Apricot trees

Agricultural Water Management 50 (2001) 211±227

Water balance of apricot trees (Prunus armeniaca
Â
L. cv. Bulida) under drip irrigation
J.M. Abrisquetaa,*, A. Ruizb, J.A. Francoc
a
Â Â
Departamento de Riego y Salinidad, Centro de Edafologõa y Biologõa Aplicada del Segura (CSIC),
P.O. Box 4195, 30080 Cartagena, Murcia, Spain
b
Â Â
Departamento de Ingenierõa Agroforestal, Escuela Politecnica Superior de Orihuela,
Â
Universidad Miguel Hernandez, Elche, Alicante, Spain
c
Â Â
Departamento de Produccion Agraria, ETSIA, Universidad Politecnica de Cartagena,
Alfonso XIII 52, 30204 Cartagena, Murcia, Spain
Accepted 17 November 2000

Abstract

Â
The water balance of drip irrigated apricot trees (Prunus armeniaca L. cv. Bulida grafted onto
``Real®no'' apricot rootstock) was determined during a 30-month-period. Two irrigation regimes
based on the reduction coef®cients of Class A pan evaporation (1 and 0.5) were used to determine
the water consumed. The water balance parameters for these treatments are shown and discussed in
detail. Overall, the trees receiving less water showed 35% less evapotranspiration. Crop coef®cients
calculated on the basis of the water balance over a 30-month-period led to a saving of almost 14%
water, since the coef®cients were slightly below those used in other apricot orchards in the same
area. # 2001 Elsevier Science B.V. All rights reserved.

Keywords: Water balance; Apricot tree; Drip irrigation

1. Introduction

During the last decade, world apricot production has hovered around 2.3 millions tons,
with Mediterranean countries being responsible for about half this figure. In 1992 this
figure was 1.2 million tons (about 60% of the world total) (http://www.fao.org/, 1999).
In global terms, apricot is the 13th most cultivated fruit and Turkey is the principal
producer (13.2%) followed by Spain (7.5%), Italy (6.2%) and France (5.8%) (http://
www.fao.org/, 1999).

*
Corresponding author. Tel.: ‡34-968-396200; fax:‡34-968-396213.
E-mail address: jmabrisq@natura.cebas.csic.es (J.M. Abrisqueta).

0378-3774/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 0 8 6 - 5

212 J.M. Abrisqueta et al. / Agricultural Water Management 50 (2001) 211±227

The average quantity of apricots produced by Spain is 172,000 t although occasionally
the figures fall below this: 119,000 t in 1990, 138,700 t in 1995 and 127,800 t in 1997, for
example. Most Spanish production is concentrated in the provinces of Murcia (79,532 t)
and Valencia (40,146 t) with these quantities representing 57.3 and 28.9%, respectively,
of the national total in 1995 (http://www.sederu.es/, 1999).
Murcia (SE Spain) has the largest area of apricots (12,089 ha, 43.3% of the Spanish
total) and a mean production of 101,125 t between 1990 and 1997. Most plantations are
irrigated, approximately 8% by drip-irrigation and the rest by traditional flooding
techniques.(http://www.carm.es/, 1999).
Â
As regards the different cultivars used, Bulida is the most popular (50,000±90,000 t),
followed by Clases, Tempranos and Realfino (http://www.carm.es/, 1999).
Â
Given the economic importance of the variety Bulida in Spain in general and Murcia in
particular, and given water shortage problems in SE Spain, it is important to study
improved water management strategies in order to obtain maximum production and
quality accompanied by the lowest consumption of water (Torrecillas et al., 1997;
Â
Ruiz-Sanchez et al., 2000).
The aim of this experiment was to study the water balance of drip-irrigated Bulida Â
apricot to establish its water consumption during vegetative growth and to calculate the
local crop coefficients in an attempt to save water.

