Effect of Water salinity and Irrigation Technology on Yield ... - CiteSeerX

Biosystems Engineering (2002) 81 (2), 237}247 doi:10.1006/bioe.2001.0038, available online at http://www.idealibrary.com on SW*Soil and Water

E!ect of Water Salinity and Irrigation Technology on Yield and Quality of Pears Gideon Oron; Yoel DeMalach; Leonid Gillerman; Itsik David; Susan Lurie The Institute for Desert Research, Ben-Gurion University of the Negev, Kiryat Sde-Boker 84990, Israel Department for Industrial Engineering and Management, Beer-Sheva 84105, Israel; e-mail of corresponding author: [email protected] Ramat Negev Agricultural Field Station, Doar-Naa Chalutza 85415, Israel; e-mail: [email protected] Agricultural Research Organization, The Volcani Center, The Institute for Technology and Storage of Agricultural Products, Bet-Dagan 50250, Israel; e-mail: [email protected] (Received 8 November 2000; accepted in revised form 9 November 2001; published online 28 January 2002)

The scarcity of fresh water in arid regions makes saline water a valuable alternative water source for irrigation. Saline water has an agricultural potential but it is necessary to develop special management procedures to obtain maximum yield and high product quality. Field experiments, which were carried out in a pear orchard, demonstrate that the choice of irrigation method is very important for saline water irrigation. It was shown that by using saline water through subsurface drip irrigation (SDI) reasonable yields can be obtained. Moisture distribution under SDI is better adjusted to the root pattern in order to counteract osmotic e!ects of the soil salinity in comparison to conventional drip irrigation. Saline water use, particularly through SDI, tends to increase sugar content and acidity of the fruits simultaneously, along with decreasing fouling phases. 2002 Silsoe Research Institute

1. Introduction Most areas in the state of Israel, which is located in an arid zone, are characterized by scarce water resources. High-quality water resources available for use in agriculture are decreasing due to growth of population and increasing of living standards. It has led to use lowquality waters (e.g. treated wastewater or saline water) in agriculture simultaneously with implementation of the most e$cient application technologies. In the Northern Negev of Israel, there is an aquifer that contains several hundred billion m of saline water (Issar & Nativ, 1988). The salinity of the water varies in the range of electrical conductivity (EC) between 4 and 7 dS m\ (Tscheschke et al., 1974; Twersky et al., 1975) while fresh water is commonly below 2 dS m\. Until recently, this water was not actually used for agricultural irrigation in Israel. However, fresh water resources are becoming scarce and have to be replaced with unconventional water sources, in particular with saline water (Oron, 1993). Utilization of saline water for irrigation is associated with salt accumulation in the soil, which might be harmful to plants, and diminishing yields. The salt e!ects on 1537-5110/02/020237#11 $35.00/0

physiological process result from lowering of the soil water potential and the toxicity of speci"c ions (Bresler et al., 1982). On the other hand, it has been repeatedly reported that non-toxic highly saline water has an agricultural potential. If irrigation can be managed in a way which provides a high soil moisture content and, consequently, high soil water potential within the whole root zone, the osmotic e!ects will be damped (Bernstein & Fancois, 1973; Tsheschke et al., 1974; Michelakis et al., 1993). Moreover, when saline water is skillfully used for irrigation, it can be bene"cial for agricultural production, particularly in orchards (Ho!man et al., 1986). Saline water use for agricultural production o!ers several additional bene"ts: (1) re-use (instead of disposal as with fresh water) during the entire year, with minimal environmental risk of groundwater deterioration (Oron, 1993); and (2) a premium market price for the fruits and vegetable products because of a high content of total soluble solids and an extended shelf life, due to the adaptation of the plant to the stressful growing conditions (Mizrahi & Pasternak, 1985).

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2002 Silsoe Research Institute

238

G . O R O N E¹ A ¸.

