Water balance in a young almond orchard under
drip irrigation with water of low quality
J.A. Franco
a, J.M. Abrisqueta
b,*, A. HernansaÂez
b, F. Moreno
c aDepartamento de IngenierõÂa Aplicada, Universidad de Murcia, Alfonso XIII 42 30204 Cartagena, SpainbDepartamento de Riego y Salinidad, Centro de EdafologõÂa y BiologõÂa Aplicada del Segura (CSIC),
P.O. Box 4195, 30080 Murcia, Spain
cDepartamento de Sostenibilidad del Sistema Suelo-Planta-AtmoÂsfera, Instituto de Recursos Naturales y
AgrobiologõÂa de Sevilla (CSIC). P.O. Box 1052, 41080 Sevilla, Spain
Accepted 9 March 1999
Abstract
The water balance of young almond trees (Amygdalus communis L. cv. Atocha grafted onto `PestanÄeta' almond rootstock), drip-irrigated with low quality water, was determined during two and a half years. Four irrigation treatments based on the reduction coefficients of Class A pan evaporation were used to determine the water uptake of this species, although the water balance was only determined in the highest and lowest irrigation treatments. The water balance parameters for these treatments are shown and discussed in detail. The ETc calculated for the two treatments
differed markedly during summer, reaching values of 4.3 and 3.3 mm per day (for the highest and the lowest irrigation treatments, respectively), during the last year of the experiment, coinciding with the months of highest evaporation. When various vegetative and productive parameters were studied in relation with the irrigation treatments, no clear conclusions were reached. This was mainly due to the excessive salinity of the irrigation water used (4.26 dS mÿ1), which limited the
trees' vegetative growth and production rate, which in our case was 1583 kg haÿ1compared with the 2955 kg haÿ1obtained when less saline irrigation water (0.8 dS mÿ1) and similar irrigation
water volumes (408 and 368 mm, respectively) were used for the same cultivar (Atocha).#2000 Elsevier Science B.V. All rights reserved.
Keywords: Water balance; Almond tree; Drip irrigation; Saline water
* Corresponding author. Tel.: +34-968217642; fax: +34-968266613. E-mail address:jmabrisq@natura.cebas.csic.es
1. Introduction
Spain, Italy, and USA have traditionally been world leaders in almond production. However, Italian almond production has decreased since the seventies (Barbera and Monastra, 1989), whereas the Spanish and particularly the North-American crops have increased.
In Spain almond is mainly cultivated in the Mediterranean area in both dry (92%) and irrigated plantations (8%). This high percentage of dry cultivation is due basically to the good drought-resistance of the species, which can still be productive in high water deficit situations. Indeed its irrigation has been considered not only useless but counter-productive, as was confirmed by the use in clay soils of almond scion cultivar, which is very sensitive to root asphyxia and so little tolerant of soil flooding (Barbera and Monastra, 1989).
Nevertheless, almond is a species that responds well to irrigation and behaves well under different water regimes (Fereres, 1978). Watering has been shown to be one of the most important production factors of this species, as confirmed by numerous studies reporting the positive effect of irrigation on both production and vegetative development (Micke et al., 1972; Veihmeyer, 1975; Fereres et al., 1981a, b, 1982; Shirra et al., 1988; Fereres and Goldhamer, 1990). Some of these studies have been carried out with autochthonous Murcian species (LeoÂn et al., 1985; Ruiz-SaÂnchez et al., 1988; Torrecillas et al., 1989), and many authors have attempted to define parameters of irrigation efficiency, which is particularly important when using a commodity which is both limited in supply and expensive.
Given the problems originated by water deficit in SE Spain and the low quality of this resource, it is essential to study how best to use what is available, so that the dosage can be adjusted to a minimum, with no drop in the quality or quantity of the yield.
The object of this work was to study the water balance of drip-irrigated young almond trees provided with different levels of irrigation water to achieve the above aims. We also present a model for estimating water balance parameters, taking into account both the areas which are affected and those not affected by the irrigation water. This model includes a weighted method to express changes in water storage and drainage in the mentioned areas.
2. Materials and methods
2.1. Experimental site
The experiment was carried out at a farm located 22 km SE of the city of Murcia on the Mediterranean coast of Spain (378470N; 08370W; altitude 130 m). The soil is a Xeric
torriorthent with silt loam texture, showing no variation at any of the depths studied (1.5 m). The main characteristics of the soil are shown in Table 1.