2. Materials and methods

2.1. Experimental site

The experiment was carried out at a farm located 35 km East of the city of Murcia on
the Mediterranean coast of Spain (37852H N; 1825H W; altitude 340 m). The soil is a Xeric
torriorthent with loam texture, showing no variation to a depth of 1 m. The main soil
properties are shown in Table 1.
Texture characterisation was carried out from 40 soil profiles forming a regular
network. Soil samples were taken with an auger at 0.25 m intervals and with a maximum
depth of 1 m. The granulometric composition was determined for each sample (coarse

Table 1
Average soil properties for the top 1 m

Clay (<0.002 mm) (%) 24.90
Silt (0.05±0.002 mm) (%) 42.52
Fine sand (0.2±0.05 mm) (%) 28.87
Coarse sand (2±0.2 mm) (%) 3.70
Texture Loam
EC (1:5) (dS mÀ1) 0.25
CEC (cmol kgÀ1) 9.7
Organic matter (%) 1.07
Total calcium carbonate (% of total soil) 65.00
Active calcium carbonate (% of total soil) 15.75

J.M. Abrisqueta et al. / Agricultural Water Management 50 (2001) 211±227 213

sand, 2±0.2 mm; fine sand, 0.2±0.05 mm; silt, 0.05±0.002 mm and clay, <0.002 mm), as
were the d50 parameter, the mean granulometrics and the mean d50 for each profile, and
the mean values for each depth. (Liu and Evet, 1984).
No vertical variability in the texture could be observed. The horizontal variability was
expressed by taking into account the parameter d50 (which correctly characterises the
granulometric fractions). This parameter did not present any anisotropy, but it did show a
structure with spatial variation that fitted a gaussian variogram model, with a sill of 6.5
(with no nugget effect) and a range of 35 m. On the map of d50 isovalues that was
obtained by kriging, it was possible to detail the zone where the measuring points should
be located (Ruiz, 2000).
A hydraulic characterisation of the soil was made to define the function K(y) at the
bottom of the profile (and to enable drainage to be estimated) as described by Hillel et al.
(1972). The K(y) relationship is given by

K ˆ 1:95 Â 10À4 e0:3682y …R2 ˆ 0:9948ÃÃÃ † (1)

where K is the hydraulic conductivity (mm hÀ1) and y the volumetric water content (%).
The climate of the area is typically Mediterranean, with mild winters and low rainfall,
and hot dry summers.

2.2. Crop management, irrigation treatments and experimental design

The plant material studied was the apricot tree (Prunus armeniaca L. cv. Bulida, Â
grafted onto Realfino apricot rootstock). This cultivar is autochthonous to SE Spain and is
highly considered because of its good adaptation to different cultivation conditions and it
excellent production.
The trees were planted in 1986, spaced 8 m Â 8 m apart. The plot was drip irrigated by
lines of emitters using seven autocompensating emitters per tree set 1 m from each other.
Each had a 4 l hÀ1 flow rate (Fig. 1).
All the trees in this experiment received the same fertiliser dosage, taking into account
data from the literature on apricot tree cultivation under localised irrigation in the
province of Murcia. The rates were adjusted when necessary in accordance with results of
the periodical leaf analyses carried out. Fertigation techniques were used to provide the
following fertilisers during the year (1 h per day in all cases): 170 kg haÀ1 of nitrogenated
solution (32% N), in February and September, 320 kg haÀ1 NO3K, in March±May and
October, 40 kg haÀ1 (NO3)2Ca, and 40 kg haÀ1 (NO3)2Mg, in March and May,
180 kg haÀ1 NO3NH4, in June±August, 199 kg haÀ1 PO4H3, in January, February,
June±August and November, and 7 kg haÀ1 EDDHA-Fe (6% Fe), in March and May.
From July 1995, the trees were subjected to two drip irrigation treatments (T-1 and T-2)
with four replications per treatment distributed in random blocks. The irrigation
treatments were programmed using two reduction percentages of the US Weather Bureau
Class A pan evaporation. The reduction applied were 0 and 50% for T-1 and T-2
treatments, respectively.
The water applied in T-1 was considered sufficient to satisfy fully the needs of the crop
(100% ETc), and to allow good rooting and tree growth.