Applying saline water continuously through drip irrigation systems might result in salt accumulation close to the soil surface (Bresler et al., 1982; Ayers & Westcot, 1985; Pasternak & DeMalach, 1987; DeMalach & Pasternak, 1993; Oron et al., 1995). Under conventional surface drip irrigation (DI), during precipitation and uniform distribution on the soil surface, the salts that are accumulated close to the soil surface can migrate downwards and reach the main root zone. This process may inhibit water and nutrient uptake, consequently causing adverse e!ects on the crop growth and yield (Hanson & Bendixen, 1995). In order to o!-set the osmotic shock imposed on the crop by the leached salts (surface drip irrigation systems during precipitation), a practical solution was proposed. It is a common practice in arid regions to maintain equilibrium conditions in the soil, and to keep the salt front in a permanent position in the periphery of the root zone by continuing drip irrigation during the periods of precipitation (Hanson, 1995). The water in"ltrating into the soil during precipitation is not shifting the salt front due to the opposing e!ect of the water emitting from the subsurface water source (the emitter). Alternatively, Oron et al. (1990, 1991) and Phene (1993) have suggested that this problem can be overcome by applying saline water through a subsurface drip irrigation (SDI) system. It is anticipated that under SDI, the salt front is driven deeper into the soil bulk medium and to the periphery of the root zone, thus minimizing the risk of damaging the plants. Likewise, Phene & Phene (1987) reported that since the SDI is installed below the soil surface, a properly managed system (primarily by frequent irrigation) is advantageous in comparison with conventional DI systems, especially with regard to e$cient water and nutrient utilization, salinity management and deep percolation. The purpose of this study was to evaluate the e!ect of di!erent water qualities and drip irrigation systems (DI and SDI with emitters located at variable depths in the soil) use on the yield and fruit quality. The possibility of using saline water through SDI for fruit tree irrigation is being examined in the "eld in a pear orchard.

2. Materials and methods 2.1. ¹he experimental site The experiment was being conducted at the Ramat Negev Agro-Research Centre, located about 35 km south-west of the City of Beer-Sheva, Israel (longitude 3434103 and latitude 3130500). The mean annual rainfall in the region is about 102 mm spread over four rainy months (November through February). Mean maximal ambient temperature reaches about 34)93C during July

and August and mean minimal temperature is close to 5)43C during January. The relative humidity during summer months varies from 20% to 30%. Annual class &A' pan evaporation is about 2294 mm. The experimental soil is a light loess (sandy loam), consisting of 51)4% silt, 8)8% clay and 39)8% sand. The moisture content at "eld capacity is approximately 24% by volume. 2.2. ¹he experimental layout The possibility of using SDI for saline water application was examined in a pear orchard. Spadona pear (Pyrus spp.) trees, arranged in six rows, were planted in 1982 at a row spacing of 5 m and inter-row spacing of 2)5 m. One drip lateral served every pear row with emitters spaced 75 cm apart and having a discharge of 4 l h\. Prior to commencement of the experiment (from 1982 until 1992) the trees were irrigated by a conventional onsurface DI system. Current research began in March 1993 with the following treatments: (1) three rows were irrigated with saline water having an EC of about 4)4 dS m\; and (2) three control rows were irrigated with fresh highquality tap water with an electrical conductivity of 1)2 dS m\. Each row consisted of three treatments with two replications: (i) surface DI; (ii) SDI with emitters located at a soil depth of 30 cm; and, (iii) SDI with emitters located at 60 cm soil depth. Only the central row out of the three was examined in each replication. Although a "eld experiment consisting of two replications only might lead to false interpretation of the results, it was decided to conduct the research in an available pear plantation despite the reduced number of replications, in order to obtain preparatory information which would lead to a more detailed and well organized experiment. The SDI was maintained by connecting small diameter (4 mm diameter) microtubes (&spaghetti') to the on-line emitters and inserting them into the soil up to the designated depths of 30 and 60 cm. This arrangement was implemented in order to avoid a signi"cant intrusion into the tree root zone and, consequently, to minimize potential damage to the crop by converting the conventional surface DI system to a SDI system. Special attention was paid during the initial research phases in order to prevent water up-#ow in the &chimney' into which each &spaghetti' tube was inserted. 2.3. =ater application During 3 years of experimentation, the crop received equal volumes of irrigation water amounting to

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EF FEC T O F WA TE R SA L I NI T Y AN D I RR I G A TIO N TEC H N O LO G Y O N P EA R S

on both sides near emitter and in the middle between two adjacent emitters. The corresponding depths were 0}10, 20}30, 60}70 and 90}100 cm. A similar monitoring layout was used for the soil sampling at half the distance between the emitters.

