effect of irrigation methods, management and salinity of irrigation water on tomato yield, soil...
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Irrig Sci (2008) 26:313–323
DOI 10.1007/s00271-007-0095-7ORIGINAL PAPER
EVect of irrigation methods, management and salinity of irrigation water on tomato yield, soil moisture and salinity distribution
N. M. Malash · T. J. Flowers · R. Ragab
Received: 25 March 2007 / Accepted: 1 October 2007 / Published online: 17 October 2007© Springer-Verlag 2007
Abstract The increasing demand for irrigation water tosecure food for growing populations with limited watersupply suggests re-thinking the use of non-conventionalwater resources. The latter includes saline drainage water,brackish groundwater and treated waste water. The eVectsof using saline drainage water (electrical conductivity of4.2–4.8 dS m¡1) to irrigate Weld-grown tomato (Lycopersiconesculentum Mill cv Floradade) using drip and furrowirrigation systems were evaluated, together with the distri-bution of soil moisture and salt. The saline water was eitherdiluted to diVerent salinity levels using fresh water(blended) or used cyclically with fresh water. The results oftwo seasons of study (2001 and 2002) showed that increas-ing salinity resulted in decreased leaf area index, plant dryweight, fruit total yield and individual fruit weight. In allcases, the growth parameters and yield as well as the wateruse eYciency were greater for drip irrigated tomato plantsthan furrow-irrigated plants. However, furrow irrigation
produced higher individual fruit weight. The electrical con-ductivity of the soil solution (extracted 48 h after irrigation)showed greater Xuctuations when cyclic water managementwas used compared to those plots irrigated with blendedwater. In both drip and furrow irrigation, measurements ofsoil moisture one day after irrigation, showed that soilmoisture was higher at the top 20 cm layer and at the loca-tion of the irrigation water source; soil moisture was at aminimum in the root zone (20–40 cm layer), but showed agradual increase at 40–60 and 60–90 cm and was stable at90–120 cm depth. Soil water content decreased graduallyas the distance from the irrigation water source increased.In addition, a few days after irrigation, the soil moisturecontent decreased, but the deWcit was most pronounced inthe surface layer. Soil salinity at the irrigation source waslower at a depth of 15 cm (surface layer) than that at 30 and60 cm, and was minimal in deeper layers (i.e. 90 cm).Salinity increased as the distance from the irrigation sourceincreased particularly in the surface layer. The resultsindicated that the salinity followed the water front. Weconcluded that the careful and eYcient management of irri-gation with saline water can leave the groundwater salinitylevels unaVected and recommended the use of drip irriga-tion as the fruit yield per unit of water used was on averageone-third higher than when using furrow irrigation.
Introduction
The continuous increase in the earth’s population requiresincreasing quantities of water for domestic, industrial andagricultural needs. The progressive requirement for morewater to irrigate crops for food when water resources arelimited has lead to reuse and recycling of the availablewater in agriculture (Bouwer 1994; Ragab 1997, 2005). In
Communicated by S. Raine.
N. M. MalashDepartment of Horticulture, MenoWya University, Shibin El Kom, Egypte-mail: [email protected]
T. J. FlowersPlant Physiology, School of Life Science, University of Sussex, John Maynard Smith Building, Falmer, Brighton, East Sussex BN1 9QG, UKe-mail: [email protected]
R. Ragab (&)Head of Water, Soil and Landscape, Center for Ecology and Hydrology, Wallingford OX10 8BB, UKe-mail: [email protected]
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many regions of the world, Weld drainage water is alreadyused successfully for irrigation even when the water issaline (Grattan et al. 1994). Irrigation with saline water hasbecome necessary not only in parts of the world with lim-ited supplies of good quality water but also in areas aVectedby shallow ground water where the main purpose is toreduce the depth of the water table.
The successful reuse of low-quality water requires theselection of salt tolerant crops, the application of a suitablewater management strategy and the choice of the mostappropriate irrigation system; water management, irrigationsystem, soil type and salinity distribution, all aVect cropproductivity. The irrigation water can be used as a mixtureof saline water with fresh water (blending or mixing) orsaline water can be applied in cycles with fresh water. Theuse of saline drainage water for irrigation has an environ-mental advantage as it reduces the fresh water requirementfor salt-tolerant crops and decreases the volume of drainagewater requiring disposal or treatment.
