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Scientia Horticulturae 162 (2013) 31–38

Contents lists available at ScienceDirect

Scientia Horticulturae

journa l h om epage: www.elsev ier .com/ locate /sc ihor t i

he combined effects of phosphorus and zinc on evapotranspiration,eaf water potential, water use efficiency and tuber attributes ofotato under water deficit conditions

. Motalebifarda,∗, N. Najafia, S. Oustana, M.R. Nyshabouria, M. Valizadehb

Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, IranDepartment of Plant Breeding and Biotechnology, Faculty of Agriculture, University of Tabriz, Tabriz, Iran

r t i c l e i n f o

rticle history:eceived 8 February 2013eceived in revised form 30 June 2013ccepted 30 July 2013

eywords:hosphorusotatooil moistureuber attributesinc

a b s t r a c t

This study was conducted for evaluating the combined effect of soil moisture, phosphorus (P) and zinc(Zn) levels on crop evapotranspiration (ET), leaf water potential (LWP), water use efficiency (WUE) andvarious tuber attributes of potato (Solanum tuberosum L. cv. Agria) under greenhouse conditions. Thisinvestigation was conducted as a factorial experiment based on randomized complete blocks designwith Zn at three levels (0, 10 and 20 mg Zn per kg dry soil as ZnSO4·7H2O), P at three levels (0, 30 and60 mg P per kg dry soil as Ca(H2PO4)2·H2O) and soil moisture at three levels (0.5 FC–0.6 FC, 0.7 FC–0.8 FCand 0.9 FC–FC) using three replications. The various attributes of potato tubers including tuber numbers,dry matter content (DM), yield, WUE and indicators of water deficit stress intensity (ET and LWP) weremeasured routinely during the crop growth period. The results showed that the water deficit stressresulted in a significant decrease in ET, tuber numbers, yield and WUE. Application of P significantlyincreased the ET, tuber numbers and yield and Zn application significantly affected the tuber numbers.

The P × soil moisture interaction effect was significant for ET, LWP, tuber numbers and yield. Whilethe Zn × soil moisture interaction was significant only for yield. The results showed that the two wayinteractions of Zn, P and soil moisture were mainly synergistic on the most of above mentioned attributes.In general, to achieve the optimum yield of potato tubers in similar soils, application of 10 mg Zn and30 mg P per kg of dry soil could be recommended under full-irrigated conditions. The regression analysisshowed that the yield of potato was increased by application of P under water deficit conditions.

. Introduction

In natural environments, plants are subjected to many stresseshat can have negative effect on growth, metabolism, and yield.iotic (insects, bacteria, fungi, and viruses) and abiotic (light, tem-erature, water availability, nutrients, and soil structure) factorsffect the growth of higher plants. Among these, water deficit is aajor abiotic factor that limits crop production (Reddy et al., 2004).

otato production is ranked fourth (based on production) in theorld after rice, wheat, and maize with the production of 321 mil-

ion tons from 19.6 million hectares (FAOSTAT, 2007). In Iran this

Abbreviations: ABA, abscisic acid; ANOVA, analysis of variance; CCE, calciumarbonate equivalent; DM, dry matter content; ET, crop evapotranspiration; FC, fieldapacity; IAA, indoleacetic acid; LWP, leaf water potential; P, phosphorous; ROS,eactive oxygen species; SOD, superoxide dismutase; WUE, water use efficiency;n, zinc.∗ Corresponding author. Tel.: +98 4116678173; fax: +98 4113356006.

E-mail addresses: r.motalebifard@tabrizu.ac.ir,otalebifard@gmail.com (R. Motalebifard).

304-4238/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.scienta.2013.07.043

© 2013 Elsevier B.V. All rights reserved.

important crop is ranked third after wheat and tomatoes with theproduction of 4.05 million tons (FAOSTAT, 2010). Potato is a tem-perate crop, growing and yielding well in cool and humid climatesor seasons, but it is also cultivated in tropical to sub-polar cli-matic regions, and represents a major food crop in many countries(Shalhevet et al., 1983; Ierna and Mauromicale, 2012). Water supplyis a major limiting factor in the production and quality of potato.It is known to be sensitive to water deficit (Fabeiro et al., 2001;Ierna and Mauromicale, 2012) due to its sparse and shallow rootsystem, and tuber yield might be reduced considerably in responseto soil moisture deficit (Deblonde and Ledent, 2001; Ahmadi et al.,2010). Water deficit stress influences the development and growthof potato shoot, root and tubers. For example, leaf area index, stemheight and ground coverage of potato are reduced under waterdeficit stress conditions (Deblonde and Ledent, 2001; Yuan et al.,2003; Fleisher et al., 2008). The impact of water deficit on plants

depends on time (Fleisher et al., 2012b), duration and severity ofstress (Jefferies, 1995). At all growth stages, water deficit stressreduces photosynthetic efficiency, but water deficit stress has themost drastic effect on the tuber yield during the tuber initiation and

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ulking stages (Önder et al., 2005). Fleisher et al. (2012a) showedhat potato dry matter reduced proportionately by drought cyclest both vegetative and post tuber initiation periods comparing withontrol.