2.5. Pear yield and fruit quality monitoring

approximately 900 mm (Fig. 1). Water application commenced towards the end of February and continued up to October. During the peak consumption period (May to July), the irrigation interval was 3}4 days in order to maintain adequate soil moisture in the e!ective crop root zone. During the remaining months, the irrigation interval was seven days. Irrigation scheduling was based on Class &A' pan evaporation measurements, multiplied by the locally developed crop coe$cients for pear plantations (Table 1; DeMalach & Pasternak, 1993).

2.4. Moisture and salinity monitoring in the soil Soil moisture and salinity distribution in the soil at di!erent depths in every treatment was monitored periodically, following standard procedures. Soil moisture content was measured by a standard gravimeteric method. Soil salinity was determined by a common method of measuring the electrical conductivity (EC) of the saturated extracts. During the peak consumption period (June to August) soil moisture and salinity were measured once a month. Soil samples for moisture and salinity assessment were taken at 0, 20, 40, 60 and 80 cm radially from the lateral

The pears were hand harvested for the yield assessment during July of the years 1993, 1994 and 1995. The pear yields were measured by weighing the fruits immediately after harvest in the "eld. The signi"cance of the yield di!erences was determined by one-tailed &t'-test at 95% signi"cance level. The quality of the fruits was further monitored for the harvests of 28, 26 and 23 July of 1994, 1995 and 1996, respectively (the pear quality was not assessed for the 1993 harvest since the testing equipment became available only for the 1994 harvest; the 1996 harvest was towards the end of the experiment with relatively poor results, hence it was decided not to include the yield in the analysis, to characterize the fruit quality). For fruit quality parameters determination, three samples of ten fruits per treatment were sampled at each observation time for the 1994 and 1995 harvest (only one sample of 15 fruits was taken for the 1996 harvest). Pear "rmness was measured on two peeled sides of each fruit using a penetrometer with an 8 mm tip. Soluble solids content (SSC) (a measure for sugar content) and titratable acidity (TA) were measured by pooling a slice from each fruit in the replicate and juicing them. The soluble solids were measured with refractometer. The TA was determined by taking 2 ml of the juice, titrating it to pH

Soil moisture content, % v/v 0 10 20 30 40 0

Table 1 Crop coe7cient Kc used for pear orchard irrigation Month February March April May June July August September October

K

A

0)20 0)20 0)35 0)55 0)65 0)70 0)50 0)35 0)20

Soil depth, cm

20 40

Soil moisture content, % v/v 0 10 20 30 40 0 20 40 DI

DI

60

SDI 30 cm deep SDI 60 cm deep

80 100 120 140

Soil depth, cm

Fig. 1. Monthly amounts of water applied for irrigation of the pear orchard

60 SDI 30 cm deep SDI 60 cm deep

80 100 120 140

160

160

180 200

180 200 (a)

(b)

Fig. 2. Soil Moisture proxles below the emitter for on-surface (DI) and subsurface drip irrigation (SDI) for: (a) fresh water irrigation; and (b) saline water; ( ), anticipated optimum range of soil moisture content

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Fig. 3. Soil moisture (% v/v) distribution in the pear orchard subject to diwerent depths of emitter location and saline water application, 18 June 1994, 10 h after irrigation termination; (a) onsurface drip irrigation; (b) subsurface drip irrigation (emitter depth 30 cm); (c) subsurface drip irrigation (emitter depth 60 cm); ( ), emitter location

3.1. Moisture distribution in the soil The "eld data provided information characterizing the moisture distribution in the soil (Figs 2 and 3). According to results, SDI with the emitter installed at a depth of 30 cm, consistently ensures favourable soil moisture conditions for the pear trees both in terms of amount and uniformity. The soil moisture content varies in the range of 18% (approximately 25% below the "eld capacity soil moisture content) to 24% ("eld capacity moisture content). On the other hand, conventional DI facilitates optimal moisture content primarily in the upper soil layer. The lower part of the root zone, which is commonly considered to be up to a depth of 100 cm (Stegman et al., 1983) is subject to inadequate moisture conditions. For example, the moisture distribution pattern under conventional DI is probably inferior for pear trees growth in comparison with SDI system that is installed at a depth of 30 cm. Likewise, the soil moisture distribution under SDI with emitters located at a depth of 60 cm was neither uniform nor did it induce good crop growth, since it is

3.2. Salinity distribution in the soil Salinity in the soil as expressed by electrical conductivity distribution also exhibits trends similar to that of the soil moisture irrespective of the water quality used for irrigation (Figs 4 and 5). For the emitters located 30 cm deep, extremely high salinity (16}20 dS m\) was recorded only in the "rst few centimetres close to the soil surface, similar to the previous "ndings (Hanson &