Texture characterisation was carried out from 40 profiles of soil forming a regular network. Soil samples were taken with an auger at 0.25 m intervals and with a maximum depth of 1.5 m. The granulometric composition was determined for each sample
(fractions: A, 2±0.2 mm; B, 0.2±0.05 mm; C, 0.05±0.002 mm and D< 0.002 mm), as were thed50parameter, the mean granulometrics and the meand50for each profile, and the mean values for each depth.
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 an exponential variogram model, with a sill of 1.09 (with no nugget effect) and a range of 12 m. On the map ofd50isovalues that was obtained by kriging, it was possible to detail the zone where the measuring points should be located (Franco, 1993).
A hydrodynamic characterisation of the soil was made to define the function K() of the bottom of the profile (and to enable an estimation of drainage) according to Hillel et al. (1972). TheK() relationship is given by
K210ÿ8e0:501 R20:916 (1)
where K is the hydraulic conductivity (mm hÿ1) and the volumetric water content (cm3cmÿ3).
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 almond tree(Amygdalus communisL. cvs. Atocha, Ramillete and Cartagenera grafted onto "PestanÄeta almond rootstock). These cultivars are autochthonous to SE Spain and are highly considered because of their good adaptation to different cultivation conditions and their excellent production. They flower early and their aptitude for combining with other cultivars ensures good cross pollination (Godini et al., 1991).
The trees were planted in December 1987, spaced 6 m4 m apart. The plots were drip irrigated by lines of emitters using three autocompensating emitters per tree set 1 m from each other. Each had a 4 1 hÿ1flow rate (Fig. 1). Due to the low quality water used Table 1
Main characteristics of the soil
FractionD(<0.002 mm) (%) 16.3
Fractionc(0.05±0.002 mm) (%) 59.1
FractionB(0.2±0.05 mm) (%) 20.0
for irrigation, problems occasionally arose with clogging. This was solved by periodically cleaning emitters or replacing them.
Yearly, in March or April, a cultivator (tillage depth: 10 cm) was run between tree rows to remove weeds and break the soil surface to increase its infiltrability.
All the trees in this experiment received the same fertiliser dosage, taking into account data from the literature on almond tree cultivation under localised irrigation in the Region de Murcia (Torrecillas et al., 1989). The data were adjusted when necessary in accordance with the results of the periodical leaf analyses carried out. The fertilising doses were 147 kg haÿ1N, 34 kg haÿ1P (P2O5), and 44.6 kg haÿ1K (K2O)
From May 1989, the trees were subjected to four drip irrigation treatments (T-3, T-2, T-1 and T-0) with three replications per treatment distributed in randon blocks within the same variety. The irrigation treatments were programmed using four reduction percentages of the U.S. Weather Bureau Class A pan evaporation. The reduction applied were 0, 20, 30 and 40% for T-3, T-2, T-1 and T-0 treatments, respectively.
The water applied in T-3 was considered sufficient to satisfy fully the needs of the crop (100% ETc), and to allow good rooting and tree growth, bearing in mind the susceptibility of almond trees to excess moisture, particularly at the plant neck (Hoare et al., 1974; LeoÂn et al., 1985).
The total amount of irrigation water (TIW) applied in treatment T-3 was calculated from:
TIWKpKcK1 EaEu
Epan (2)
whereKpis the pan coefficient (0.65; Doorenbos and Pruitt, 1977).Kcthe crop coefficient (0.75; Doorenbos and Pruitt, 1977).K1the shade coefficient (0.176; Freeman and Garzoli (cited by Vermeiren and Jobling, 1986), taking into account that the estimated mean shaded surface provided by the tree canopies in 1989 was 17.4% of the total surface of
the orchard),Eathe efficiency of the irrigation method (0.95; according to Guidelines for Pressure Irrigation, 1983),Euthe coefficient of uniformity of emitters (0.9).
Applying the reduction percentages mentioned above to Eq. (2) gives the following total amounts of irrigation water in each treatment:
TIW T-30:1Epan for treatment T-3 (3)
TIW T-20:08Epan for treatment T-2 (4)
TIW Tÿ10:07Epan for treatment T-1 (5)
TIW T-00:06Epan for treatment T-0 (6)
The coefficient Kl in Eqs. (3)±(6) was increased annually in accordance with the
increase in shaded area provided by the tree canopy.