The objective of the work reported here was to comparedrip irrigation with conventional furrow irrigation (which isa common practice in Egypt where the experiment was con-ducted) in terms of: (1) plant production and water useeYciency, (2) moisture and salinity distribution in the soilproWle and within the root zone, and (3) eVects on the watertable level and its salinity. Both irrigation methods (dripand furrow) were used to irrigate tomato plants with eitherfresh or saline drainage water applied by one of two watermanagement strategies; either the fresh and saline waterwere blended or they were applied cyclically (blended orcyclic treatments).
Materials and methods
The experiments were conducted in Welds of the Agricul-tural Experimental Station of the Faculty of Agriculture ofMenouWya University in Shibin El-Kom, Egypt (latitude30.5 North and longitude 31.3 East). The average tempera-tures in the area during the growing season (5 months) were30.6°C as a maximum and 16.0°C as a minimum (averageof 3 years; 2000, 2001 and 2002); there was no rainfall dur-ing the period over which the experiments were conducted.
The soil at the experimental site was a clay loam where theclay content increased from 31% at the top 30 cm layer to40% at a depth between 150 and 180 cm. Over the samerange of depth, the electrical conductivity of saturatedpastes ranged between 0.28 and 0.32 dS m¡1 and the pHincreased from 7.1 in the top 30 cm layer to 8.1 at 150–180 cm depth. Exchangeable Na+ increased from 0.7 mmolper 100 g soil to 21.1 mmol per 100 g over the same depthrange.
Seeds of tomato (Lycopersicon esculentum Mill. cvFloradade) were sown on 11 January in the 2001 and 2002seasons, in seed-beds in a plastic house (to protect seed-lings from cold weather). Floradade is semi-determinateand grown in Egypt in the open Welds as bush variety, with-out training. After hardening, seedlings were transplantedon 10 and 16 March 2001 and 2002, respectively, to Weldplots consisting of Wve rows 6 m long and 1.2 m wide.Transplants were set at 300 mm apart. Each plot area was36 m2 and the distance between any two adjacent plots was1.5 m. Cultural practices such as pest control, harrowingand fertilization were carried out when needed followingthe guidelines of the Ministry of Agriculture in Egypt. Therates of fertilizer application per hectare were: 285 kg N,142 kg P2O5 and 238 kg K2O.
Two irrigation methods (i.e. drip and furrow) were used.The drip irrigation system was of similar design to that usedin Welds by commercial growers in Egypt (using tubes with16 mm internal diameter, with drippers delivering 4 L/h set300 mm apart). For the furrow system, the irrigation waterwas delivered to furrows in the plots by tubes (PVC, 16 mminternal diameter). The irrigation water for both systemscame from three large storage tanks. One was Wlled withsaline drainage water (4.2–4.8 dS m¡1), the second withfresh water (0.55 dS m¡1) and the third was used for mix-ing.
Two water management strategies were used: blended orcyclic. Either saline and fresh water were mixed (blendedtreatment) or fresh and saline water was applied alterna-tively (cyclic treatment).The seasonal average EC of theblended water was 3.0 dS m¡1 (Table 1).
The fresh water originated from a well (about 90 m deepand with water similar to that of the river Nile in the area),while the saline water was collected from drains that
Table 1 Salinity ratio, water management and salinity of irrigation water
Treatment Blended Cyclic Salinity of irrigation water (seasonal average)(dS m¡1)
1 100% fresh All irrigations with fresh water 0.55
2 40% fresh and 60% saline
40% of irrigations with fresh water and 60% with saline water
3.00
3 100% saline All irrigations with saline water 4.50
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Irrig Sci (2008) 26:313–323 315
received excess water from neighbouring Welds withsodium chloride added to raise the EC to the required value.
A split–split plot design with three replicates was used.The layout of the plots and the allocation of treatments areshown in Fig. 1. The irrigation systems were assigned tothe main plot, water management strategies to sub-plotsand fresh and saline water ratios to sub–sub plots (36 m2).The experimental design was carried out according to themethod described by Snedecor (1956). The data were sub-jected to analysis of variance and the signiWcance of diVer-ences between treatments was determined by leastsigniWcant diVerence (Steel and Torrie 1981).