Soil electrical conductivity, dS m−1 Soil electrical conductivity, dS m−1 0 1 2 3 4 5 6 0 2 4 6 10 11 12 14 0 0 20 20 DI 40 40 DI SDI 30 cm 60 SDI 30 cm 60 deep deep 80 80 SDI 60 cm 100 100 SDI 60 cm deep deep 120 120 140 140 160 160 180 180 200 200 (b) (a) Soil depth, cm

3. Results

associated with increased deep percolation losses. Thus, the active root zone remains relatively dry and the lower layers of the root zone contain high moisture resulting in ine$cient use of the applied irrigation water.

Soil depth, cm

8)2 with 0)1 NaOH and expressing the result as malic acid. The fruits were measured at harvest and subsequently after 5 months storage at !13C air temperature, and later following 7 days shelf life at 203C. Rots and the internal #esh disorder, core#ush, were determined visually after halving each fruit at the end of shel#ife. The signi"cance of the results, at 95% con"dence level, for the di!erent treatments was determined with the Duncan multi-range test.

Fig. 4. Soil salinity proxles below the emitter subject to diwerent water qualities and depths of emitter locations: (a) fresh water; and (b) saline water; DI, surface drip irrigation; SDI 30, subsurface drip irrigation at a depth of 30 cm; SDI 60, subsurface drip irrigation at a depth of 60 cm


241

Fig. 5. Salinity distribution contours for electrical conductivity in dS m!1 in a pear orchard as a function of emitter location depth, June 1993 (one day after irrigation termination) for: (a) tap water irrigation; and (b) saline water irrigation; each for (i) surface drip irrigation; (ii) subsurface drip irrigation at a depth of 30 cm; (iii) subsurface drip irrigation at a depth of 60 cm; ( ), emitter location

Bendixen, 1995; Or, 1996). On the other hand, in the immediate vicinity of the emitter, i.e., in the active root zone depth of the crop, the salinity (expressed by the EC) varies within a narrow range from 3 to 5 dS m\. It is anticipated that SDI maintains continuous soil leaching phases not only downwards, but also upwards and radially. Therefore, for emitters located at a depth of 30 cm the salts in the irrigation water and those initially contained in the soil were displaced to the periphery of the root zone. Therefore, the soil salinity in the main active zone was approximately equivalent to the salinity of the applied water. On the other hand, as expected, the conventional DI facilitated su$cient leaching just below the emitter in the top soil layer, contributing to extra accumulation of salts in the active root zone of the crop. Thus, the soil salinity level remained fairly high in deep

soil layers (more than 80 cm deep) under the conventional DI system. Likewise, the leaching process was more e!ective downwards towards the lower soil layers while the upper ones remained relatively dry, for the emitter located at a depth of 60 cm (Fig. 4). For emitters at a depth of 60 cm, salt accumulated in the top layers, leading to a salinity higher than in the water applied for irrigation.

3.3. >ield According to the "eld results, relatively high pear yields for both water qualities were obtained when the emitters were located at a depth of 30 cm below the soil surface (Fig. 6). The yield with fresh water for the

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G . O R O N E¹ A ¸.

Fig. 6. Ewect of emitter location and water quality on pear trees yield for: (a) tap water application; and (b) saline water application; ( ), surface drip irrigation; ( ), subsurface drip irrigation at a depth of 30 cm and, ( ), subsurface drip irrigation at a depth of 60 cm

treatment with emitters 30 cm deep is higher by 11}19% than for conventional on-surface DI. Similarly, the yield with saline water and emitters at a depth of 30 cm was higher by 32}40% than for on-surface DI. However, the crop under conventional surface drip system performed better in terms of yield (9}11% for fresh water and 36}40% for saline water irrigation) in comparison to the yields obtained for SDI with emitters located 60 cm deep. The di!erences in yields obtained in the present study are somewhat inconsistent, primarily due to the diverse moisture content and salinity in the root zone (Ayers & Westcot, 1985). The di!erences with the yields of various treatments were further analysed by the one-tailed &t'-test for 95% signi"cance level (Tables 2}4). Four samples were used for assessing the pear yield for every treatment and for calculating the &t' values. The calculated &t' was compared with

