SALT ACCUMULATION IN THE ROOT ZONES OF TOMATO AND COTTONIRRIGATED WITH PARTIAL ROOT-DRYING TECHNIQUEy

HARUN KAMAN, CEVAT KIRDA, MAHMUT CETIN* AND SEVILAY TOPCU

Cukurova University, Faculty of Agriculture, 01330 Adana, Turkey

ABSTRACT

In this study, soil salinisation was investigated under a newly evolving irrigation practice, called partial root

drying (PRD), which was used for irrigation of tomato and cotton. Under the PRD technique, a reduced amount

of water compared to full plant water requirement was applied to one half of the plant root zone and leaving the

other half dry. The wetting and drying halves of the root zone were alternated in subsequent irrigations.

Greenhouse-grown tomato was drip irrigated, but field-crop cotton was furrow irrigated. Three irrigation

treatments were tested for cotton grown in 2000: (1) FULL irrigation, the control treatment where the plant water

requirement was fully met and water was applied to all sides of the plant root zone, as traditionally practised,

(2) 1PRD and (3) 2PRD where irrigation water applied was reduced by 50% compared to FULL irrigation. The

wetting and drying parts of the root zone were alternated every irrigation under 1PRD, whereas it was alternated

every other irrigation under 2PRD. For tomato, the 2PRD treatment was replaced with conventional deficit

irrigation (DI) which again received 50% less water compared to FULL irrigation, but water was applied to all

sides of the root zone, as practised under FULL irrigation. Soil water status of the plant root zone was

continuously monitored with a neutron water gauge and tensiometers. Two sets of salinity measurements, at the

start of the season and at harvest, were used to assess soil salinity. In addition to crop yield data, soil-salinity

profiles and plant root zone isosalinity maps, constructed at harvest, were used to assess salt accumulation

differences influenced by different irrigation treatments. The results showed that differences in salt accumulation

were limited to only the surface layer of 30 and 20 cm depth for cotton and tomato, respectively, and the soil

salinity at harvest under the PRD effect was 35% higher compared to FULL irrigation for tomato and cotton. The

maximum salt accumulation encountered in the cotton field and greenhouse soil was 1.3 and 7.5 dSm�1,

respectively. Salt accumulation resulting under the PRD effect in the field was in no case higher than salt

tolerance threshold levels of common field crops, including cereals, cotton and the like. Increase of salt content in

the greenhouse soil was independent of the irrigation treatments used, and the accumulation mostly occurred

within surface soil of 20 cm depth. The salt accumulation observed in tomato plots did not reach, in any case,

tomato salt tolerance threshold level. However, the greenhouse soil needs leaching, as regularly practised, for the

following year’s crop. In this respect, the PRD practice and conventional DI do not require additional salt

leaching over what is normally practised under FULL irrigation to sustain soil fertility. Therefore, one can

conclude that the PRD practice should be valued equally with conventional DI for increasing crop water use

efficiency with the least salinisation risk. Copyright # 2006 John Wiley & Sons, Ltd.

key words: deficit irrigation (DI); partial root drying; PRD; salinity map; salt tolerance; crop water use efficiency

Received 21 February 2005; Revised 12 May 2005; Accepted 18 May 2006

IRRIGATION AND DRAINAGE

Irrig. and Drain. 55: 533–544 (2006)

Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ird.276

*Correspondence to: Mahmut Cetin, Cukurova University, Faculty of Agriculture, 01330 Adana, Turkey. E-mail: mcet64@cu.edu.tryAccumulation de sel dans la zone racinaire de la tomate et du cotton irrigues en ‘‘sechage partiel de racine’’.

Copyright # 2006 John Wiley & Sons, Ltd.