Fig. 1. Distribution of neutron probe access tubes and emitters in the tree-spacing: (S), emitter and (*), tube.

The total amount of irrigation water (TIW) applied in treatment T-1 was calculated
from
Kp Kc Kl
TIW ˆ Â Epan (2)
E a Eu
where Kp is the pan coef®cient (0.75; Doorenbos and Pruitt, 1977), Kc the crop
coef®cient, Kl the shade coef®cient (0.97; Freeman and Garzoli, (cited by Vermeiren and
Jobling, 1986), taking into account that the estimated mean shaded surface provided by
the tree canopies was 87% of the total surface of the orchard), Ea the ef®ciency of the
irrigation method (0.95; according to Guidelines for Pressure Irrigation, 1983), Eu the
coef®cient of uniformity of emitters (0.9). The Kc values used in the areas where the
experimental farm is sited are 0.5 in January, February, July±December; 0.75 in March;
0.8 in April; 0.9 in May and 0.6 in June.
Applying the reduction percentages mentioned above to Eq. (2) gives the following
total amounts of irrigation water in each treatment:
TIW…T-1† ˆ 0:76Epan …for treatment T-1† (3)
TIW…T-2† ˆ 0:38Epan …for treatment T-2† (4)

The amount of irrigation water to be applied during a particular week was calculated
from the daily evaporation values measured in the Class A pan during the preceding
Â
week. (Fereres et al., 1982; Leon et al., 1985; Torrecillas et al., 1989). Irrigation water


Table 2
Amount of water applied in the two irrigation treatments and rainfall (mm)a

Year Irrigation treatment Rainfall

T-1 T-2
b
1995 299.20 156.99 73.22
1996 624.20 277.50 367.43
1997 728.11 395.75 449.73
a
The differential irrigation experiment started on 5 July 1995.
b
Water balance started on 18 July.

was supplied daily. The annual amount of water applied is shown in Table 2, while the
characteristics of the irrigation water are shown in Table 3. The irrigation water used was
considered to be of very good quality for agricultural purposes.
To determine the water balance, eight trees were chosen: four under treatment T-1
(T1A, T1B, T1C and T1D) and four under treatment T-2 (T2A, T2B, T2C and T2D).
Two criteria were taken into account for this choice which are as follows:
1. the homogeneity and representativity of the trees and
2. the representativity of the soil texture characteristics with the trees located in zones
where the d50 approached its mean values (7:11 Æ 5:04 mm).
Thirty-two neutron probe access tubes were installed, four near each tree used in this
study (see Fig. 1). Each tube was identified according to an alphanumeric sequence that
indicated the treatment (T-1 or T-2), the replication (A, B, C or D) and the position with
respect to the trunk (1±4).
To determine the soil matric potential, trees A of each treatment were equipped with
mercury tensiometers located 40 cm from tubes 2 of each tree, and at a depth of 30, 60,
90, 120 and 150 cm.

Table 3
Main characteristics of the irrigation water

Year

1995 1996 1997 1998 Mean
pH 7.22 7.59 8.29 7.99 7.95
ECw 258C (dS mÀ1) 0.56 0.51 0.50 0.47 0.51
Total dissolved solids (g lÀ1) 0.36 0.32 0.32 0.30 0.32
Chloride (g lÀ1) 0.05 0.05 0.05 0.03 0.04
Sulphate (g lÀ1) 0.05 0.05 0.07 0.05 0.05
Bicarbonate (g lÀ1) 0.21 0.19 0.18 0.23 0.20
Calcium (g lÀ1) 0.06 0.05 0.05 0.05 0.05
Magnesium (g lÀ1) 0.02 0.03 0.03 0.03 0.03
Sodium (g lÀ1) 0.03 0.03 0.02 0.01 0.02
Potassium (g lÀ1) 0.001 0.002 0.004 0.001 0.002
SAR(adjusted) 1.03 1.01 0.50 0.45 0.74