Before the treatments were initiated all plants receivedfresh water. Once the plants became well established(40 days after transplanting) the treatments were applied.One replicate of each treatment was equipped with theUPVC tubes (175 cm long, 3.7 cm width and 3.7 mm thick)of a neutron probe (CPN, 50 mCi, see also Fig. 2). Three orfour tubes were inserted in the soil at intervals of 30 cm, (in2001), or 10 cm, (in 2002) from the irrigation source forestimating soil moisture content vertically and horizontally.The amounts and dates of irrigation were determined in thelight of such measurements. Irrigation occurred when theavailable soil moisture (ASM) reached 70 § 3%, at 60 cmdepth and within 10 cm from the plants, and suYcientwater was added to return the soil moisture to Weld capac-ity. Irrigation was performed on diVerent days for high and
low EC. The diVerent irrigation treatments started in themiddle and end of April in 2001 and 2002, respectively,and continued to the end of the growing season in middle ofJuly in both years. The plants were located at 0 and 30 cmfrom the irrigation source in drip and furrow irrigation,respectively.
Soil salinity (as conductivity of the soil solution) wasmeasured by using salinity sensors (Soil Moisture Equip-ment Corp., Cat No. 5000-A) and a salinity bridge (SoilMoisture Equipment Corp., Cat. No. 5500). Salinity sen-sors were inserted in the soil at depths of 15, 30, 60 or90 cm and horizontally at 0, 10, 20 or 30 cm intervals fromwater source in 2002 (Fig. 2). Measurements were carriedout periodically before and after irrigation.
Soil solution was collected 48 h after each irrigationusing ceramic cups (inserted in the root zone at depthsdepending on plant growth stage: i.e. at 15 cm during vege-tative growth and early Xowering, 20 cm at full Xoweringand early fruiting and 30 cm at fruit development and rip-ening) and the electrical conductivity was determined.
Plant samples were taken at diVerent growth stages: at60, 75 and 90 days after transplanting in the 2001 seasonand at 60, 70, 80 and 90 days in the 2002 season. Each sam-ple consisted of three plants picked from outer rows of eachplot (leaving the three inner rows for yield determination).
Leaf area index (LAI) was calculated as: total plant leafarea/ground area occupied by plant [i.e. 1.20 (row
Fig. 1 An experiment layout (one replicate) showing tanks of fresh water (FW), saline water (SW) and for mixing waters (Mix)
MixSW
Rows
Electric pump
Driplines
Valves
Main irrigation line
FW
Plots
Furrowlines
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316 Irrig Sci (2008) 26:313–323
width) £ 0.30 m (planting distance)]. Fresh and dry weightof plants was determined. Dry weights were measured48 hours after placing fresh samples in an oven at 105°C(it was previously established that after 48 h, the sampleshad reached constant weight). Fruits were harvested two tothree times per week and at the end of the harvesting sea-son, total fruit yield, total fruit number and average fruitweight were determined. Fruit total soluble solids (TSS)content (using an Abbé hand-held refractometer) were alsodetermined in four fruit samples (each contained Wve fruitsfrom each treatment) taken throughout the harvestingseason.
Piezometers were inserted at 3 m depth in eight diVerentsites around the experimental area (four sites in the drip-irrigated area and four in the furrow-irrigated area, includ-ing most fresh and saline water treatments). The water tablelevel was periodically measured using a sounder plus glass-Wbre 5 m tape, with a metal hook for the sounding device,
Eijkelkamp Agrisearch Equipment, The Netherlands). Oneach occasion, samples were taken to measure the electricalconductivity (EC) of the ground water.
Results
Plant growth
Leaf area index
It is clear from Table 2, that the LAI was at its highest whenplants were irrigated using the drip system and fresh water,in both seasons. Regardless of the water management strat-egy and saline ratios used, drip irrigation always producedhigher values of LAI than furrow irrigation. Using thecyclic strategy reduced the LAI in comparison with theblended strategy except for drip irrigation in 2002.