The nutrients such as K, Zn and P perform important role in pro-ecting plant from water deficit stress damage. Zn has been foundo be a vitally important micronutrient in crop production and itseficiency has been shown to be more widespread throughout theorld than those of any other micronutrient (Alloway, 2008). Zn has

n important role in improvement of water deficit stress effects inlants. Zn has functional role in maintaining the structural integritynd controlling permeability of biomembranes (Cakmak, 2000). Inn deficiency conditions, plant cells loss their membrane integrityhat results in higher membrane permeability to inorganic ionsWelch et al., 1982). Apart from its role as a structural component in

embranes, Zn also plays a key role in controlling the generationnd detoxicification of reactive oxygen species (ROS), which canamage membrane lipids and sulphydryl groups (Alloway, 2008).n exerts an inhibitory action on membrane damage catalyzed byOS (Cakmak, 2000). In general, it would appear that the major rolef Zn in membranes is to protect membrane lipids and proteinsrom peroxidation caused by the ROS (Alloway, 2008). The level ofn nutrition may also affect plant water relations and alter stomatalonductance (SC). Sharma et al. (1984) reported that Zn deficiencyn cabbage decreased osmotic potential and relative water con-ent compared to plants grown with an adequate supply of Zn.ranspiration rate, SC, and WUE also declined under Zn deficiencyonditions (Khan et al., 2004). Although, Zn is required directly foruperoxide dismutase (SOD) enzyme activity and indirectly for highctivity of the enzymes involved in H2O2 detoxification such asatalase, ascorbate peroxidase and glutathione reductase (Cakmak,000).

P deficiency in plants is the second most yield limiting nutrientfter nitrogen. Its fertilization helps plants overcome or decreaseater deficit stress damages. Water deficit and P deficiency stressesay be related because water deficit stress can reduce P concen-

ration in stand biomass by reducing soil organic P mineralizationates (Sardans and Penuelas, 2005) and transforming of P to non-vailable forms (Sardans et al., 2006; Sardans and Penuelas, 2007).he low availability of P in soil often restricts root growth andeduces access to subsoil moisture (Pathuluri et al., 1986). P defi-iency affects the response of a plant to water deficit stress dueo effect on stomata behavior and on the resistance to water flowithin the plant. P-deficient plants close their stomata at higher

WP (less negative) than those receiving an adequate P supplyGarg et al., 2004).

Limited studies have been conducted on the combined effectsf Zn and P on potato production (Soltanpour, 1969; Chaverri andornemisza, 1977; Trehan and Grewal, 1983; Sohota, 1985; Trehannd Sharma, 2000; Barben et al., 2010a; Barben et al., 2010b; Orojind Golchin, 2012), but none of them have been carried out underater deficit conditions. Therefore, the aims of this study were to

valuate (a) effect of soil moisture on tuber yield, yield components,nd other measured parameters, (b) combined effect of Zn and Pn potato tuber attributes under water deficit conditions, (c) Znnd P fertilizer requirement of potato under different soil wateronditions, (d) ability of Zn and P to alleviate water deficit effectsn potato tuber yield.

. Materials and methods

.1. Greenhouse and soil description

A pot experiment was conducted in a naturally lighted green-ouse at Agricultural Research Station of Tabriz University, Iran

ticulturae 162 (2013) 31–38

during 2012. The maximum and minimum temperature of green-house was measured daily and a big hydroelectric cooler was usedfor controlling greenhouse temperature. The average maximumand minimum of temperature was 32.5 and 11.5 ◦C during plantingperiod, respectively. Relative humidity of greenhouse was main-tained about 65% by periodic moisturizing of the greenhouse floor.At first, a calcareous non-saline soil (EC = 0.47 dS m−1) low in avail-able P and Zn (Olsen-P = 8.7 and DTPA-Zn = 0.5 mg kg−1 that werelower than the critical levels) was selected (Alloway, 2008). Thesoil was taken from Espiran village in northwest of Tabriz (Iran)with the latitude of 38◦15′57′′ N and longitude of 46◦19′53′′ E fromdepth of 0–25 cm. After air drying and sieving (2 mm in diameter),soil properties such as available-P by Olsen method, available-Zn,Mn, Fe and Cu by DTPA-TEA, available-K by 1 N acetate ammo-nium extraction, pH in a 1:1 soil/water ratio suspension, EC in a 1:1soil/water solution and soil texture by hydrometric method weremeasured (Gee and Bauder, 1986; Sparks et al., 1996) and presentedin Table 1.