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 week (Fereres et al., 1982; LeoÂn et al., 1985; Torrecillas et al., 1989). The coefficients used in the irrigation treatment schedule and the annual amount of water applied are shown in Table 2, while the characteristics of the irrigation water are shown in Table 3. Its high electrical conductivity (an average of 4.18 dS mÿ1during the experimental period) and its high chloride, sulphate and sodium content should be noted. It is clear that using such water may give rise to salinity problems in the plant and salinization of the soil because of the high sulphate content, and specific toxicity problems of medium intensity as a result of the high sodium and chloride concentrations. On the farm in which the experiment took place, irrigation was carried out with this low quality water because it was the only water available, this being the case in many others farms in the Province of Murcia. Rainfall must have helped in leaching the salt from the root zone but this point was not evaluated in detail within the framework of this study.
For determination of the water balance, six trees of cv. Atocha were chosen: three under treatment T-0 (T0A, T0B and T0C) and three under treatment T-3 (T3A, T3B and T3C).
Two criteria were taken into account for this choice:
1. The homogeneity and representativity of the trees.
Table 2
Coefficients using Class A pan evaporation and irrigation (mm, in brackets), of the four irrigation treatments. The differential irrigation experiment started on 20 May 1989
Year Irrigation treatment
T-0 T-1 T-2 T-3
1989a 0.06 (44) 0.07 (89) 0.08 (105) 0.1 (120)
1990 0.06 (44) 0.07 (103) 0.08 (106) 0.1 (110)
1991b 0.078 (111) 0.128 (212) 0.178 (273) 0.228 (329) 1992 0.101 (147) 0.171 (267) 0.242 (368) 0.314 (412) 1993c 0.131 (93) 0.245 (185) 0.370 (244) 0.487 (413)
2. The representativity of the soil texture characteristics with the trees located in zones where thed50approached its mean value (6.451.06mm).
Thirty-two neutron probe access tubes were installed: five on each chosen tree, and two more (CS1and CS2) in the centre of the zone not affected by irrigation (see Fig. 1).
Each tube was identified according to an alphanumeric sequence that indicated: the treatment (T0 or T3), the replications (A, B or C) and the position with respect to the trunk (1 to 5).
To determine the hydraulic head of the soil, trees A of each treatment were equipped with mercury tensiometers, located 40 cm from tubes 1 and 2 of each tree, and at a depth of 20, 52, 85, 117 and 150 cm.
2.3. Measurements
The soil water content was measured every 10 days using a neutron probe (Troxler mod. 4300), from 10 January, 1991 to 30 March, 1993. The moisture content was monitored at 10 cm intervals down to 1.5 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), specifically developed by Laty and Vachaud (1987), was used to treat the high number of data obtained (more than 35000).
The measurements of the hydraulic head of the soil were carried out every two days with mercury tensiometers from 12 April 1991 to 30 March 1993.
Both air temperature and air moisture were continuously recorded. Daily measure-ments of the evaporation from the Class A pan and rainfall were also 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.
Table 3
Main characteristics of the irrigation water
Year
1989 1990 1991 1992 1993 Mean
pH 7.70 7.81 7.71 7.90 7.86 7.79
SAR (adjusted) 5.41 5.22 4.51 5.33 5.19 5.14
In this way, several studies carried out in the Province of Murcia (SaÂnchez-Toribio, 1992; Castell et al., 1987) clearly showed that the EToestimated from measurements of evaporation in a Class A pan is satisfactory for the climatic condictions 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 given by
Eo0:86Epanÿ0:53 (7)
with a correlation coefficientr0.9769***
The ETowas then calculated multiplying theEoobtained from Eq. (7) by an empiric coefficient (0.8 in summer, 0.7 in spring and autumn, and 0.6 in winter) according with SaÂnchez-Toribio (1992).
The irrigation water supplied in each treatment was measured by volumetric counters installed in the water supply.
Yearly, between 1988 and 1992 and coinciding with the end of the is vegetative cycle, the following measurements were taken before pruning for the three cultivars studied (Atocha, Ramillete and Cartagenera): total height of the tree, shaded area, and trunk diameter 30 centimetres above soil surface.
Although the trees were planted in December 1987, they did not have their first significant crop until 1990, from which data production data for the three cultivars studied were recorded up to and including 1993.
Rather than replicate the measurement sites in different subplots of the T-0 and T-3 treatments, detailed measurements were taken in the trees equipped with instruments within one plot, to determine the water balance components accurately.
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 (Franco, 1993).