RESUME

Ce travail etudie la salinisation du sol sous une technique d’irrigation en pleine evolution appelee ‘sechage partiel

de racine’ (PRD) qui a ete utilisee pour l’irrigation de la tomate et du coton. Avec la methode PRD, une quantite

reduite d’eau par rapport a ce que necessite le plant complet a ete apportee a une moitie de la zone racinaire de la

plante, laissant l’autre moitie seche. Les moities seches et mouillees de la zone racinaire ont ete alternees a chaque

arrosage lors d’irrigations successives. Les tomates cultivees en serre ont ete arrosees au goutte a goutte alors que

les champs de coton ont ete irrigues suivant la technique d’irrigation a la raie. Trois traitements d’irrigation ont ete

testes pour le coton cultive en 2000: (1) PLEINE irrigation, methode traditionnelle qui couvre en totalite les

besoins en eau de la plante et ou l’eau est apportee de tous les cotes de la zone racinaire de la plante; (2) 1PRD et

(3) 2PRD, consistant en une irrigation reduite de 50% par rapport a la PLEINE irrigation. Le mouillage et le

sechage de la zone racinaire ont ete alternes a chaque irrigation sous 1PRD, alors qu’il a ete alterne toutes les deux

irrigations sous 2PRD. Pour la tomate, le traitement 2PRD a ete remplace par l’irrigation deficitaire (DI)

conventionnelle ou, la encore, l’apport en eau a ete egal a 50% de celui de la PLEINE irrigation, mais a ete effectue

de tous les cotes de la zone racinaire, comme ce qui est pratique lors de la PLEINE irrigation. L’etat d’humidite du

sol ou se trouve la zone racinaire a ete mesure tout au long de la saison par des jauges a eau a neutron et des

tensiometres. Deux series de mesures de la salinite ont ete effectuees, une en debut de saison et l’autre au moment

de la recolte, afin d’etablir la salinite du sol. En plus des donnees concernant la production des plants, des profils de

salinite du sol et des cartes d’iso-salinite de la region des racines de la plante, etablis au moment de la recolte, ont

ete utilises pour etablir les differences d’accumulation du sel suivant les differentes techniques d’irrigation. Les

resultats ont montre que les differences dans l’accumulation de sel etaient limitees a la couche de surface sur

respectivement 30 et 20 cm de profondeur pour le coton et la tomate et que la salinite du sol a la recolte suite a la

technique de PRD etait de 35% superieure a celle lors de PLEINE irrigation pour les tomates et le coton. Les

salinites maximales rencontrees dans le sol du champ de coton et dans la serre etaient respectivement de 1.3 et

7.5 dSm�1. L’accumulation du sel resultant de l’utilisation de la technique de PRD dans le sol du champ n’etait en

aucun cas superieure au niveau de tolerance des cereales, coton et autres plantes maraıcheres en general.

L’augmentation de la forte salinite initiale dans le sol de la serre etait independante de la methode d’irrigation

employee, et l’accumulation de sel s’est retrouvee notamment dans la couche superficielle du sol sur 20 cm de

profondeur. L’accumulation de sel observee dans les parcelles de tomates n’a atteint a aucun moment la valeur du

seuil de tolerance au sel de la tomate. Toutefois, il est necessaire d’operer l’habituel lessivage du sol de la serre

pour la saison de production suivante. Par consequent, la pratique de PRD et de DI conventionnelle ne necessite

pas de lessivage supplementaire du sol par rapport a ce qui est normalement pratique pour maintenir la fertilite du

sol. Nous pouvons donc conclure que la technique PRD doit etre evaluee au meme titre que la DI conventionnelle

pour augmenter le rendement de l’utilisation de l’eau par la plante avec un risque de salinisation minimum.

Copyright # 2006 John Wiley & Sons, Ltd.

mots cles: irrigation deficitaire (DI); sechage partiel de racine; PRD; carte de salinite; resistance au sel; reponse (de la plante) a l’eau

INTRODUCTION

Increased demand for domestic and industrial use of water has resulted in a decrease of water allocation for

agricultural use. Increased population necessitates use of not only innovative agronomic practices to increase crop

yields but also use of new irrigation technologies to increase crop water use efficiency. Therefore, advances in

agriculture have aimed at increasing crop production, and in this respect new developments in irrigation

technologies are of great importance.

Water allocation to irrigated agriculture is to decrease in arid and semi-arid regions of high water scarcity. Under

the circumstances described, the so-called deficit irrigation (DI) method of high crop water use efficiency (WUE)

can maintain high crop yields if it is properly used. As pointed out by Kirda et al. (1999), a proper and effective use

of DI requires knowledge of specific crop growth stages during which they are water-stress tolerant, and therefore

irrigation during these stages can either be omitted or reduced. General practice of DI may therefore be difficult

due to limited knowledge or experience of plant growth stages of water-stress tolerance.