Fig. 2 Instruments distribution on rows of diVerent treatments
1.2 m
1.2 m
6 m
Instruments distribution on a row irrigated by drip (21 plants on a row)-------------------------------------------------------------------------------------------------------
0.3m
0.3 m
6 m
Piezometer
Tubes of neutron probe
Irrigation line drippers
Ceramic cup
Piezometer
Tubes of neutron probe
Salinity sensors at 10 cm intervals from irrigation source and different
depths
Ceramic cup
0.3 m
Salinity sensors at 10 cm intervals from irrigation
source and different depths
Irrigation water
Furrow
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Irrig Sci (2008) 26:313–323 317
The reduction in LAI caused by the highest saline ratio wasabout 30% (average of the two seasons) when saline waterwas applied by drip and 42% using furrow irrigation whencompared to the treatment that received fresh water by drip.Using the ratio of 40% FW/60% SW in irrigation decreasedLAI by up to 28% when applied in the cyclic system however;the reduction was only 22% when the water was blended.
Plant dry weight
Drip irrigation and fresh water produced the highest plantdry weight (Table 2). In general, drip irrigation always pro-duced the highest values, regardless of management strat-egy or salinity ratio and high salinity reduced plant dryweight. However, it is worth noting that dry weights ofplants receiving 40% FW/60% SW blended water (particu-larly in 2001) were not signiWcantly diVerent from thosereceiving 100% fresh water. This observation suggests thata blended strategy could alleviate the hazard of salinity par-ticularly at intermediate levels. The blended strategyenhanced plant weight more than the cyclic strategy evenwhen plants were irrigated with the same level of salinity.
Yield and yield components
Total yield/plant
The data in Table 3 shows that fruit yield decreased gradu-ally with increasing salinity ratio of irrigation water. Thereduction in fruit yield, averaged across the two seasons,caused by using the ratio 40% FW/60% SW (regardless ofwater management system) was 14% and by using 100%SW was 32% when drip irrigation was used. Counterpartvalues for furrow irrigation were 26.5 and 39%, respec-tively. The reduction in yield was more pronounced (thediVerence was signiWcant) when 40% FW/60% SW ratio
was applied cyclically than when blended water was used(reduction was not signiWcant). In all cases, using drip irri-gation gave higher yields than furrow irrigation.
Average fruit weight
Using 100% saline water in irrigation signiWcantly reducedthe average weight of a fruit compared to those producedwith fresh water. Using 40% FW/60% SW ratio alsoreduced average fruit weight compared to those producedby 100% fresh water, but diVerences were signiWcant onlywhen this saline ratio was applied cyclically and particu-larly in 2001 (Table 3). In all cases, furrow irrigation pro-duced bigger fruit (higher fruit weight) than did dripirrigation. Although the reduction in fruit yield as a resultof using saline water (100%SW) in irrigation was 40%, thereduction in average fruit weight under such condition wasonly 8%. This means that fruit number, the second mostimportant component of fruit yield, was also reduced bysalinity and the reduction in fruit number was more pro-nounced than in fruit weight.
Fruit total soluble solids (TSS) content
An increasing ratio of saline water in the irrigation causedan increase in fruit TSS content (Table 3). It was alsoobserved that fruits harvested from plants furrow-irrigatedwith saline water, had a greater TSS than those counterpartsthat were drip irrigated. Using the blended water manage-ment strategy (regardless of irrigation method) producedslightly higher TSS content than with cyclic management.
Water use eYciency
Water use eYciency (WUE) estimated as the fruit yield perunit of water supplied in 2001, was about three times
Table 2 The eVect of irrigation systems, water management strategy and salinity on leaf area index and plant dry weight of tomato
Data from harvests 90 days after transplanting (50 days after treatment initiation) in 2001 and 2002
FW Fresh water, SW saline water, C cyclic, B blended
Irrigation systems
Fresh and saline water ratios and management
Leaf area index (m2/m2 ) Plant dry weight g/plant
2001 2002 2001 2002
Drip 100% FW 4.74 4.75 317 321
40% FW/60% SW (C) 3.50 3.71 284 283
40% FW/60% SW (B) 3.79 3.83 303 298
100% SW 3.32 3.37 273 268
Furrow 100% FW 3.82 3.92 284 288
40% FW/60% SW (C) 3.17 3.23 254 250
40% FW/60% SW (B) 3.61 3.59 275 269
100% SW 2.78 2.81 227 228
L.S.D at P = 0.05 0.14 0.19 28.3 21.3
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greater for drip irrigated plots than for those irrigatedthrough furrows (Table 4). The 2002 data showed a similarpattern. The management strategy had little eVect on WUEunder furrow irrigation, but was, on average, 30% greaterwhen plots were drip irrigated with blended water ratherthan cyclic saline and fresh water. Averaged across salini-ties and management strategies, furrow irrigation used 2.6times more water than drip irrigation (data not presented).