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 two 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 time fluctuation of the soil water content measurements, it was observed that the total water content in all the tubes of the T-3 irrigation treat-ment hardly differed from the mean content, with a maximum value of 9% in tube T2B5, while the rest exhibited values lower than 5%. In treatment T-0, it is of note that all the tubes showing soil water content values above the mean belonged to the same repetition (tree B).
2.4. Mass conservation law
The water balance in the soil is estimated by means of the equation of mass conservation:
ETcPIÿSÿDÿR (8)
where ETcis the evapotranspiration of the culture;P, rain;I, irrigation;S, water content variation between two dates;D, drainage, andR, the runoff. All terms are in mm.
2.4.1. Drainage estimation
Drainage below a depth of 1.5 m (chosen because no, or hardly any roots were found at this depth, as shown by Abrisqueta et al. (1994), Franco et al. (1995) and Franco and Abrisqueta, 1997)) was estimated using the K() relationship obtained in Section 2.1. (Eq. (1)) based on the hypothesis of a gravitatory hydraulic gradient at this depth. Such a hypothesis was verified by tensiometric measurements in four of the access tubes for the neutron probe (Fig. 2).
2.4.2. Runoff estimation
Runoff, which was considered only in periods of intense rain, was measured indirectly by assuming that in such conditions crop evapotranspiration (ETc) equals Penman's ETo, as described by Vachaud et al. (1985b) and Moreno et al. (1988). Thus the runoff (R) for the periods in which heavy rain fell occurred, was estimated from:
RPIÿSÿDÿETo (9)
2.4.3. Soil water content calculation
The soil water content down to a depth of 1.5 m was calculated by totalling the water content of individual layers of 100 mm thickness. The water content of these layers is expressed as the product of the thickness (in mm) and its volumetric water content (cm3cmÿ3). The variation in water content is represented by the difference in water content between two consecutive measurement dates as measured by neutron probe. Fig. 2. Mean hydraulic head profiles (*, TO-5; *, TO-2;&, T3-5; &, T3-2; ^, gravitatory hydraulic gradient). The horizontal lines have been omitted for greater clarity.
2.4.4. Irrigation water measurement
The difference between the readings of the volumetric counters on two consecutive dates of neutron probe measurement constituted the volume of irrigation water supplied to the trees in a given irrigation treatment.
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. 3, which illustrates the average variation of the water content down to is 1.5 m depth in the tubes in position 2 and 5 of treatments T-0 and T-3. As can be seen, the soil water content of the profile in the zone affected by irrigation changed very little in both treatments during the experimental period. However, the soil of T-3, which received most irrigation water, always stored more water, 413.626.3 mm (average) than in the least-irrigated treatment (T-0), 346.727.7 mm (average). Although these values were statistically different, the difference between them (66.9 mm) suggests that the amount of water supplied in T-0 was too high.
Fig. 3 also shows that the water content observed in tubes 2 of both irrigation treatments showed much lower variations then tubes 5. Whereas the soil water content as shown by T0-2 and T3-2 was almost constant, a clear seasonal pattern could be observed in T0-5 and T3-5, with maximum values coinciding with the most-rainy periods, and minimum values occurring during June. From the end of July, these values increased progressively due to the effect of the area wetted by irrigation, an increase which was more evident in treatment T-3. The expressions T0-2, T0-5, T3-2, and T3-5 represented the average water content of the repetitions A, B and C, for the T-0 and T-3 treatments in the tubes of position 2 and 5, respectively.
The distribution in depth of the moisture during 1992 was in general scarcely affected by seasonal changes (Fig. 4). In this figure, it can be seen that the water profiles of tubes 2 (especially in the T-3 treatment) varied less than those of tubes 5, in which the moisture differences between summer and winter were greater. These differences were particularly evident near the surface. A similar situation occurred in 1991.
The effect of the different irrigation treatments on water distribution in the soil profile during summer and winter months was evident from the water profiles corresponding to
Fig. 4. Mean water profiles of the TO-2, TO-5, T3-2 and T3-5 tubes, on six representatives dates of the experimental period (*, 7 February 1992;!, 28 April 1992;~, 8 June 1992;*, 20 August 1992;r, 29 October 1992;, 21 December 1992). The horizontal lines have been omitted for clarity.
the five tubes. At the end of winter (Fig. 5), when the soil was saturated with rain-water, the differences between the water profiles of the zone most affected by irrigation (tubes 1, 2 and 3) and those of the zone least affected by irrigation (tubes 4 and 5) were substantially smaller than during summer (Fig. 6).