Copyright # 2006 John Wiley & Sons, Ltd. Irrig. and Drain. 55: 533–544 (2006)

DOI: 10.1002/ird

534 H. KAMAN ET AL.

The partial root-drying (PRD) irrigation technique where the two halves of plant roots are exposed alternately to

drying and wetting cycles is relatively easy to use, compared to conventional DI. Under the PRD practice, a reduced

amount of irrigation water, similar to deficit irrigation, is applied and significant savings in water use can be

achieved. Available irrigation water supplies are used effectively and high water use efficiency can be attained

(Kang et al., 1998; Chaffey, 2001). Plants with the two halves of their roots under alternating drying and wetting go

through partial drying, which activate root-to-shoot signals for triggering physiological mechanisms to save and

efficiently use water thorough stomatal regulation (Davies and Zhang, 1991). The old practice of alternating furrow

irrigation is essentially similar to PRD practice if wetting and drying are alternated at intervals long enough to

promote root-to-shoot signalling for stomatal control of transpiration, as occurs under the PRD practice. Increase of

abscisic acid (ABA) in xylem elements among many other signalling mechanisms causes closure of stomata and

thereby prevents luxury transpiration (Stoll et al., 2000), with no effect however on photosynthesis (Jones, 1992).

While the reduced transpiration decreases vegetative growth it enhances generative development and thereby

prevents drastic yield reductions.

Decreasing irrigation water requirement through use of new irrigation technologies is of utmost importance in

water-scarce regions. However, sustaining soil fertility is also a great concern in many countries. Among the likely

problems which may degrade soil fertility, soil salinity most commonly develops under mismanaged irrigation

schemes and it may cause permanent loss of soil fertility if timely corrective measures are not taken. Of 7� 109 ha

of global agricultural land, 1.5� 109 ha of land is under cultivation for agricultural production (Masoud, 1981).

Salinity affects nearly 70% of all agricultural lands in over 100 countries, and sadly there is no continent free of soil

salinity problem (Szabolcs, 1989). According to estimates made by FAO and UNESCO, 10 million ha of irrigated

land are abandoned annually as a consequence of soil salinity (IAEA, 1995), and the extent of soil salinity increases

continuously.

This study was taken up to assess salt accumulation in the root zones of tomato and cotton, irrigated with FULL

irrigation where the plant water requirement was fully met, and also with partial root-drying (PRD), a deficit

irrigation practice where the two halves of the plant root zone go through alternate wetting and drying cycles

throughout the season. Conventional deficit irrigation (DI) was also included in the tomato study. The results were

discussed in view of whether the salt accumulation would reach to plant salt tolerance threshold levels.

MATERIALS AND METHODS

The study was conducted in 2000 and 2001 at the research field of Cukurova University, Faculty of Agriculture (368590 N latitude, 358 180 E longitude; 20m altitude). The area had a typical Mediterranean climate, with a cool and

rainy winter and hot and dry summermonths, of annual rainfall of 646.5mm.Mean annual temperaturewas 18.88C,with hottest month of August with 28.18C and the coldest month of January with 9.98C. Mean annual wind speed

and relative humidity were 1.7m s�1 and 66%, respectively.

The experimental work implemented was for furrow-irrigated cotton, and greenhouse grown and drip-irrigated

tomato.

Cotton

The soils of the experimental field were of dark-red brownish colour with medium lime content. The soil profile

contained a high proportion of smectite-type clays with swelling and cracking properties when subjected to wetting

and drying processes, respectively (Ozbek et al., 1974). Based on the soil taxonomy, the experimental soil in the

cotton field was classified as Palexerollic Chromoxerert with heavy-textured clay soil overlaying medium-textured

sandy clay subsoil (Dinc et al., 1995). Soils had medium permeability with high water retention capacity of

120–140mm per 100 cm (Kirda et al., 2004). Soil pH was 7.7–8.0, soil bulk density varied from 1.16 to

1.25 g cm�3, water retention at field capacity, defined at �0.033MPa, was 0.40 cm3 cm�3, and permanent wilting

point at �1.5MPa was 0.26–0.28 cm3 cm�3. The soils of the experimental site had no salinity problem with

saturation extract ECe of 0.16– 0.25 dSm�1.