Salinity of soil solution
The electrical conductivity of the soil solution increasedsigniWcantly with increasing salinity of the irrigation water(Fig. 3). In plots irrigated using the cyclic managementstrategy there was, as expected, a Xuctuating conductivity,which followed the application of saline or fresh water insaline treatments. However, following the application offresh water, the salinity in this treatment did not decrease tothat of the treatments that received fresh water in all irriga-tions (100% FW). In blended-management plots, soil solu-tion salinity generally increased with time and the salinityof the furrow-irrigated plots was marginally greater thanthat of the same salinity in drip treatments (Fig. 3).
Soil moisture and salinity distribution in the soil proWle as aVected by irrigation methods
After the drip irrigation (Fig. 4, left) soil moisture contentwas found to be the highest in the soil top 20 cm layer at theirrigation source (0 cm from irrigation source). Moisture at
Table 3 The eVect of irrigation systems, water management strategy and fresh and saline water ratios on tomato fruit yield and its components
FW Fresh water, SW saline water, C cyclic, B blended
Irrigation systems Fresh and saline water ratios and management
2001 2002
Total yield/plant (kg)
Average fruit wt. (g)
Fruit TSS (%)
Total yield/plant (kg)
Average fruit wt. (g)
Drip 100% FW 2.99 107.8 4.7 3.19 100.7
40% FW/60% SW (C) 2.50 99.2 4.9 2.61 99.2
40% FW/60% SW (B) 2.80 104.5 5.1 2.75 99.4
100% SW 2.09 97.1 5.3 2.09 93.1
Furrow 100% FW 2.70 116.0 4.9 2.69 105.3
40% FW/60% SW (C) 2.10 99.6 5.0 2.07 97.7
40% FW/60% SW (B) 2.48 111.4 5.3 2.42 102.5
100% SW 1.87 98.0 5.5 1.90 92.9
L.S.D at P = 0.05 0.26 5.4 – 0.41 4.4
Table 4 EVect of irrigation methods, water management strategiesand fresh and saline water ratios on water use eYciency in 2001 season
FW Fresh water, SW saline water, C cyclic, B blended
Fresh and saline water ratios and management
Water use eYciency (kg/m3)
Drip Furrow
100% FW 49.1 19.3
40% FW/60%SW (C) 60.6 17.8
40% FW/60% SW (B) 79.4 22.2
100% SW 60.4 19.6
L.S.D. at P = 0.05 4.75 4.75
Fig. 3 The eVects of irrigation method, i.e. furrow (left) and drip (right), water management strategy {cyclic (C) or blended (B)} and salinity of the irrigation water on changes in soil solution salinity (dS m¡1) over time in the year 2001. Measurements at 0 times were taken at 5 and 2 days after treatments initiation in drip and furrow irrigation methods, respectively
0
1
Furrow Drip
100% FW 40% FW/60% SW (C) 100% SW 40% FW/60% SW (B)
2
3
4
5
6
7
0 7 14 21 28 36 43 50 57 64
Time ( days after treatment initiation)
mSd ni noitulos lios fo ytinila
S1-
8
0
1
2
3
4
5
6
7
8
0 7 14 21 28 36 43 50 57 64 71 78
Time (days after treatments initiation)
mSd ni noitulos lios fo ytinilaS1-
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a soil depth of 20–40 cm showed the lowest content at alldistances from the irrigation source. Moisture content grad-ually increased with deeper layers (40–60, 60–90 and 90–120 cm). Before irrigation soil moisture content of the sur-face layer (0–20 cm) dramatically decreased particularly at0 and 30 cm from the irrigation source (data not shown).The greatest changes in soil moisture content (Fig. 4, left)were observed between 0 and 40 cm, particularly at the siteof irrigation. Moisture at deeper layers was mostly stable.
Moisture in the soil proWle of plots receiving water byfurrow irrigation (Fig. 4, right) showed a similar pattern todrip irrigation (Fig. 4, left) but the water content was a littlehigher until 40–60 cm below the surface. This was also thecase at 0 and 30 cm horizontal locations from the irrigationwater source. Before irrigation (data not shown) soil mois-ture decreased horizontally away from the irrigation sourceparticularly to a depth of 0–40 cm. In general moisture con-tent in deeper layers was stable in all cases. In all casesmoisture at 30 cm distance was lower than that at 0, 10 or20 cm from irrigation source.