2.3. Measurements

The soil water content was measured every 10 days from 18 July 1995 to 11 October
1996 and every 5 days from 11 October 1996 to 31 December 1997. The moisture content
was monitored at 10 cm intervals down to 1.4 m starting at 20 cm depth. The soil
moisture content of the top 10 cm of the profile was determined gravimetrically. The
program ``Aide au Traitement de Mesures Hydriques du Sol'' (AIDHYS), developed by
Laty and Vachaud (1987), was used to treat the high number of data obtained (more than
53,000).
The soil matric potential was measured once a day with mercury tensiometers from 14
February 1996 to 14 November 1997.
Daily measurements of the evaporation from the Class A pan and rainfall were made in
a field meteorological station located on the farm.
Fleming (1964) showed that the ETo calculated by Penman's equation can be
reasonably well estimated from evaporation data obtained in a Class A pan.
Â
In this way, several studies carried out in the province of Murcia (Sanchez-Toribio,
1992; Castell et al., 1987) have demonstrated that the ETo estimated from measurements
of evaporation in a Class A pan is satisfactory for the climatic conditions of this region.
The relationship between the evaporation (Eo) calculated using Penman's equation and
the evaporation measured in the pan (Epan) for the region is give by
Eo ˆ 0:86Epan À 0:53 …r ˆ 0:9769ÃÃÃ † (5)
The ETo was then calculated by multiplying the Eo obtained from Eq. (5) by an empirical
coef®cient (0.8 in summer, 0.7 in spring and autumn, and 0.6 in winter) in accordance
Â
with Sanchez-Toribio (1992).
The irrigation water supplied in each treatment was measured by volumetric counters
installed in the water supply.
Yearly, between 1995 and 1998 and coinciding with the end of the vegetative cycle, the
following measurements were taken before pruning: total height of the tree, shaded area,
and trunk diameter 30 cm above the soil surface.
The spatial representativity of the measurement sites was considered in terms of a
geostatistical analysis of soil texture and of space±time series of soil water content
measurements (Ruiz, 2000).
The time fluctuation of the mean deviation in the soil water content (the relative
deviation between the means) was determined following the method developed by
Vachaud et al. (1985a), and the correlation between the total soil water content in one
tube and the mean content of the other three tubes located in the same relative position
and on the same date, was estimated for each treatment. In all cases, linear regressions
were obtained. As regards the temporal fluctuation of the soil water content
measurements, it was observed that the total water content in all the tubes of
irrigation treatment T-1 corresponding to repetition A grossly overestimated (>30%)
the total water content with respect to the mean content. This may have been the result
of the tubes being positioned in a part of the plot with a fines granulometry
(d50 < 3 mm), and therefore, higher water holding capacity. For this reason, we
discounted this repetition.


2.4. Mass conservation law

The three-dimensional aspect of the water flow in the soil±plant±atmosphere system
means that it is essential to determine the areas and volumes of soil in which water moves
or is stored. It is customary to relate the water balance to the plantation spacing (Sharples
et al., 1985; Vachaud et al., 1985b; Moreno et al., 1988), down to a depth slightly below
that reached by the roots (1.4 m in our case).
The water balance in the soil is estimated by means of the mass conservation equation
ETc ˆ P ‡ I À DS À D À R (6)
where ETc is the evapotranspiration of the culture; P, rain; I, irrigation; DS, soil water
content variation between two dates; R, the runoff; and D, drainage (estimated using the
K(y) relationship (Eq. (1)) based on the hypothesis of a gravitational ¯ow at a depth of
1.4 m. Such a hypothesis was veri®ed by tensiometric measurements in two of the access
tubes for the neutron probe), All terms are in mm. The calculation of these terms can be
found in Franco et al., 2000.

Fig. 2. Mean water content changes down to 1.4 m depth in T1±1, T2±1, T1±4 and T2±4. Vertical lines indicate
the standard deviation.