3.2. Water balance
The water balance equation (Eq. (8)) was used to determine ETcin trees of the same treatment (T-0), taking as reference the tree spacing, with the terms S and D were transformed into their weighted valuesS*andD*, respectively. Using the above results five soil areas in T-0 and T-3 treatments 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.
position 5 received an area of 8 and 12 m2for treatments T-0 and T-3 respectively, tubes cs received the remaining area: 6 and 2 m2, respectively, for the two treatments.
The different weighted coefficients were calculated based on the soil areas, giving weighted water content variations referring to tree spacing, for which the mathematical expressions are:
For drainage, we proceeded in a similar way, giving tube 1 and the average of tubes 2 and 3 the same areas as those for the water content in both treatments. Since the volumetric water content measured systematically at the bottom of tubes 4 and 5 was Fig. 6. Mean water profiles for irrigation treatments T-0 and T-3 of the two summers (*, tube 1;!, tube 2;&, tube 3;*, tube 4 andr, tube 5). The horizontal lines have been omitted for clarity.
significantly similar, the mean drainage of these latter tubes was considered by giving them an area of 4 and 6 m2for treatments T-0 and T-3, respectively. The remaining area was given to tubes cs with 14 and 12 m2for treatments T-0 and T-3, respectively.
From these surface assignments, the different weighted coefficients for the drainage were calculated, giving weighted drainages referring to tree spacing, whose mathematical expressions are:
Eq. (8) was applied every two measurement dates, in each of the six trees studied, meaning that, 72 measurements of ETc were carried out.
The water inputs as a result of rain and irrigation are shown in Fig. 7. Rain contributed 78.6 and 54.9 per cent of the total water for treatments T-0 and T-3, respectively, during the whole experimental period. Although globally these figures suggest a considerable contribution of rain-water during July and August, which are the months of maximum evapotranspirative demand, the only water supplied was from irrigation.
The weighted water content variation in soil (Fig. 8) increased and decreased as a function of rainfall. Nevertheless, the decrease in the weighted water content after intense rainfall was more pronounced in treatment T-3 than in treatment T-0.
The weighted drainage was expressed in flux units (mm per day) as a consequence of the range of measurements, which were not constant through the experimental period. The weighted drainages for both irrigation treatments are shown in Fig. 9 with clear differences being observed between them. For T-0, the overall drainage losses were 5.7% of the water supplied (rainirrigation), whereas for T-3, the losses were 35.3%. As regards the water added by irrigation, drainage losses were 22.3% for T-0 and 67.2% for T-3 Since the volume of water supplied to T-0 and T-3 treatments was 359.2 and 1154.1 mm respectively, and the drainages were 80.4 and 775.8 mm, respectively, the excess water supplied in treatment T-3 was practically all drained (87.5%) and not absorbed by the roots. While for treatment T-0 drainage was practically null during the whole experimental period, the time course of T-3 drainage was similar to that observed after heavy rain observed.
Another aspect worthy of note is that the tree canopy size (and hence its soil covering index) and the soil water extracted by the roots seemed to be unaffected by the irrigation treatments and so it can be assumed that transpiration did not differ significantly. Thus, the differences observed between the ETcvalues of the two treatments could be attributed to evaporation from the soil surface as affected by the irrigation, which was, of course, greater in treatment T-3 than in T-0.
irrigation treatments are shown in Fig. 11. Similar behaviour was observed for both treatments throughout the experimental period, with maximum ETcvalues during spring-summer and minimum values during autumn-winter. There was a marked decrease in the ETcvalues between April and May 1992, from 2.9 mm per day in April to 1.2 mm per day in May for treatment T-0, and from 3.1 mm per day to 1.8 mm per day in treatment T-3. This can be explained by the rain which fell in May 1992 (60 mm), which decreased the evapotranspirative demand as a consequence of the cloud cover. The situation was similar in March 1993, although in this case the decrease was less marked despite the fact that the rainfall was similar (65 mm). It is also important to highlight the final stages of the experiment when the ETcvalues remained constant during June and July in treatment T-0, they but increased from April onwards in T-3. This could only have been a
Fig. 7. Water inputs
consequence of the 22.3% higher water inputs from the irrigation in this treatment, since the rain can be considered a non-significant contributor (except during May when 45.9 mm fell).
Table 4 and Table 5 show the average seasonal terms of Eq. (8) for T-0 and T-3 treatments, respectively.