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IRRIGATION AND SALT ACCUMULATION WITH PARTIAL ROOT-DRYING TECHNIQUE 535

A furrow irrigation method was used for cotton. The spacing between the furrows was 0.8m. A randomized

complete block experiment design with three irrigation treatments (FULL, 1PRD and 2PRD) and three replicates

was used (Table I). The sub-plot size was 40� 6.4m (256m2) with 8-row plants.

A popular cultivar of cotton (Gossypium hirsutum L., cv. Cukurova-1518) was sown on 16 May 2000, with a

seeding drill, adjusted to 3– 4 cm soil depth and 80 cm row spacing, at a seeding rate of 60 kg ha�1. When plants

were fully established and had three to four leaves, thinning was done to 15–20 cm spacing. Fertiliser rates used

were the same as generally practised in the region, and the rates of N, P and K were 160, 50 and 50 kg ha�1,

respectively. Full rates of P and K, and 50 kg ha�1 of N were applied at planting. The remaining Nwas applied at the

late vegetative stage, 55–69 days after sowing (DAS).

Irrigation water used was diverted from the Seyhan irrigation scheme, with an average EC of 0.4 dSm�1.

Irrigation scheduling was based on depletion of plant available water content (PAWC) under the FULL irrigation

plots, which were used as control treatment. When 40% of the PAWC within 90 cm soil depth was depleted,

irrigation was resumed and the PAWC brought up to 100%, following each irrigation. The irrigation season

continued until the time when 10% of the bolls fully opened, as generally practised in the region (Karaata, 1985).

Separate flow meters were used for each treatment. Water to furrows was applied using gated pipes.

Tomato

The tomato study was conducted in two plastic greenhouses, constructed in a north–south direction and of

15� 24m size. The plastic cover was 150mmUVþ IRþ antifog added polyethylene. The soils of the greenhouses

were the same as the cotton field soils.

Following a deep ploughing, the greenhouse soil was solarised in August. Seedlings of fresh market tomato

(Lycopersicum esculentum L., cv. F1 Fantastic, Israeli origin) were transplanted on 4 October 2001 and

immediately irrigated with 3 l of initial establishment water per plant. Three irrigation treatments, arranged in a

randomised complete block experiment design with four replicates, were tested: (1) FULL, control treatment where

the full amount of irrigation water, based on Class-A pan evaporation data, was applied to both halves of the plant

root zone; (2) 1PRD, 50% deficit irrigation with PRD in which wetted and dry sides of the root zone were

interchanged every irrigation; (3) DI, 50% deficit irrigation, applied to both halves of the plant root zone, with no

PRD effect (Table I). Each of the two greenhouses allocated for this study had two replicates. Replicated sub-plots

of each irrigation treatment were 10.5� 2.4m (25.2m2) in size and had 3 rows of 21 plants, with 0.8m row spacing.

The plant spacing in rows was 0.5m. Fertilisers of N, P and K at concentrations of 100, 30 and 150mg l�1,

respectively, were continuously fed with irrigation water, applied to the FULL treatment. The concentrations were

adjusted for the other treatments, DI and 1PRD, in proportion to the deficit level of irrigation water, to ensure that all

the treatments received the same amount of fertiliser. Concentration of K was increased by 50% on two occasions at

123 and 143 days after transplanting (DAT) to prevent bottom rot disorder (spotted maturating) of the tomato fruits.

EC of irrigation water with fertiliser added was around 0.85 dSm�1. The irrigation interval was kept at once a

week until the fruit-setting stage, and it was increased to twice weekly from thereon until harvest. In so doing,

Table I. Description of treatments

Treatment Description Plants (year of experiment)

FULL FULL irrigation with all roots wetted Cotton (2000) and tomato (2001)DI All roots wetted but received 50% less water,

compared to FULL irrigationTomato (2001)

1PRD Compared to FULL irrigation 50% less water was applied;irrigated sides of the root zone were alternated every irrigation

Cotton (2000) and tomato (2001)

2PRD Compared to FULL irrigation 50% less waterwas applied; irrigated sides of the root zone werealternated every other irrigation

Cotton (2000)

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536 H. KAMAN ET AL.

maximum water application was maintained at 6 l or less per plant as suggested by Kirda et al. (2004) to prevent

deep percolation, which was controlled with the combined use of the neutron gauge and tensiometers. A class-A

evaporation pan located in the centre of one of the greenhouses was used to estimate irrigation water requirement

(I, mm) for the FULL treatment using the equation

I ¼ K � Ep

where K is the coefficient comprising plant coverage, wetted area and pan coefficient; Ep is cumulative evaporation

(mm), measured in a class-A pan during the allowed irrigation interval. As recommended earlier by Cevik et al.