3. Results and discussion

3.1. Effect of irrigation on soil water content

Changes in the soil water content during the experimental period are shown in Fig. 2,
which illustrates the average variation of the water content down to 1.4 m depth in the
tubes in position 2 and 4 of treatments T-1 and T-2. The zone affected (top) and not

Fig. 3. Mean water profiles in the tubes in positions 1 and 4 for both irrigation treatments in different climatic
seasons in 1996 and 1997: (*), winter; (&), spring; (~), summer; (!), autumn. The vertical lines, from left to
right, represent: wilting point, field capacity and saturation.


affected (bottom) can clearly be differentiated in this figure. The latter shows the
uniformity in water content in 1995 and 1996, while, as a consequence of the heavy rains
which fell, the soil water content varied considerably in 1997, the high values coinciding
with rainfall events. The mean overall values were 156:8 Æ 33:4 mm in T1±4 and
140:9 Æ 27:5 mm in T2±4. No difference was observed between the irrigation treatments.
As regard the wettest zone (top, Fig. 2) a seasonal behaviour was evident for both
irrigation treatments during the months of fruit set and fruit growth, when the soil water
content tended to fall in both the years studied. The mean soil water content values were
262:2 Æ 57:9 mm in T1±1 and 196:7 Æ 34:8 mm in T2±1. Although these last figures are
not significantly different, there were certain moments during fruit set and growth when
the soil water content was significantly different between treatments.
The moisture distribution profile measured four times during 1996 and 1997 was
generally little influenced by the climatic season. However, the greatest differences
occurred in the water profiles of tubes 1 in both treatments and both years (Fig. 3).
In 1996 (Fig. 3), the moisture levels in the soil of treatment T-1 during winter (30
January 1996), spring (20 May 1996) and autumn (16 November 1996) were high down
to 40 cm, beyond which the levels remained the same in winter and spring but decreased
in autumn when they reached summer levels (19 August 1996). For treatment T-2, the
high moisture levels (higher than field capacity) of the surface were maintained only in
winter, spring and autumn, falling rapidly to reach summer levels.
The soil moisture levels in 1997 (Fig. 3) reflect the higher contribution of rainfall to the
overall water level (rainfall ‡ irrigation) in this year with respect to the previous year
(9917 m3 haÀ1 in 1996 as opposed to 12,712 m3 haÀ1 in 1997). The water levels of tubes
1 in treatment T-1 show moisture levels at all depths between the field capacity and
wilting point. In T-2, the seasonal water profiles behaved similarly to T-1 although the
lower contribution of irrigation water is clear. The winter (31 January 1997) and spring
(16 May 1997) profiles were very moist in T-1 and less so in T-2. The summer (18 August
1997) and autumn (14 November 1997) profiles bahaved very similarly. The in-depth
distribution of water in both treatments in tubes 4 was similar, again reflecting the
contribution of rainfall in 1997.

3.2. Water balance

The water balance equation (Eq. (5)) was used to determine ETc in trees of the same
treatment (T-1), taking as reference the tree spacing, with the terms I, DS and D

Table 4
Weighted components of Eq. (8)

Irrigation treatment

T-1 T-2
DSÃ 20 2:22
64 ‰ 20 DS1 ‡ 17:78 DS2 Š ‡ 44 ‰1 …DS3 ‡ DS4 †Š
20 64 2
10 1:11
64 ‰ 10 DS1 ‡ 8:89 DS2 Š ‡ 54 ‰1 …DS3 ‡ DS4 †Š
10 64 2
Ã 20 2:22 17:78 44 1 10 1:11
D 64 ‰ 20 D1 ‡ 20 D2 Š ‡ 64 ‰2 …D3 ‡ D4 †Š 64 ‰ 10 D1 ‡ 8:89 D2 Š ‡ 54 ‰1 …D3 ‡ D4 †Š
10 64 2