3.3. Effect of irrigation on the vegetative development and yield
Table 6 shows trunk diameter values, measured 30 cm above the soil surface for the three almond cultivars and irrigation treatments. The tree trunk diameter of Cartagenera cultivar showed no significant differences between irrigation treatments in any year of the experiment. In contrast, the trunk diameters of Atocha differed significantly between treatments T-0 and T-3 in both 1989 and 1990. In 1991, the trunk diameter of T-0 trees of this cultivar was significantly different from T-2 and T-3 trees. The trunk diameter of T-0 Ramillete cultivar trees was significantly different from T-3 trees throughout the four years of the experiment. This cultivar always showed higher trunk diameter values than the other two cultivars in the T-3 treatment.
trees were significantly tall in treatment T-3 than in T-0 in 1989 and 1992. The tree height values for Atocha cultivar were always greater in T-0 than in the other treatments, the difference between T-0 and T-3 treatments being statistically significant in 1990 and 1992.
Fig. 9. Mean weighted drainage changes at the bottom of the profile in treatments T-0 and T-3. Vertical lines indicate the standard deviation.
Table 4
Average seasonal terms of Eq. (8) for T-0 treatment (mm per month)
Season P I S* D* R ETc ETo
Winter/91 76.2 0.6 ÿ5.5 7.5 34.8 38.8 24.0
Spring 6.0 12.0 ÿ36.0 3.4 0 50.5 91.6
Summer 5.6 18.3 ÿ10.3 0.4 0 34.3 146.8
Autumn 26.4 6.1 0.3 0.5 8.5 23.3 30.9
Winter/92 56.8 3.0 1.1 2.0 32.0 24.2 19.6
Spring 50.9 14.1 ÿ11.6 1.8 17.2 57.2 75.8
Summer 2.5 22.2 ÿ14.8 0.5 0 39.5 117.0
Autumn 37.9 9.7 10.6 0.8 17.6 18.4 43.8
Winter/93 69.4 4.3 ÿ8.3 6.4 37.3 37.5 14.1
Spring 16.0 19.6 ÿ21.7 3.0 5.3 51.9 99.9
In treatment T-0, significant difference in tree height was observed between Cartagenera and Ramillete cultivars in 1989, and between Atocha and Ramillete in 1992. Tree height was always significantly different between Cartagenera and Atocha cultivars in treatment T-0, except in 1991. In treatment T-3, significant differences in tree height were also observed between cultivars, except in 1992.
Fig. 10. Runoff in T-0 and T-3 treatments.
Table 5
Average seasonal terms of Eq. (8) for T-3 treatment (mm per month)
Season P I S* D* R ETc ETo
Winter/91 76.2 1.6 ÿ12.1 36.3 20.5 31.3 24.0
Spring 6.0 35.2 ÿ20.8 17.6 0 44.2 91.6
Summer 5.6 55.6 ÿ6.1 11.7 0 56.6 146.8
Autumn 26.4 17.1 9.3 6.8 7.2 23.4 30.9
Winter/92 56.8 7.9 ÿ9.5 15.1 29.4 29.3 19.6
Spring 50.9 30.8 ÿ40.8 21.2 19.1 78.7 75.8
Summer 2.5 62.2 ÿ11.1 7.8 0 69.4 117.0
Autumn 37.9 36.1 6.2 36.6 18.1 13.3 43.8
Winter/93 69.4 18.7 ÿ23.5 45.4 34.9 30.1 14.1
Fig. 11. Mean crop evapotranspiration changes in treatments T-0 and T-3. Vertical lines indicate the standard deviation.
Table 6
Diameter of tree trunk (cm) measured 30 cm above the soil surface
Cultivar Irrigation treatment
T-0 T-1 T-2 T-3
1989
Cartagenera 3.8 a 4.1 4.1 4.2 a
Atocha 4.8 b(2) 4.2 (1) 3.9 (1) 3.8 a(1)
Ramillete 4.4 b(1) 4.1 (1) 3.5 (1) 5.7 (2)
1990
Cartagenera 6.8 6.7 6.0 6.3 a
Atocha 7.2 (2) 6.1 (1) 5.3 (1) 5.3 a(1)
Ramillete 6.5 (2) 5.7 (1,2) 5.3 (1) 9.0 b(3)
1991
Cartagenera 9.0 8.1 7.9 8.4 a
Atocha 10.2 (2) 8.8 (1,2) 7.9 (1) 8.2 a(1)
Ramillete 8.7 (1) 7.9 (1) 8.1 (1) 11.3 b(2)
1992
Cartagenera 10.2 a 10.1 9.6 10.4 a
Atocha 12.0 b 11.0 10.6 10.5 a
Ramillete 10.7 (1) 10.5 (1) 10.7 (1) 13.6 b(2)
Values in each line followed by the same number in brackets are not significantly different (P< 0.05). Values in each column followed by the same letter are not significantly different (P< 0.05).