the tabulated &t' for six degree of freedoms [two treatments with four replications each namely, t (6)"1)94]. The results indicate the advantage of SDI at a depth of 30 cm, both for the fresh and saline water. There is a clear evidence that saline water application at a depth of 30 cm is much better than on-surface application. Based on the conventional approach which concerns the mean amount of water stored in the crop root zone and the mean salinity level (Maas & Ho!man, 1977; Stegman et al., 1983; Shalhevet, 1994), presented in Table 5, the large di!erences in the yields obtained in present experiment (Fig. 6) are somewhat perplexing. Analyzing the data regarding mean soil moisture content and average soil salinity in the root zone during the active growing season found negligible di!erences between the treatments (Table 5). This observation, therefore, gave rise to the speculation that the observed yield

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Table 2 The pear yields for the 1993 harvest and 95% signi5cance level implementing one-tailed 9t ’-test analysis for assessing the di4erences between the treatments Treatment*

Yield $SD*, Mg ha!1

Yield $SD*, Mg ha!1

Calculated *t+

Non-signixcant and signixcant diwerences at t0)95(6)"1)94

30 fresh}0 fresh 0 fresh}60 fresh 30 fresh}60 fresh

86)4$14)8 72)0$10)2 86)4$14)0

72)0$10)2 65)6$9)1 65)9$6)1

1)60 0)94 2)56

Non-signi"cant Non-signi"cant Signi"cant

30 sal}0 sal 0sal}60 sal 30sal}60 sal

74)9$11)8 55)0$8)6 74)9$11)8

55)0$8)6 49)0$7)9 49)0$7)9

2)73 1)03 3)65

Signi"cant Non-signi"cant Signi"cant

0 fresh}0 sal 30 fresh}30 sal 60 fresh}60 sal

72)0$10)2 86)4$14)8 65)6$9)1

55)0$8)6 74)9$11)8 49)0$7)9

2)55 1)22 2)76


30 sal}0 fresh

74)9$11)8

72)0$10)2

0)37

Non-signi"cant

*Fresh, fresh water; sal, saline water; 0, surface drip irrigation; 30, 60, Subsurface drip irrigation at 30 and 60 cm depths, respectively; SD, standard deviation.

di!erences might be due to variations in the soil moisture distribution pattern (which can also counteract the osmotic e!ects) and might a!ect the salt distribution rather than the amount per se. 3.4. Fruit quality According to the results (Tables 6}9) applying saline water has several advantages in regards to the fruit qual-

ity parameters. Applying saline water under SDI even improves the fruit quality.

3.4.1. Firmness of fruits No signi"cant di!erence in "rmness of the fruits can be identi"ed for the three harvesting years (Tables 6}9). That is also the case for fruits after 5 months of storage under temperature conditions of !13C.

Table 3 The pear yields for the 1994 harvest and 95% signi5cance level implementing one-tailed 9t:-test analysis for assessing the di4erences between the treatments Treatments*

Yield $SD*, Mg ha!1

Yield $SD*, Mg ha!1

Calculated *t+

Non-signixcant and signixcant diwerences at t0)95(6)"1)94

30 fresh}0 fresh 0 fresh}60 fresh 30 fresh}60 fresh

62)6$13)9 55)8$8)4 62)6$13)9

55)8$8)4 36)3$8)4 36)3$8)4

0)84 3)28 3)24

Non-signi"cant Signi"cant Signi"cant

30 sal}0 sal 0 sal}60 sal 30 sal}60 sal

56)9$3)2 43)4$8)9 56)9$3)2

43)4$8)9 24)9$2)7 24)9$2)7

2)85 3)98 15)29

0 fresh}0 sal 30 fresh}30 sal 60 fresh}60 sal

55)8$8)4 62)6$13)9 36)3$8)4

43)4$8)9 56)9$3)2 24)9$2)7

2)03 0)80 2)58


30 sal}0 fresh

56)9$3)2

55)8$8)4

0)24

Non-signi"cant

Signi"cant Signi"cant Signi"cant

*Fresh, fresh water; sal, saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively; SD, standard deviation.

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G . O R O N E¹ A ¸.