IÃ 20
64 IT-1
10
64 IT-2


transformed into their weighted values, IÃ, DSÃ and DÃ, respectively. Using the above
results, three soil areas in T-1 and T-2 were identified with significantly different water
contents. Subsequently, models for estimating both the water content variation and the
drainage with respect to tree spacing were developed.
For the weighted soil water content variation and drainage, areas of 2.22 and 1.11 m2
were assigned to tubes 1 for T-1 and T-2, respectively. Tubes 2 were assigned areas of
17.78 and 8.89 m2 for T-1 and T-2, respectively. The average soil water content and

Fig. 4. Water inputs.


drainage of tubes 3 and 4 were used to systematically measure the same moisture
quantity, giving them areas of 44 and 54 m2 for T-1 and T-2, respectively.
Table 4 shows the mathematical expressions used to calculate the variations in the
weighted soil water content, drainage and irrigation water.
Taking into account the above weightings, the water balance equation was
ETc ˆ P ‡ I Ã À DSÃ À DÃ À R (8)
where ETc is the evapotranspiration of the culture; P, rain; IÃ, weighted irrigation dosage;
DSÃ, weighted soil water content variation; DÃ, weighted drainage, and R, runoff. All
terms are in mm.
Eq. (8) was applied every two measurement dates to each of the eight trees studied,
meaning that 120 measurements of ETc were carried out.
The water inputs as a result of rain and irrigation are shown in Fig. 4. Rain contributed
34.9 and 51.6% of the total water for treatments T-1 and T-2, respectively, during the
whole experimental period. Although globally these figures suggest a considerable
contribution of rain-water, irrigation water was the only water supplied during July 1995,

Fig. 5. Mean weighted water content variation down to 1.4 m depth in treatments T-1 and T-2. Vertical lines
indicate the standard deviation.


Fig. 6. Mean weighted drainage changes at the bottom of the profile in treatments T-1 and T-2. Vertical lines
indicate the standard deviation.

June and July 1996 and July and August 1997, which are the months of the highest
evapotranspirative demand.
The variation in the weighted quantity of water in the soil (Fig. 5) increases or
decreases as a function of rainfall or irrigation water supplied, as is revealed by both
treatments. Note how in March and April 1996, the contributions to the soil were so low
that the soil water content decreased substantially, the same as occurred in February and
March 1997, particularly in T-1.
The weighted drainage was expressed in flow units (mm per day) as a consequence of
the range of measurements, which were not constant throughout the experimental period.
The weighted drainages for both irrigation treatments are shown in Fig. 6. The differences
were statistically significant especially between February and August 1996, and between
March and August 1997, both periods coinciding with the times of greatest irrigation. For
T-1, the overall losses through drainage were 11.5% of the total contributions of water
(rainfall ‡ irrigation), while in T-2 the losses were 6.6%. If drainage is related only with
irrigation water, the losses were 17.7% in T-1 and 13.6% in T-2. The fact that volume of


Fig. 7. Runoff in T-1 and T-2 treatments.

water supplied to T-1 and T-2 treatments were 1651.5 and 830.2 mm, respectively, and the
drainage figures were 291.8 and 113.1 mm, respectively, means that 35.5% the extra
water added in T-1 drained away and was not absorbed by the root. In T-2, drainage was
low and practically constant throughout the experimental period, while in T-1, it followed
the pattern of rainfall, although with a slight delay.
Losses of water through runoff (Fig. 7) represented a high percentage of the monthly
rainfall, at times reaching 70% in T-1 and almost 50% in T-2. This is because in the area
where the experimental farm is situated such rainfall is usually intense, the whole
monthly total falling in a few days, and because the farm is on a 7.4% slope.
The evapotranspiration values for both treatments are shown in Fig. 8. These followed
similar trends each year, increasing after February to reach a maximum in May and then
falling until December±January. Since T-2 represented 50% of T-1, we wished to
ascertain to what extent this same ratio was reflected in the evapotranspiration rates of the
trees. For this, a regression analysis between the ETc of both plots was made, giving

ETc…T-2† ˆ 0:6173ETc…T-1† ‡ 0:0755 …r ˆ 0:9267ÃÃÃ † (9)


Fig. 8. Mean crop evapotranspiration changes in treatments T-1 and T-2. Vertical lines indicate the standard
deviation.

