much of the yield effect was due to
trees with more fruits and how much was due to more oil
production per fruit (Figs. 11, 12). Tree-scale oil yield was
consistently correlated with fruit load (number of fruits per
tree) as seen in Figs. 11 and 12 for both Barnea and Souri,
and sometimes correlated with oil per fruit for Barnea only.
Fruit load was clearly both a function of natural variations
and 4 years of irrigation regime. Whole tree oil yield was
highly correlated with number of fruits on a tree but, as
seen in the lower treatment levels sitting below the
regression line in Fig. 11h and the higher treatments sitting
above it, it is not the only relevant factor. At least for
Barnea in ‘on’ years, it is evident that oil per fruit increased
by increased irrigation also plays a role (Fig. 11c, g). This
is additionally supported by the ‘‘separation’’ of the treat-
ments across the fruit load-oil yield regression line in
Fig. 10d and h. No such per fruit increases in oil were
evident for Souri where oil per fruit was negatively cor-
related with tree oil yield (Fig. 12e) and where the treat-
ments spread evenly along the regression line in Fig. 12f.
The results therefore suggest a dual mechanism for
increased tree-level oil yields as a function of increased
irrigation for the Barnea cultivar. The major effect, seen
distinguishing the most severe deficit regime from all the
other water application rates, was due to trees with higher
fruit-carrying capacity. Trees receiving greater amounts of
water in ‘off’ seasons had greater vegetative growth that
supported a larger number of fruits the following year. The
second, minor, effect was increased amount of oil per fruit
found as a function of increased irrigation rate, especially
at the highest treatment levels. Greater irrigation caused
larger fruits with more oil per fruit. This is in spite of the
fact that % oil in fruit was reduced as a function of
increased irrigation (Fig. 8). Similar results were presented
by d’Andria et al. (2009) who found linear increases of
fruit number per tree, fruit yield and oil yield (averages for
4 years) for both ‘‘Leccino’’ and ‘‘Frantoio’’ cultivars. But
fruit number could not explain all of the yield response in
that study as fruit yield decreased 41%, oil yield 37%, and
fruit number only 23% when irrigation level decreased
from 100% ETc. to 0% ETc.
The oil quality parameters from this study, which will be
presented in detail in a separate publication, reconfirm
previous findings that increasing irrigation leads to fruits
with greater water content (lower oil percentage) as well as
to relative decreases in total polyphenol content and
sometimes to increased free fatty acids (Dag et al. 2008).
They therefore support studies that have suggested conflicts
between olive oil yield and quality relating to water
application (Lavee et al. 2007; D’Andria et al. 2009;
Dabbou et al. 2010; Moriana et al. 2007) and that have
indicated that deficit irrigation regimes are likely to opti-
mize oil production. Water stress management for target oil
quality is becoming more popular and seems to become
a likely aspect of orchard management—especially in
g
Oil per fruit (g)
0
10
20
30
e
0
10
20
30
b
Y=-0.08+7.34X
R2=0.90, P<0.0001
c
Oil
yiel
d (k
g/tr
ee)
0
10
20
30
Y=1.66+32.6X
R2=0.55, P<0.0001
d
Y=7.20+0.0003X
R2=0.19, P=0.0025
h
Fruit load (# fruits/tree)
0.0 0.3 0.6 0.9 1.2 0 20000 40000 60000 80000
Y=4.28+0.0003X
R2=0.60, P<0.0001
f
Y=3.24+0.0004X
R2=0.88, P<0.0001
2007
a
0
10
20
30 305075100125
2006
2008
2009
Fig. 11 Correlation between tree-scale oil yield and oil per fruit (left)and fruit per tree (right) for individual Barnea trees. Markers are
measured data, and the lines are best-fit linear regression for each
entire data set for each season. Dotted lines are not significant
Irrig Sci
123
high-density orchards and orchards where relatively high
irrigation regimes are dictated (saline and wastewater
irrigation). It is likely that regulated, temporal, deficit
irrigation during certain olive growth stages will eventually
target desired water stress levels in attempts to secure
quality levels without harming yields. Additionally, the
fact that efficiency of cold-pressed techniques for oil
extraction decreased as irrigation level/water content of
fruit increased supports earlier work, suggesting that irri-
gation regimes should be properly matched to (and/or with)
extraction methods (Giovacchino et al. 1994; Dag et al.
2008).