Table 4 The pear yields for the 1995 harvest and 95% signi5cance level implementing one-tailed 9t:-test analysis for assessing the di4erences between the treatments Treatments*

Yield $SD*, Mg ha!1

Yield $SD*, Mg ha!1

Calculated &t'

Non-signixcantand signixcant diwerences at t0)95(6)"1)94

0 fresh}60 fresh 30 fresh}0 fresh 30 fresh}60 fresh 0 sal}60 sal 30 sal}0 sal

55)2$8)1 68)4$7)1 68)4$7)1 33)4$2)2 57)2$7)3

38)5$6)3 55)2$8)1 38)5$6)3 30)2$12)4 33)4$2)2

3)25 2)45 6)30 0)51 6)24

Signi"cant Signi"cant Signi"cant Non-signi"cant Signi"cant

0 fresh}0 sal 30 sal}60 sal 30 fresh}30 sal 60 fresh}60 sal 30 sal}0 fresh

55)2$8)1 57)2$7)3 68)4$7)1 38)5$6)3 57)2$7)3

33)4$2)2 30)2$12)4 57)2$7)3 30)2$12)4 55)2$8)1

5)19 3)75 2)20 1)19 0)37

Signi"cant Signi"cant Signi"cant Non-signi"cant Non-signi"cant

*Fresh, fresh water; sal, saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively; SD, standard deviation.

3.4.2. Soluble solids content Similarly, no signi"cant di!erences could be detected for the soluble solids expressed by the sugar content in the fruits (Tables 6}9). This holds both at the time of harvest and after a 5 month storage period. 3.4.3. ¹itratable acidity A higher level of titratable acidity (TA) content can be identi"ed for all saline water treatments (Tables 6}9). That "nding persists after a 5 month storage. The highest TA content was encountered in the saline water application under the SDI treatment at the depths of 30 and 60 cm.

3.4.4. Core-ush The core#ush analysis conducted only for the 1995 harvest emphasizes the advantage of saline water use (Tables 8 and 9). A relatively high core#ush percentage can be identi"ed for tap water application and a signi"cantly low one for the saline water treatments. 3.4.5. Healthiness The healthiness analysis refers to disease free and overall fruit quality. Similar, to the coreflush parameter, more healthy fruits, in terms of disease free and overall quality, were obtained under the saline water application (Tables 8 and 9). The di!erence

Table 5 Mean soil moisture content and soil salinity given by the electrical conductivity in dS m!1 in the root zone for two water qualities subject to emitter location (120 samples soil samples were taken 3 times during active growing period at 0, 20 and 40 cm radially from the lateral on both sides near emitter and at 0+10, 20+30, 60+70 and 90+100 cm depths) Mean soil moisture content$SD*, %v/v Water quality

Year

Fresh water irrigation Saline water irrigation

Mean soil electrical conductivity$SD*, dS m!1

DI*

SDI30*

SDI60*

DI*

SDI30*

SDI60*

1994 1995 1996

17)2$1)2 15)1$1)3 11)6$0)7

20)2$0)8 15)1$0)9 11)6$0)7

16)8$1)1 13)7$1)0 9)7$0)8

1)4$0)2 3)6$0)5 3)8$0)6

1)8$0)3 4)3$0)5 4)2$0)4

2)0$0)2 0)5$0)4 4)5$0)5

1994 1995 1996

19)0$1)3 19)0$1)2 15)5$0)8

20)2$0)9 19)1$0)7 15)0$0)6

18)9$1)2 17)5$0)6 14)0$0)8

6)1$0)9 8)0$1)2 7)0$1)1

4)8$0)8 7)2$0)8 8)0$1)0

6)4$0)7 8)3$1)0 8)2$1)2

*DI, SDI30 and SDI60, surface drip irrigation, subsurface drip irrigation at 30 and 60 cm depths, respectively; SD, standard deviation.

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Table 6 Pear quality criteria of the 1994 year harvest (three replications)* Water and emitter depth, cm**

Harvest, 28 July 1994

Removal after storage, 19 December 1994

Firmness, N

Soluble solids content, %

Titratable acidity, %

Firmness, N



Tap}0 Tap}30 Tap}60

54)2 60)4 59)2

14)4 13)8 14)5

0)28 0)25 0)30

27)1 24)5 29)2

15)5 15)2 15)4

0)17 0)18 0)21

Sal}0 Sal}30 Sal}60

62)5 61)4 67)2

14)1 14)7 14)7

0)30 0)36 0)36

30)6 32)2 33)1

15)1 15)3 15)7

0)23 0)22 0)24

*Results with same letter (in column) are not signi"cantly di!erent at 5% level according to Duncan multi-range test. -Tap, irrigation with tap water; Sal, irrigation with saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively.

between the tap and saline water is signi"cant (according to Duncan multi-range test) where the 30 cm deep SDI treatment was the superior one.