Fig. 9. Crop coefficient in treatment T-1. Vertical lines indicate the standard deviation.


Table 5
Calculated and local crop coefficients, compared with FAO recommended coefficients

Months

January February March April May June July August September October November December
Kc (cal) 0.43 0.43 0.63 0.70 0.78 0.52 0.43 0.43 0.43 0.43 0.43 0.43
Kc (local) 0.50 0.50 0.75 0.80 0.90 0.60 0.50 0.50 0.50 0.50 0.50 0.50
Kc (FAO) 0 0 0.5 0.7 0.85 0.90 0.90 0.90 0.80 0.75 0.65 0

Based on these ®ndings and in overall terms, the trees of T-2 evapotranspired 35% less
than their counterparts in T-1.
The crop coefficient was calculated by the expression
ETc
Kc ˆ (10)
ETo
Changes in the Kc values are shown in Fig. 9, in which it can be seen that Kc could not
be calculated in some periods due to the rain which fell. Since ETc equalled ETo
during periods of rain when runoff would occur, the coef®cient of Kc calculated from
Eq. (10) would be unity. This would be a ®ctitious value and so has not been
represented.
Taking into consideration the criteria of FAO (1994) to let the tree grow during its
vegetative period and to maintain the crop coefficient constant over a longish period, we
constructed Table 5 in which the mean local crop coefficients (Kc (local)), those calculated
in this experiment (Kc (cal)), and those of FAO (Kc (FAO)) are depicted. The local Kc are
those used in the area for different apricot orchards.

4. Conclusions

In the soil unaffected by irrigation, the water content behaved similarly in 1995 and
1996, while in 1997, the behaviour reflected the heavier rainfall.
In general, moisture profiles were little affected from year to year. The greatest
differences occurred in the water profiles corresponding to the tubes nearest the emitters
(tubes 1), which were most affected by irrigation.
Runoff represented a high percentage of the total water lost in both treatments,
reaching 70% in T-1 and almost 50% in T-2 in the wettest months.
Drainage losses were strongly influenced by irrigation treatment, although such losses
were never excessive, representing 11.5% of the total contribution (rainfall ‡ irrigation)
in T-1 and 6.6% in T-2.
In general terms, the trees of T-2 lost 35% less water through evapotranspiration than
the trees of T-1. The pattern of crop evapotranspiration (ETc) was similar in both
treatments, although differences were statistically significant (except in February 1996
and December 1997). The greatest differences were observed between April and
September, coinciding with the period of greatest evapotranspiration demand. Such


differences can be explained if we take into account that the evapotranspiration rate is
determined by the availability of water in the soil and the cover index. In the months of
lowest water demand, when the trees are totally bare, the ETc values are equal since the
cover index is minimal and the evapotranspiration process is dominated by soil
evaporation.
The crop coefficients, calculated on the basis of a water balance kept for 30 months,
may save up to 13% irrigation water with respect to local practices in other apricot
orchards and up 8% water with respect to FAO recommendations (Doorenbos and Pruitt,
1977).

Acknowledgements

Â Â Â Â
The authors wish to thank Mr. Jose Antonio Tomas Garcõa, and Mr. Gines Buendõa Â
Â
Gonzalez, owner and foreman, respectively, of the experimental farm for their assistance.
Â
This work was financed by projects CICYT (AMB95-71) and by the Consejerõa de Medio
Â Â
Ambiente, Agricultura y Agua de la Comunidad Autonoma de la Region de Murcia
(PS96-CA-01).

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money in young almond orchards. Calif. Agric. 36, 12±13.
Fleming, P.M., 1964. A water budgeting method to predict plant response and irrigation requirement for widely
varying evaporation conditions. In: Proceedings of the 6th International Congress Gen. Rus., Vol. 2.
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