Many of the parameters measured in this study are sus-
pected to be cultivar and environment specific (Fernandez
and Moreno 1999; Lavee et al. 2007). The unique case
where two varieties were in opposite alternate bearing
cycles allowed interpretation of the relative importance of
water availability across cultivars while considering irri-
gation and bearing levels. The absolute values of parame-
ters responding to irrigation/stress level were not cultivar
related, were very highly correlated to fruit load, and only
secondarily were a function of irrigation level.
The results suggest a number of likely methods to
improve irrigation management including irrigation
regimes that are cultivar specific and irrigation systems that
cater to each variety individually. Stress levels and water
requirements are highly dependent on fruit load and best
irrigation management must account for biannual bearing
effects. More work is necessary in order to confirm these
data over an even longer term, to determine optimum water
stress scheduling (stress levels and timing) for best yield–
quality combinations, and to further develop methods for
monitoring and maintaining water stress levels.
Acknowledgments The research was supported by The Chief Sci-
entist of Israel’s Ministry of Agriculture and Rural Development
(project #303-0300), the Netafim Company, and The USDA-ARS via
The Middle East Regional Irrigation Management Information Sys-
tem (MERIMIS). Thanks to TZ’’ABAR K’’AMA for providing the
orchard and orchard management support and to Professor Shimon
Lavee for consultation and advice.
References
Allen RG, Pereira LS, Raes D, Smith M (1998) Crop evapotranspi-
ration: guidelines for computing crop water requirements. In:
FAO irrigation and drainage paper no. 56. FAO, Rome
Ben-Gal A, Dag A, Yermiyahu U, Zipori Y, Presnov E, Faingold I,
Kerem Z (2008) Evaluation of irrigation in a converted, rain fed
olive orchard: the transition year. Acta Hortic 792:99–106
Ben-Gal A, Agam N, Alchanatis V, Cohen Y, Zipori I, Presnov E,
Yermiyahu U, Sprintsin M, Dag A (2009) Evaluating water
stress in irrigated olives: correlation of soil water status, tree
water status and thermal imagery. Irrig Sci 27:367–376
Connor DJ (2005) Adaptation of olive (Olea europea L.) to water-
limited environment. Aust J Agric Res 56:1181–1189
Criado M, Romero MP, Moltiva MJ (2007) Effect of the technolog-
ical and agronomical factors on pigment transfer during olive oil
extraction. J Agric Food Chem 55:5681–5688
d’Andria R, Morelli G (2002) Irrigation regime affects yield and oil
quality of olive trees. Acta Hort 586:273–276
d’Andria R, Lavini A, Morelli G, Patumi M, Terenziani S, Calandrelli
D, Fragnito F (2004) Effects of water regimes on five pickling
and double aptitude olive cultivars (Olea europea L.). J Hortic
Sci Biotechnol 79:18–25
d’Andria R, Lavini A, Morelli G, Sebastiani L, Tognetti R (2009)
Physiological and productive responses of Olea europaea L.
cultivars Frantoio and Leccino to a regulated deficit irrigation
regime. Plant Biosyst 143:222–231
Dabbou S, Chehab H, Faten B, Dabbou S, Esposto S, Selvaggini R,
Taticchi A, Servili M, Montedoro GF, Hammami M (2010)
Effect of three irrigation regimes on Arbequina olive oil
produced under Tunisian growing conditions. Agric Water
Manage 97:763–767
Dag A, Ben-Gal A, Yermiyahu U, Basheer L, Yogev N, Kerem Z
(2008) The effect of irrigation level and harvest mechanization
on virgin olive oil quality in a traditional rain-fed ‘‘Souri’’ olive
orchard converted to irrigation. J Sci Food Agric 88:1524–1528
Dag A, Bustan A, Avni A, Zipori I, Lavee S, Riov J (2010) Timing of
fruit removal affects concurrent vegetative growth and subse-
quent return bloom and yield in olive (Olea eropaea L.). Scientia
Hort 123:469–472
DeJong TM (1986) Effects of reproductive and vegetative sink