Table 7 Tree height (m)
Cultivar Irrigation treatment
1989 T-0 T-1 T-2 T-3
Cartagenera 2.31 a 2.56 2.56 2.58 a(1,2)
Atocha 2.80 b(2) 2.68 (2) 2.37 (1) 2.55 a(1,2)
Ramillete 2.68 ab(1) 2.78 (1,2) 2.61 (1) 3.11 b(2) 1990
Cartagenera 3.15 a 3.18 2.93 a 2.95 a
Atocha 3.60 b(2) 3.20 (1) 2.83 a(1) 2.93 a(1)
Ramillete 3.33 ab 3.23 3.58 b 3.67 b
1991
Cartagenera 3.68 3.68 3.20 a 3.45 a
Atocha 4.10 (2) 3.60 (1) 3.63 ab(1) 3.75 ab(1,2)
Ramillete 3.61 3.80 3.85 b 4.00 b
1992
Cartagenera 4.38 a 4.46 3.86 a 4.25
Atocha 4.96 b(2) 4.55 (1,2) 4.70 b(1,2) 4.38 (1) Ramillete 4.05 a(1) 4.28 (1,2) 4.65 b(2) 4.60 (2)
Values in each line followed by the same number in brackets are not significantly different (P< 0.05). Values in each column followed by the same letter are not significantly different (P< 0.05).
Table 8 Area shaded
Cultivar Irrigation treatment
T-0 T-1 T-2 T-3
1989
Cartagenera 2.97 3.88 b 3.40 b 3.61 b
Atocha 3.10 (2) 2.28 a(1) 1.97 a(1) 1.67 a(1)
Ramillete 3.99 (2) 2.04 a(1) 2.33 ab(1) 7.26 c(3)
1990
Cartagenera 6.23 a 6.71 4.54 ab 5.88 a
Atocha 5.63 a(2) 4.18 (1,2) 3.03 a(1) 3.56 a(1)
Ramillete 8.69 b(2) 4.44 (1) 7.40 b(1,2) 13.53 b(3)
1991
Cartagenera 8.57 a 9.96 b 6.93 ab 8.94 a
Atocha 8.52 a(2) 6.74 a(1,2) 5.13 a(1) 5.75 a(1)
Ramillete 12.94 b(2) 7.l2 ab(1) 10.63 b(1,2) 17.48 b(3)
1992
Cartagenera 12.28 13.08 10.57 ab 11.46 a
Atocha 11.74 11.44 8.82 a 10.00 a
Ramillete 12.41 (1) 10.77 (1) 15.00 b(1,2) 19.18 b(2)
Table 8 shows the results of the measurement of the area shaded by the trees. For Ramillete cultivar, significant differences were observed between irrigation treatments. The shaded area was significantly higher in treatment T-3 than in T-0 in the four years of the experiment. The area shaded by the trees of Cartagenera cultivar did not show significant differences between irrigation treatments, this parameter apparently not being affected by the irrigation treatment in this cultivar. In the case of Atocha cultivar, on the other hand, the shaded area was significantly lower in treatment T-3 than in T-0 during the first three years of the experiment.
The yields of almond for the different irrigation treatments are shown in Table 9. It can be seen that there were no significant differences between irrigation treatments in any year of the experiment. The only significant difference was between Cartagenera and Atocha cultivars for the T-0 treatment in 1989.
In general, then, the amount of water supplied by the different irrigation treatments affected the different vegetative parameters differently, depending on the cultivar, but no clear relationship could be established or any firm conclusion reached.