In plots irrigated by drip, soil salinity was highest in thesurface layer (top 15 cm) at 30 cm distance from the watersource (Fig. 5, left). Soil salinity in this surface layer reducedgradually as the sampling point was closer to the dripper (20,10, 0 cm). At 30 cm depth, 10 cm from the irrigation source,salinity tended to increase again (Fig. 5, left). In deeperlayers salinity decreased to a minimum at 90 cm depth wheresalinity was almost stable horizontally. But, salinity increasedas distance from the irrigation source increased.
Before irrigation, salinity was higher, than after irriga-tion, at all monitored points, but showed the same pattern ofdistribution as after irrigation (data not shown). Salinity atthe irrigation source (the location of plant in drip irrigation)
and down to a depth of 15 cm was the lowest, but tended toincrease till depth of 30 cm.
In furrow-irrigated plots (Fig. 5, right), the salinity dis-tribution showed a diVerent pattern from that observed indrip irrigation. Salinity was highest in the surface layer(top15 cm), and decreased gradually with soil depth. Also,salinity increased as distance from the irrigation sourceincreased, up to 20 cm where the highest values wererecorded. Beyond 30 cm distance, (the position of the plantin furrow irrigation) salinity reduced slightly.
As a comparison between the two irrigation methods,salinity at 30 cm from irrigation source in drip irrigatedplots (at the edge of the wetted area) and at 20 cm in furrowirrigated plots (at the edge of the row) was higher than theother locations from irrigation source (Fig. 5). In generalsalts followed the water front.
Water table level and salinity
It is clear from Fig. 6 (top) that the water table depth variedfrom location to location. There were places where thewater table was shallow and others where the water tablealways deep. Variation in water table depth was probablydue to variation in topography or to the variation in thedepth of the impermeable layer.
Although there was a tendency for the depth of the watertable to increase with time, there was no rapid Xuctuation inits value, which was fairly stable (Fig. 6, upper), suggestingthat irrigation in this experiment had little inXuence on thelevel of the water table. The slow increase in the depth ofthe water table was probably a consequence of irrigation byneighbouring farmers who started planting their main sum-mer crop (cotton) at the beginning of March, when the
Fig. 4 Vertical and horizontal (at 0, 10, 20 and 30 cm from irri-gation source) moisture (%) dis-tribution in soil proWle after irrigation with saline water using the drip (left) or furrow (right) systems
360-20 20-40 40-60 60-90 90-120
38
40
42
44
46
egat necre p er utsiom lioS
48
50
Soil depth (cm)
36
38
40
42
44
46
48
50
0- 20- 60- 90-20 40 40-60 90 120
Soil depth (cm)
egatnecrep erutsiom lio
S
0 cm10 cm20 cm30 cm
Fig. 5 Vertical and horizontal (at 0, 10, 20 and 30 cm from irri-gation source) salinity (dS m¡1) distribution in soil proWle after irrigation with saline water using the drip (left) or furrow (right) systems
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
15 30 60 90
Soil depth (cm)
mSd ni ytinilas lio
S1-
4.
0.00.51.01.52.02.53.03.54.0
15 30 60 90
Soil depth (cm)
mSd niytinil as l io S1-
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320 Irrig Sci (2008) 26:313–323
regional irrigation scheme involves 7-day cycles (withwater available for 7 days and then unavailable for 7 days).From the 18th of April each year, and after establishment ofthe crop, usually irrigation by farmers becomes less fre-quent, i.e. 5 days on and 10 days oV.
The EC of the water table was also unaVected by any ofthe treatments of this experiment although salinity was pos-itively related (r = 0.923) with water table depth (Fig. 6,bottom). In other words the salinity of the water tabledecreased when the water table level rose as a result ofincreasing amount of drainage water coming from neigh-boring Welds and vice versa.