activity on leaf conductance and water potential of Prunuspersica L. Batsch Scientia Hort 29:131–137
Di Giovacchino L, Solinas M, Miccoli M (1994) Effect of extraction
systems on the quality of virgin olive oil. J Am Oil Chem Soc
71:1189–1194
Dıaz-Espejo A, Walcroft AS, Fernandez JE, Hafidi B, Palomo MJ,
GirOn IF (2006) Modeling photosynthesis in olive leaves under
drought conditions. Tree Physiol 26:1445–1456
a
0
5
10
15
20b
Y=2.54+0.0006X
R2=0.73, P<0.0006
c
Oil
yiel
d (k
g/tr
ee)
0
5
10
15 Y=10.44-5.88X
R2=0.12, P=0.01
e
Oil per fruit (g)
0
5
10
15
Y=17.80-8.26X
R2=0.26, P<0.0001
f
Fruit load (# fruits/tree)
0.0 0.3 0.6 0.9 1.2 0 10000 20000 30000 40000
Y=5.34+0.0004X
R2=0.70, P<0.0001
Y=0.48+0.0009X
R2=0.95, P<0.0001
305075100125
d
2006
2007
2008
Fig. 12 Correlation between tree-scale oil yield and oil per fruit (left)and fruit per tree (right) for individual Souri trees. Markers are
measured data, and the lines are best-fit linear regression for each
entire data set for each season. Dotted lines are not significant
Irrig Sci
123
Fernandez JE, Cuevas MV (2010) Irrigation scheduling from stem
diameter variations: a review. Agric For Meteorol 150:135–151
Fernandez JE, Moreno F (1999) Water use by the olive tree. J Crop
Prod 2:101–162
Fuji JA, Kennedy RA (1985) Seasonal changes in photosynthetic rate
in apple trees. Plant Physiol 78:519–524
Giorio P, Sorrentino G, d’Andria R (1999) Stomatal behaviour, leaf
water status and photosynthetic response in field-grown olive
trees under water deficit. Environ Exp Bot 42:95–104
Giuliani T, Coreli-Grappadeli L, Magnanini E (1997) Effects of crop
load on apple photosynthetic responses and yield. Acta Hort
451:303–311
Goldhamer DA, Dunai J, Ferguson L (1994) Irrigation requirements
of olive trees and responses to sustained deficit irrigation. Acta
Hort 356:172–175
Gomez-del-Campo M, Leal A, Pezuela C (2008) Relationship of stem
water potential and leaf conductance to vegetative growth of
young olive trees in a hedgerow orchard. Aust J Agric Res
59:270–279
Gomez-Rico A, Salvador MD, La Greca M, Fregapane G (2006)
Phenolic and volatile compounds of extra virgin olive oil (Oleaeuropaea L. Cv. Cornicabra) with regards to fruit ripening and
irrigation management. J Agric Food Chem 54:7130–7136
Grattan SR, Berenguer MJ, Connell JH, Polito VS, Vossen PM (2006)
Olive oil production as influenced by different quantities of
applied water. Agric Water Manag 85:133–140
Gucci R, Coreli-Grappadeli L, Tustin S, Ravaglia G (1994) The effect
of defruiting at different stages of fruit development on leaf
photosynthesis of ‘Golden Delicious’ apple. Tree Physiol
15:35–40
Gucci R, Lodolni E, Rapoport HF (2007) Productivity of olive trees
with different water status and crop load. J Hortic Sci Biotechnol
82:648–656
Guerfel M, Baccouri B, Boujnah D, Zarrouk M (2007) Seasonal
changes in water relations and gas exchange in leaves of two
Tunisian olive (Olea europaea L.) cultivars under water deficit.
J Hortic Sci Biotechnol 82:721–726
Inglese P, Barone E, Gullo G (1996) The effect of complimentary
irrigation on fruit growth, ripening pattern and oil characteristics
of olive (Olea europea L.) cv. Gullo. J Hortic Sci 71:257–263
Lavee S (2006) Biennial bearing in olive (Olea europaea L.). Olea
FAO Olive Netw 25:5–13
Lavee S, Nashef M, Wodner M, Harshemesh H (1990) The effect of
complementary irrigation added to old olive trees (Olea euro-paea L.) cv Souri on fruit characteristics, yield and oil
production. Adv Hortic Sci 4:135–138
Lavee S, Hanoch E, Wodner M, Abramowitch H (2007) The effect of
predetermined water deficit on the performance of cv. Muhasan
olives (Olea europea L.) in the eastern coastal plain of Israel.
Scientia Hort 112:156–163
Marsal J, Lopez G, Girona J, Basile B, DeJong TM (2005)
Heterogeneity? in fruit distribution and stem water potential
variations in peach trees under different irrigation conditions.