(1996), the coefficient K was allowed to change from 0.30 to 1.25 as the season progressed.

Irrigation water use efficiency (IWUE) for tomato and cotton crops used to evaluate the comparative benefits of

the irrigation treatments was calculated using the following equation (Kirda et al., 2004):

IWUE ¼ Y

I

where Y is yield (kg ha�1) and I is seasonal irrigation water (mm) applied in different irrigation treatments.

Soil sampling for the salinity assessment

Two sets of soil samples were collected for both the cotton and tomato studies, essentially following a similar

sampling scheme, viz. at the start and end of the season.

Initial sampling. Immediately following the sowing of cotton, composite soil samples from 5, 15, 25, 45, 75 and

105 cm soil depths with three replicates were collected to assess initial soil salinity status before the start of the

irrigation season. Similarly, the samples for the tomato study were collected from 5, 20, 40 and 60 cm soil depths at

the transplanting stage.

End of season sampling. To determine salinity profiles in the root zone for each treatment, triplicate soil samples

from the same depths of initial sampling were collected, right after the harvest of cotton and at the end of the

greenhouse season. Additionally, a total of 30 and 20 soil samples were collected from the root zones of cotton and

tomato, respectively, using a grid sampling scheme. The samples were analysed for ECe, and the data were used to

construct plant root zone salinity maps.

The soil samples were analysed for ECe (dSm�1) measurements of soil saturation extracts, following the

procedure described by Richards (1954). The salinity maps were constructed using the inverse-distance-weighing

(IDW) algorithm described in Isaaks and Srivastava (1989) and utilising the same parameters used earlier by Cetin

and Diker (2003). The maps facilitated assessment of comparative differences of end-of-season salt accumulation

under different irrigation treatments.

RESULTS AND DISCUSSION

Cotton

During irrigation, soil water content in plant root zone was brought up to field capacity (100% of PAWC), under

FULL irrigation; however, it could only reach 65–75% of PAWC under 1PRD and 2PRD, where the wet and

partially dry halves of the root zone were alternated every and every other irrigation, respectively. The root zone

capillary pressure was highest under FULL irrigation, following the same trend demonstrated with soil water status

(Figure 1). There was no difference between the 1PRD and 2PRD treatments as regards both capillary pressure and

water content, and they were both proportionally drier compared to FULL irrigation throughout the season. The

root zone soil water status and capillary pressure graphs clearly showed that half of the plant root zone under the

PRD practice was drier throughout the irrigation season (Figure 1), in comparison with the other half of the root

zone. In spite of 50% reduced irrigation water application in the 1PRD and 2PRD treatments, the cotton seed yields

were only marginally decreased, 3.0–6.4%, compared to the FULL treatment (Figure 2). However, irrigation water

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IRRIGATION AND SALT ACCUMULATION WITH PARTIAL ROOT-DRYING TECHNIQUE 537

use efficiency (IWUE) and cotton seed yield for unit irrigation water application (kg ha�1mm�1), increased nearly

twofold (88–95%) when deficit irrigation was applied with the PRD effect. Similar results were reported for many

other crops (e.g. Zegbe-Dominguez et al., 2003; Kirda et al., 2004, 2005).

Soil salinity profiles indicated that salt accumulation under FULL irrigation treatment was proportionally lower

in surface soil layers within 30 cm depth, compared to the PRD treatments (Figure 3). However, there was

essentially no difference among treatments in soil layers below 30 cm depth, and the salinity increased by only

0.2 dSm�1, compared to the initial salinity level.