Discussion
Traditionally, irrigation was eVected by Xooding Welds withwater, but such methods allow signiWcant losses of water todrainage and evaporation. The use of drippers reduces theselosses but attracts additional costs for equipment. Conse-quently, farmers require good reasons if they are to invest innew technologies. Where water is in short supply, there maybe clear advantages in using a drip system in preference to amore traditional method of water application, especially fora farmer who has to pay for water. These advantages may begreater if saline water can or has to be used. Saline water
may be cheaper than fresh water and reducing water use byuse of a drip system should reduce the quantity of waterrequired for leaching. However, if drip systems are to beused, the farmer must be convinced that any additional costswould be covered by improvements in yield.
There have been previous investigations into the eVectsof salinity on the performance of tomato, with experimentsundertaken in the Weld soils and in lysimeters (Table 5). Allof these investigations (except Hanson and May 2004, ref.9, Table 5 who did not report plant data) showed that thesalinity depressed the plant performance, whether estimatedas leaf area index (this paper, Romero-Aranda et al. 2001,ref. 2; Maggio et al. 2004, ref. 7), fruit number or fruit size(this paper (0); Elamin and Al-wehaibi 2005, ref. 3; delAmor et al. 2001, ref. 6; Maggio et al. 2004, ref. 7), yield(this paper); del Amor et al. 2001, ref.6; Maggio et al.2004, ref.7; Abuawwad and Hill 1991, ref.8; Naresh et al.1993, ref. 10), or dry mass (this paper ; Romero-Arandaet al. 2001, ref.2; Elamin and Al-wehaibi 2005, ref.3; Mag-gio et al. 2004, ref.7). Where both drip and furrow systemshave been compared using saline water, plants under dripoutperform those that are furrow irrigated (this paper; Heb-bar et al. 2004, ref.1; Maggio et al. 2004, ref.7).
Very few papers reported comparisons between cyclicand blended water: In our case (this paper), alternatingapplication of saline water with fresh water gave lesstomato production than did mixing both waters together,perhaps due to the richness of the saline water in nutrientsas this water was originated from drainage of over irrigatedneighbouring commercial Welds. The latter usually receivea great deal of fertilizers and some of these fertilizers getwashed out to drains by over irrigation. Mixing this waterwith fresh water and continuously irrigating with it, wouldlead to a continuous supply of nutrients to the plants. Overthe season, the amount of nutrients received by blendedwater was possibly greater than the cyclic application. Inaddition, the dilution eVect when adding fresh water tosaline water would reduce the impact of salinity stress onplants when compared with cyclic application where salinewater is applied without dilution by fresh water. Usingblended water with moderate saline water seems to givereasonable results. This view is also shared by Dinar et al.(1986, ref.11) who concluded that technical and economicfeasibility of mixing waters of diVerent quality increased asthe EC of saline water decreases. In another comparison(Naresh et al. 1993, ref.10) yields were higher with cyclicsalinity than when blended water was used.
Romero-Aranda et al. (2001) concluded that saline waterreduced water uptake, transpiration/uptake and net CO2 assim-ilation, which in turn reduced the growth and transport ofnutrients into the plants. Generally, a reduction in LAI leads toa reduced light interception and thus reduced dry matter pro-duction (Alarcon et al. 1994; Li and Stanghellini 2001; Kutuk
Fig. 6 Water table depth in cm (top) and its salinity in dS m¡1
(bottom) taken at four locations in furrow irrigated area and measuredthroughout the 2001 season (diVerent symbols represent diVerentlocations)
200
210
220
230
240
250
260
270
280 21/4 26/4 15/5 17/5 27/5 30/5 2/6 20/6 2/7 11/7
Date
Wat
er t
able
dep
th in
cm
Wat
er t
able
sal
init
y in
dSm
-1
1.45
1.5
1.55
1.6
1.65
1.7
1.75
1.8
21/4 26/4 15/5 17/5 27/5 30/5 2/6 20/6 2/7 11/7
Date
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Irrig Sci (2008) 26:313–323 321
et al. 2004). Saline irrigation water, in this study, enhancedfruit TSS content and increased WUE of tomato plants.Reduced water uptake in plants irrigated by saline water led toincreases in solute concentrations (particularly sugars) andhence increased TSS contents. Also, the water use eYciency(WUE), calculated here as the amount of fruit produced perunit of water supplied, increased with increasing salinity.
Using high salinity water for irrigation decreased waterloss from the soil by evapo-transpiration, so a decline insoil water content was minimized under such conditions.When the plots being irrigated with fresh or low salinitywater had reached 70% ASM (the water content for re-irrigation) those plots that received highly saline water stillhad a water content greater than 70% and so were re-irrigated a few days later. So, during the course of a season,a few irrigations were applied to high salinity plots.Consequently, the amount of irrigation water devoted toplots that received the higher salinity treatments was lessthan those at lower salinity and this led to the increases inWUE.