J Hortic Sci Biotechnol 80:82–86
Monteith JL (1965) Evaporation and environment. Symp Soc Exp
Biol XIX:205–234
Moriana A, Villalobos FJ, Fereres E (2002) Stomatal and photosyn-
thetic responses of olive (Olea europea L.) leaves to water
deficit. Plant Cell Environ 25:395–405
Moriana A, Orgaz F, Pastor M, Fereres E (2003) Yield responses of a
mature olive orchard to water deficit. J Am Soc Hortic Sci
128:425–431
Moriana A, Perez-Lopez D, Gomez-Rico A, Salvador MDD, Olme-
dilla N, Ribas F, Fregapane G (2007) Irrigation scheduling for
traditional, low-density olive orchards: water relations and
influence on oil characteristics. Agric Water Manage
87:171–179
Naor A, Gal Y, Bravdo B (1997) Crop level affects assimilation
rate, stomatal conductance, stem water potential and water
relations of field-grown Sauvignon blanc grapevines. J Exp Bot
48:1675–1680
Naor A, Naschitz S, Peres M, Gal Y (2008) Response of apple fruit
size to tree water status and crop load. Tree Physiol
28:1255–1261
Palmer JW (1992) Effects of varying crop load on photosynthesis, dry
matter production and partitioning of Crispin/M.27 apple trees.
Tree Physiol 11:19–33
Patumi M, d’Andria R, Fontanazza G, Morelli J, Giorgo P, Sorrentino
G (1999) Yield and oil quality on intensively trained trees of
three cultivars of olive (Olea europea L.) under different
irrigation regimes. J Hortic Sci Biotechnol 74:729–737
Patumi M, d’Andria R, Marsilo V, Fontanazza G, Morelli G, Lanza B
(2002) Olive and olive oil quality after intensive monocone olive
growing (Olea europaea l., cv. Kalamata) in different irrigation
regimes. Food Chem 77:27–34
Perez-Lopez D, Ribas F, Moriana A, Olmedilla N, de Juan A (2007)
The effect of irrigation schedules on the water relations and
growth of a young olive (Olea europaea L.) orchard. Agric
Water Manage 89:297–304
Proietti P (2000) Effect of fruiting on leaf gas exchange in olive (OleaEuropaea L.). Photosynthetica 38:397–402
Ramos AF, Santos FL (2010) Yield and olive oil characteristics of a
low-density orchard (cv. Cordovil) subjected to different irriga-
tion regimes. Agric Water Manag 97:363–373
Samish RM, Speigel P (1961) The use of irrigation in growing olives
for oil production. Israel J Agric Res (Ktavim) 11:87–95
Shackel KA, Ahmadi H, Biasis W, Buchner R, Goldhamer D,
Gurusinghe S, Hasey J, Kester D, Krueger B, Lampininen B,
McGourty G, Micke W, Mitcham E, Olson B, Pelletrua K,
Philips H, Ramos D, Schwankl L, Sibbett S, Snyder R,
Southwick S, Stevenson M, Thorpe M, Weinbaum S, Yeager J
(1997) Plant water status as an index of irrigation need in
deciduous fruit trees. HortTechnology 7:23–29
Spiegel P (1955) The water requirement of the olive tree, critical
periods of moisture stress, and the effect of irrigation upon the oil
content of its fruit. Report of the XIVth International Horticul-
tural Congress. Wageningen, Netherlands. pp 1363–1373
Tognetti R, d’Andria R, Lavini A, Morelli G (2006) The effect of
deficit irrigation on crop yield and vegetative development of
Olea europaea L. (cvs. Frantoio and Leccino). Eur J Agron
25:356–364
Vossen P (2007) Olive oil: history, production and characteristics of
the world’s classic oils. HortScience 42:1093–1110
Wibbe ML, Blanke MM, Lenz F (1993) Effect of fruiting on carbon
budgets of apple tree canopies. Trees 8:56–60
Wunsche JN, Palmer JW (1997) Effects of fruiting on seasonal leaf
and whole canopy carbon dioxide exchange of apple. Acta Hort
451:295–301
Wunsche JN, Palmer JW, Greer DH (2000) Effect of crop load on
fruiting and gas exchange characteristics of ‘Braeburn’/M.26
apple trees at full canopy. J Am Soc Hortic Sci 125:93–99
Irrig Sci
123