The salinity maps of the cotton root zone also confirmed that differences in salt accumulation were limited to

30 cm soil depth (Figure 4). Soil salinity increased toward the ridges of plant rows, with proportionally the lowest

salinity recorded under FULL irrigation (Figure 4). Soil ECe showed high spatial variability within the 30 cm soil

layer under PRD treatments. The salinity level encountered was far below the salt tolerance threshold of cotton,

0

15

30

45

60

75

1501251007550

DAYS AFTER SOWING

CA

PIL

LA

RY

PR

ES

SU

RE

(-k

Pa

)

FULL 1PRD-WET 1PRD-DRY

FC

200

300

400

500

600

mc021m

m(E

GA

RO

TS

RE

TA

WLI

OS

1-)

PWP

FC

Figure 1. Changes in soil water storage and capillary pressure, shown separately for wet and partially dry halves of the cotton root zone

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538 H. KAMAN ET AL.

which is among the most salt tolerant field crops (Ayers and Westcot, 1985). Cotton growth and yield are not

influenced at soil salinities as high as 7.7 dSm�1. In another study by Vulkan-Levy et al. (1998), it was shown

that irrigation water with EC of 4–5 dSm�1 had no effect on cotton yield. Soil salinity accumulating at the end

of the irrigation season was about double initial soil salinity; however, no significant difference existed among the

Figure 2. Cotton seed yield and IWUE. The vertical line bars show means (n¼ 3)�SE. Bars with different letters show significantly differentdata, based on Tukey’s mean range test at a¼ 0.01 rejection level. NS and figures in parentheses stand for no significance and seasonal irrigation

water applied, respectively

0

15

30

45

60

75

90

105

0.0 0.4 0.8 1.2 1.6

ECe (dS m-1)

mc(H

TP

ED

)

INITIAL FULL 2PRD 1PRD

Figure 3. Salt accumulation in the root zone of furrow-irrigated cotton at the initial stage and at harvest. Data points show means (n¼ 3).Tukey’s critical values for comparison at a¼ 0.01 rejection level are shown by line bars

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IRRIGATION AND SALT ACCUMULATION WITH PARTIAL ROOT-DRYING TECHNIQUE 539

irrigation treatments except within the surface layer of 20 cm depth (Figures 3 and 4). Therefore, the PRD practice

introduced no additional salinity risk if used in soils with no salinity problem and with good quality water available.

Future studies should consider testing PRD practice using inferior quality water, which should be used cautiously

for their probable salt accumulation risks.

Figure 4. Salinity map in the root zone of furrow-irrigated cotton at harvest

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540 H. KAMAN ET AL.

Tomato

Data on comparative fruit yield response of tomato to FULL and deficit irrigation treatments, which were either

imposed through conventional deficit irrigation (DI) or with the PRD effect (1PRD), have been published elsewhere

(Kirda et al., 2004). Furthermore, IWUE results for tomato crop grown under FULL and deficit irrigation

treatments were discussed in detail by Kirda et al. (2004). Therefore, discussions will be limited here to soil

salinisation. Root zone soil water content, not shown here, was 20–25% lower under deficit irrigation treatments

(DI and 1PRD) throughout the growing season, compared to FULL irrigation.

Similar to the findings of the cotton study, the highest salt accumulation occurred within 20 cm depth of the

surface layer, and the lowest accumulation occurred under FULL irrigation (Figure 5). Subsoil salt accumulation

under FULL and 1PRD treatments was almost alike, whereas it was higher under DI compared to other treatments.

Although the 1PRD treatment received 50% reduced irrigation, leaching in one half of the root zone, which was

alternately changed, was as effective as under FULL irrigation. The leaching under the 1PRD treatment took place

at comparatively lower water content and pore-water velocity, which increased the effectiveness of leaching (Kirda

et al., 1974).

The salinity maps showed that the highest salt accumulation occurred near the drippers and the plant roots were

relatively free of salts under FULL irrigation (Figure 6). The salts under DI were concentrated near to plant roots,

with the highest accumulation observed within 5–10 cm depth. The salt distribution under 1PRD exhibited no

symmetry, which might have been caused by alternating wetting and drying processes, and thus the salt

accumulation zone was shifted toward one of the drippers, essentially leaving the plant root zone free of salts,

similar to FULL irrigation (Figure 6). Although a yield reduction of 17.3%, observed under the 1PRD treatment,

which may be of high economic value compared to FULL irrigation, was not found to be statistically significant

(Kirda et al., 2004), it should not be attributed to salt accumulation, which never reached tomato salt tolerance

threshold levels (Figures 5 and 6). It is more likely that the imposed irrigation deficit of the order of 50% was too

high for tomato.