Many authors have described the markedly positive effect of an increase in water supply on almond tree production (Fereres et al., 1982, 1990), and some papers on the use of autochthonous Murcian cultivars have also reported such an effect (LeoÂn et al., 1985, Torrecillas et al., 1989). However, our results, do not permit us to infer any significant effect of the amount of water supplied on production. Nor did Andriani et al. (1989)
Table 9
Total yield of almonds (kg per tree)
Cuitivar Irrigation treatments
T-0 T-1 T-2 T-3
1990
cartagenera 0.60 b 0.28 0.42 0.29
Atocha 0.18 a 0.18 0.15 0.25
Ramillete 0.51 ab 0.40 0.70 0.52
1991
Values in each line followed by the same number in brackets are not significantly different (P< 0.05). Values in each column followed by the same letter are not significantly different (P< 0.05).
observe differences in production when using water regimes involving the application of from 50 to 100% of the ETo.
The almond is a species with a limited tolerance of salinity (Maas, 1984, 1986; Shiskov and Kapshuk, 1987; Hassan and EI-Azayen, 1990; Nightingale et al., 1991). The low yields obtained in this experiment were due to the high salinity of the water used for irrigation (Table 3) that originated a decrease of the mean potential yield (calculated on the basis of tree development) of about 90%. According to Ayers and Westcot (1976) the almond tree is very sensitive to salinity and its mean potential yield with poor quality water may be about 10% of the yield that can be obtained when irrigation is carried out with good quality water.
In the last year of the study, production was only 2.1- and 2.6-fold (for Ramillete and Atocha, respectively) of the average production obtained in dry cultivation, compared with an average increase of almost 10-fold, when good quality water was used for irrigation.
Table 10 shows the results of the yield obtained in this experiment for Ramillete and Atocha cultivars, and those reported by Torrecillas et al. (1989) for the same cultivars drip-irrigated with similar amounts of water of good quality. In the experiment reported by Ruiz-SaÂnchez et al. (1988) the trees were of the same age and size as in our experiment, and grew under similar conditions of soil and climate in the Province of Murcia. A comparison of these results clearly demonstrates the effect of saline irrigation water on the yield of almond trees.
The production losses observed are in good agreement with those reported by Maas (1984) and by Ayers and Westcot (1976) in connection with the sensitivity of almond to irrigation water salinity.
4. Conclusions
During the estimation of the water balance, the soil water content of the zone affected by irrigation remained practically constant, independently of the water dosage applied (although it is was slightly higher in the most-irrigated treatment). This suggests that even Table 10
Comparison of total yield of almonds (kg per tree) for Ramillete and Atocha cultivars with yield data reported by Ruiz-SaÂnchez (1988)
Treatments Irrigation water Yield (kg per tree)
(mm per year) Ramillete Atocha
the less-irrigated treatment (T-0) was adequately watered. The soil water content in areas not affected by irrigation followed a seasonal pattern in accordance with the evaporative demand.
A high percentage of the water supplied as rain was lost by runoff, such losses reaching more than 70% in the months of intense rain. The loss though water drainage differed markedly in the different irrigation treatments. In treatment T-0 the estimated drainage was 4.5% and only acquired relevance in the periods following intense rainfall. In contrast, in treatment T-3, the estimated drainage was 41.5% of the total net water supply recorded.
The difference in water lost though drainage between the most- and least irrigated treatments during the whole experimental period (695 mm) represents about 87.5% of the difference in water applied by irrigation in both treatments (795 mm). This clearly indicates that only 12.5% of this water was used by the trees in treatment T-3.
In the case of this young almond orchard it seems that only treatment T-0 provided the adequate amount of water. In contrast, the other treatments particularly treatment T-3 provided too much water. The estimated ETcfor the months from October to May was not significantly affected by the irrigation treatment. However, during the summer months some important differences were observed in the ETcvalues. These differences were greater during June and July, which could be attributed to the larger wet area of the soil in the most-irrigated treatment, from which more water was lost through evaporation. This is supported by the fact that the size of the tree canopies, and hence, the soil coverage index, and the root extraction of water from soil were not affected by the irrigation treatments, meaning that the trees transpiration rates were similar.
The low productions and the non significant results obtained when comparing different parameters (both production and vegetative) for the irrigation treatments can clearly be attributed to the use of low quality irrigation water.
These results, it is hoped, may be of use when designing irrigation strategies for young almond orchards located in areas with scarce and/or low quality water resources.
Acknowledgements
The authors wish to thank Mr. RamoÂn Navarro GoÂmez and Mr. TomaÂs Bautista Soto, owner and foreman, respectively of the experimental farm for their assistance. This work has been financed by projects CICYT (AGR 89 0496), EC-8001-CT91-0301, and by the ConsejerõÂa de Agricultura, GanaderõÂa y Pesca de la Comunidad AutoÂnoma de la RegioÂn de Murcia.
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