4. Conclusions Field experiments were conducted in order to con"rm the hypothesis that saline water application under subsurface drip irrigation (SDI) is advantageous in comparison to conventional surface drip irrigation. The results obtained in the study con"rm the assumption that saline water application has a great potential in irrigation, primarily in regard to the agricultural products quality. Saline water application can signi"cantly improve the fruit quality. When shifting from tap to saline water

application it is recommended, in order to minimize yield losses, to use SDI systems. Saline water application under subsurface drip irrigation will provide the most favourable conditions for plant development, subject to soil characteristics and environmental factors. Under SDI, the salts that are contained in the irrigation water and in the soil will be shifted to the periphery of the irrigated root zone domain, including towards the soil surface. Extra precautions are required in order to prevent excessive salts accumulation close to the soil surface during SDI saline water application. That can be maintained by seasonal leaching and irrigation during precipitation. Furthermore, SDI o!ers speci"c advantages like decreased demand due to minimizing evaporation and runo!, better weed control and convenient agricultural machinery manoeuvre. Major considerations will be

Table 7 Pear quality criteria of the 1995 year harvest (three replications)* Water and emitter depth, cmR *


Removal after storage, 1January, 1996

Firmness, N



Firmness, N



Tap}0 Tap}30 Tap}60

55)2 59)9 56)2

14)6 14)0 14)0

0)32 0)34 0)33

37)0 35)7 37)9

14)9 15)1 14)8

0)13 0)18 0)14

Sal}0 Sal}30 Sal}60

54)6 52)7 54)3

14)5 14)9 15)4

0)45 0)51 0)44

39)4 35)0 41)7

14)8 15)5 15)6

0)24 0)22 0)20

*Results with same letter (in column) are not signi"cantly di!erent at 5% level according to Duncan multi-range test. RTap, irrigation with tap water; Sal, irrigation with saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively.

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G . O R O N E¹ A ¸.

Table 8 Removal criteria for the pears 1995 harvest (three replications)* Water and emitter depth, cmR

Removal after storage: 7 days shelf time, 7 January 1996

Removal after storage: 7 days shelf time, 7 January 1996

Firmness, N



Firmness, N



Tap}0 Tap}30 Tap}60

25)8 24)5 27)5

14)6 15)3 14)2

0)16 0)14 0)15

26)7 6)7 49)3

76)7 93)3 96)7

23)3 6)7 3)3

Sal}0 Sal}30 Sal}60

26)3 25)1 27)1

14)7 14)6 14)7

0)21 0)18 0)21

12)3 13)3 9)0

31)7 26)7 43)3

68)3 73)3 56)7

*Results with same letter (in column) are not signi"cantly di!erent at 5% level according to Duncan multi-range test. RTap, irrigation with tap water; Sal, irrigation with saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively.

Table 9 Pear quality criteria of 1996 year harvest (15 fruits per sample)* Water and emitter depth, cmR *


Removal after storage, December 1996

Firmness, N



Firmness, N



Tap}0 Tap}30 Tap}60

44)6 45)4 39)6

14)0 14)5 14)2

0)13 0)06 0)18

16)9 16)1 17)3

15)0 14)6 15)1

0)17 0)17 0)17

Sal}0 Sal}30 Sal}60

38)8 43)0 45)4

13)9 15)4 15)4

0)16 0)20 0)18

19)4 17)3 15)7

14)6 15)4 15)6

0)16 0)19 0)18

*Results with same letter (in column) are not signi"cantly di!erent at 5% level according to Duncan multi-range test. RTap, irrigation with tap water; and Sal, irrigation with saline water; 0, surface drip irrigation; 30, 60, subsurface drip irrigation at 30 and 60 cm depths, respectively.

adequate lateral location and depths. Larger scale demonstrative experiments and "eld monitoring in commercial orchards are required in order to strengthen these "ndings. Acknowledgements The study was partially supported by RASHI Foundation project No. 2438 on &&Development of subsurface porous emitters for improved irrigation management'' and BARD research fund No. IS2552-95 on &&Optimization of secondary wastewater reuse to minimize environmental risks''. The authors appreciate the contributive comments and suggestions made by the editors and anonymous referees.

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247

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