When considering the use of saline water, one shouldkeep in mind the salt tolerance level of the crop. The vari-ety used in this study is moderately tolerant.
Although the cost of a drip system per unit area irrigatedis approximately six times that of a furrow system whencalculated for a single year, the advantage lies with the dripirrigation when costs are calculated for larger areas overlonger period of time (Abouzaid 2002). With such a drip
system, on average, blending water provides a better yieldthan alternating fresh and saline water, especially at moder-ate salinities.
Technically, the use of blended water is a lot easier tomanage by farmers and does not require separate irriga-tion canals as does the cyclic application. However, itdoes require the availability of both waters at the sametime. In areas where fresh water is not always available,farmers might resort to cyclic application where they canirrigate with saline water until the fresh water becomesavailable.
In the absence of sound water and Weld management, useof saline water could have a negative impact on the envi-ronment. Good management would require the selection ofa salt tolerant variety, a good estimation of crop waterrequirements, a good tillage practice and a proper andeYcient drainage system to intercept the saline drainagewater before reaching the groundwater, avoid shallowwater table presence and to convey the saline water to a dis-posal location. In addition, a soil salinity monitoring systemshould be in place. Excessive leaching could also leachnutrients which is not desirable. Leaching is only requiredduring the season if soil salinity approaches the thresholdvalue that would negatively impact on the crop growth. Iffresh water is available, post harvest irrigation or irrigationjust before sowing of the next crop would be beneWcial inleaching the salt accumulated in the soil proWle from theprevious crop.
Table 5 Summarized methods and results of this paper (0) and other related previous reports (from 1 to 11; indicated below)
S¡ = reduced by salinity D = drip optimal D = F i.e. equal in their eVect Blank cell = treatments or measurements that were not done
S+ = increased by salinity F = Furrow optimal Fl = Xood irrigation
C¡ = reduced by cyclic C = cyclic optimal Sums = unaVected upon moderate salinization
B¡ = reduced by blended B = blended optimal Snsr = not signiWcantly reduced
Reference 0 1 2 3 4 5 6 7 8 9 10 11
Experimental site
Field plots � � � � � � � �
Tanks � � �
Irrigation method
Drip � � � � � � � �
Furrow � � � Fl
Management
Cyclic � � �
Blended � � �
Salinity estimated in
Irrigation water � � � � � � � �
Soil �
Soil parameters reported
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322 Irrig Sci (2008) 26:313–323
0, this paper
1, Hebbar et al. (2004)
2, Romero-Aranda et al. (2001)
3, Elamin and Al-wehaibi (2005)
4, Singandhupe et al. (2003)
5, Yadav and Paliwal (1990)
6, del Amor et al. (2001)
7, Maggio et al. (2004)
8, Abuawwad and Hill (1991)
9, Hanson and May (2004)
10, Naresh et al. (1993)
11, Dinar et al. (1986)
Conclusion
The tomato fruit yield per unit of water supplied was onaverage one-third better in drip irrigation than in the furrowirrigation. In addition drip irrigation has resulted in an 11%yield advantage over furrow irrigation. Moreover drip irri-gation maintained ideal water levels in the soil and reducedsalinity in the root zone when compared with the furrowirrigated plots. An added advantage of the use of drip irri-gation was the possibility of using low salinity water withlittle or no reduction in yield, thus saving fresh water fordomestic and industrial uses and for irrigation of salt-sensi-tive crops. The use of blended fresh water with low tomedium saline water led to only a slight reduction in yieldwhen compared to cyclic treatment.
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Moisture content S+D
S+ S+
Salinity S+ S+ S+ S+
Water table D = F D
Plant attributes reported
LAI S¡D
D S¡ S¡
Fruit no. S¡ S¡ S¡ Sums
Fruit size S¡ S¡ S¡ S¡Yield S¡
DD C¡ D D S¡ S¡ S¡ C
S¡B
Fruit TSS S+ C+ S+ S+
Dry weight DS¡
D S¡ Snsr S¡
Reference 0 1 2 3 4 5 6 7 8 9 10 11
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