It is well documented that salinity hinders plant development and reduces crop yields (Romero-Aranda et al.,

2001), although the salinity effect depends on plant species. Small increases in salt accumulation under the deficit

irrigation treatments (DI and 1PRD), compared to FULL irrigation, had no significant effect on tomato yield. High

0

20

40

60

0 2 4 6 8 10

ECe (dS m-1)

)mc(

HT

PE

D

INITIAL FULL DI 1PRD

Figure 5. Salt accumulation in the root zone of drip-irrigated tomato at the initial stage and the end of the irrigation season. Data points showmeans (n¼ 3). Tukey’s critical values for comparison at a¼ 0.01 rejection level are shown by line bars

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IRRIGATION AND SALT ACCUMULATION WITH PARTIAL ROOT-DRYING TECHNIQUE 541

salt tolerance of tomato must also have contributed to the observed behaviour. The maximum salinity (ECe)

encountered throughout the season in the root zone was about 7.5 dSm�1 (Figure 5), which was equivalent to soil

water ECe of approximately 3.0 dSm�1. However, the differences of average soil salinity under the DI and 1PRD

treatments were not statistically significant (Figure 5). No adverse effect on tomato yield was reported at irrigation

water EC as high as 3–4 dSm�1 (Cuartero and Fernandez-Munoz, 1999). Therefore, salt accumulation is not

expected to be a constraint limiting tomato fruit yield if PRD practice is adapted for saving water. It should also be

recognised that deficit irrigation imposed through the PRD effect enhances fruit quality (Chaffey, 2001) and that

maximum salt accumulation under PRD practice occurs somewhat far from plant stems.

Figure 6. End of season salinity map in the root zone of drip-irrigated tomato

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542 H. KAMAN ET AL.

CONCLUSIONS

There was no measurable difference encountered in salt accumulation under PRD irrigation, compared to FULL

treatment, tested for cotton. The maximum salt accumulation, which largely depends on initial soil salinity and

irrigation water quality, was 1.3 dSm�1, a value well below the salt tolerance threshold level (7.7 dSm�1) of cotton.

If one adopts deficit irrigation through the PRD effect under scenarios of recurrent drought and shortage of

irrigation water supplies, there will be no risk of salt accumulation if soils initially have no salinity problem and

available irrigation water is of good quality.

There was about 65% increase of ECe in tomato-grown greenhouse soils with initial soil ECe of 2.0 dSm�1,

when irrigated with the PRDmethod, compared to FULL irrigation. However, the measured increase in soil salinity

was limited to only surface soil layers of 5 cm depth. The levels of soil salinity measured within tomato root

zone was not at the extent of adversely influencing fruit yield and therefore one can safely adapt the PRD practice if

there is shortage of irrigation water supplies. However, greenhouse soils should be leached, as is usually practised,

of excess salts before the start of the new cropping season.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge that this work was financially supported by the European Union through

INCO-MED IRRISPLIT RTD project of contract ICA3-CT-1999-00008. We wish to thank Cukurova University

Scientific Research Projects Unit for the partial financial support of this work. Our special thanks are due to Helene

Bayard Can, lecturer at the Department of Foreign Language Teaching, Faculty of Education, University of

Cukurova, Adana, Turkey, for a French translation of the title, abstract and key words of the paper. The comments

of three anonymous reviewers substantially improved the paper.

REFERENCES

Ayers RS, Westcot DW. 1985. Water quality for agriculture. FAO Irrigation and Drainage Paper 29, Rev. 1, Rome, Italy.

Cetin M, Diker K. 2003. Assessing drainage problem areas by GIS: a case study in the eastern Mediterranean region of Turkey. Irrigation and

Drainage 52: 343–353.

Cevik B, Baytorun N, Tanriverdi C, Abak K, Sari N. 1996. Effect of different irrigation water applications yield and quality of eggplant grown in

glasshouse (in Turkish with English abstract). Turkish Journal of Agriculture and Forestry 20: 175–181.

Chaffey N. 2001. Restricting water supply enhances crop growth. Trends in Plant Science 6: 346 pp.

Cuartero J, Fernandez-Munoz R. 1999. Tomato and salinity. Scientia Horticulturae 78: 83–125.

Davies WJ, Zhang J. 1991. Root signals and the regulation of growth and development of plants in drying soil. Annual Review of Plant

Physiology and Plant Molecular Biology 42: 55–76.

Dinc U, Sari M, Senol S, Kapur S, Sayin M, Derici MR, Cavusgil V, GokM, Aydin M, Ekinci H, Agca N, Schlichting E. 1995. Soils of Cukurova

Region (in Turkish with extended English abstract), 2nd edn. Publication of Agricultural Faculty, Univ. of Cukurova, no 26: Adana, Turkey.

IAEA (International Atomic Energy Agency). 1995.Management strategies to utilize salt affected soils. IAEA-TECDOC-814, ISSN 1011-4289,

Vienna, Austria, p. 64.

Isaaks EH, Srivastava RM. 1989. An Introduction to Applied Geostatistics. Oxford University Press, Inc.: New York; 561 pp.

Jones HG. 1992. Plants and Microclimate: a Quantitative Approach to Environmental Plant Physiology, 2nd edn. Cambridge University Press:

Cambridge.

Kang S, Lıang Z, Hu W, Zhang J. 1998. Water use efficiency of controlled alternate irrigation on root-divided maize plants. Agricultural Water

Management 38: 69–76.

Karaata H. 1985. Harran ovasinda pamuk su tuketimi arastirmasi (in Turkish). K.H.G. Mud. Sanliurfa Arst. Enst. Yay., Sanliurfa, Turkey, no 24:

15–36.

Kirda C, Nielsen DR, Biggar JW. 1974. The combined effects of infiltration and redistribution on leaching. Soil Science 117: 323–330.

Kirda C, Moutonnet P, Hera C, Nielsen DR (eds). 1999. Crop Yield Response to Deficit Irrigation. Kluwer Academic Publishers: Dordrecht, The

Netherlands.

Kirda C, Cetin M, Dasgan Y, Topcu S, Kaman H, Ekici B, Derici MR, Ozguven AI. 2004. Yield response of greenhouse grown tomato to partial

root drying and conventional deficit irrigation. Agricultural Water Management 69: 191–201.

Kirda C, Topcu S, Kaman H, Ulger AC, Yazici A, Cetin M, Derici MR. 2005. Grain yield response and N-fertiliser recovery of maize under

deficit irrigation. Field Crops Research 93: 132–141.

Copyright # 2006 John Wiley & Sons, Ltd. Irrig. and Drain. 55: 533–544 (2006)

DOI: 10.1002/ird

IRRIGATION AND SALT ACCUMULATION WITH PARTIAL ROOT-DRYING TECHNIQUE 543

Masoud FI. 1981. Salt affected soils at a global scale and concepts for control. FAO Land and Water Development Division, Technical Paper,

Rome, Italy, 21 pp.

Ozbek H, Dinc U, Kapur S. 1974. Cukurova universitesi yerlesim sahası topraklarinin detaylı etut ve haritası (in Turkish). C. U. Zir. Fak. Yay.,

Adana, Turkey, no 23, 149 pp.

Richards LA (ed.). 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Agric. Handbook 60: Washington; 160 pp.

Romero-Aranda R, Soria T, Curtero J. 2001. Tomato plant-water uptake and plant-water relationship under saline growth conditions. Plant

Science 160: 265–272.

Stoll M, Loveys B, Dry P. 2000. Hormonal changes induced by partial rootzone drying of irrigated grapevine. Journal of Experimental Botany

51: 1627–1634.

Szabolcs I. 1989. Salt-affected Soils. CRC Press, Inc.: Boca Raton, Fla.; 274 pp.

Vulkan-Levy R, Ravina I, Mantell A, Frenkel H. 1998. Effect of water supply and salinity on pima cotton. Agricultural Water Management 37:

121–132.

Zegbe-Dominguez JA, Behboudian MH, Lang A, Clothier BE. 2003. Deficit irrigation and partial root zone drying maintain fruit dry mass and

enhance fruit quality in ‘Petopride’ processing tomato (Lycopersicon esculentum, Mill.). Scientia Horticulturae 98: 505–510.

Copyright # 2006 John Wiley & Sons, Ltd. Irrig. and Drain. 55: 533–544 (2006)

DOI: 10.1002/ird

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