2.2. Treatments and planting description

The experiment was arranged as factorial 3 × 3 × 3 with n = 3based on randomized complete blocks design with three factorsincluding Zn at three levels of 0, 10 and 20 mg Zn per kg of soilas ZnSO4·7H2O, P at three levels of 0, 30 and 60 mg P per kg of soilas Ca(H2PO4)2·H2O (monocalcium phosphate), and soil moisture atthree levels of 0.5 FC–0.6 FC, 0.7 FC–0.8 FC and 0.9 FC–FC in threereplications that all of them planted at same time (04/26/2012)with total 81 pots.

Based on soil testing, 5 mg Fe as Sequestrine-138 (EDDHA-FeNa),5 mg Mn as MnSO4·H2O and 200 mg of N (one-third at planting andthe rest in two split until soil moisture treatments imposing) asurea ((NH2)2CO) were applied per kg of soil. Then, 10 kg of abovementioned soil by bulk density of 1.1 g per cm3 of soil was pouredinto each pot (30 cm diameter and 26 cm height) and two potatotubers (Solanum tuberosum L.) cv. Agria with certified seeds anduniform sizes (45–55 mm) were planted in 10 cm depth of pots soil.Two tubers were planted to avoid elimination possibility of a potbecause of plant death and need to a large number of leaves formeasuring many parameters such as LWP, RWC, enzymes activ-ity and nutrients concentrations that were not presented in thismanuscript. The position of the pots within each block was changedonce to twice per week to minimize the effects of light and tem-perature gradients within the greenhouse as well as border effects.

Pots were irrigated equally and uniformly at 0.94 ± 0.05 FC fromsowing until flowering (64 days) and then soil moisture levels wereimposed three weeks from the flowering (64th day) until harvest(85th day after planting). Throughout the experiment, soil moisturewas controlled by pots weighting and watering two times per day.Deionezed water was added by graduated cylinder according topots weight reduction from the intended soil moisture levels (upto 0.95 FC until flowering and up to 0.6 FC, 0.8 FC and FC duringsoil moisture imposing period). To compensation of plant weightincreasing effect, additional pots were used for each of soil moisturelevels. The whole plant fresh weight was determined every twoweeks, and the weight correction was done.

2.3. Parameters measurements

Moisture of field capacity (FC) was determined by the pressureplate method at pressure of 300 kPa (Kirkham, 2004) and was 18.5%.

For evaluating the stress intensity, LWP (as a direct indicator

of soil water status (Zhu et al., 2004)) and SC were measured onthree leaves from each pot by pressure chamber (Model OSK2710,OGAWA Seiki Japan) and leaf porometer AP4 (Delta-T Devices-UK) around midday during the period that water deficit stress was

R. Motalebifard et al. / Scientia Horticulturae 162 (2013) 31–38 33

Table 1Some physical and chemical properties of soil.

Texture CCE (%) SP (%) FC (%) OC (%) pH (1:1) EC (1:1) (dS m-1) P (mg kg−1) K (mg kg−1) Fe (mg kg−1) Zn (mg kg−1) Mn (mg kg−1) Cu (mg kg−1)

Clay loam 15.25 44.4 18.5 0.5 7 0.47 8.7 556 3.98 0.52 7.01 2.2

CCE, calcium carbonate equivalent; SP, saturation percentage; FC, field capacity; EC, electrical conductivity; OC, organic carbon.

Table 2Summary of variance analysis (mean squares) for the measured attributes of potato.

Source of variation df ET LWP Tuber numbers SC Tuber yield Stem height DM WUE

Replication 2 47.4ns 8032ns 2.93* 0.002ns 4122ns 15.85ns 0.05ns 13.0ns

Moisture 2 46288.0*** 1510873*** 4.78** 1.86*** 340617*** 340.43*** 25.61*** 208.0***

Zn 2 51.2ns 9054ns 8.48*** 0.049ns 5370ns 76.91** 2.33ns 15.3ns

Zn × moisture 4 170.0ns 14233ns 1.93ns 0.073** 8049* 20.04ns 1.45ns 29.7ns

P 2 3484.0*** 69635** 10.48*** 0.157*** 56364*** 563.92*** 0.72ns 15.7ns

P × moisture 4 475.0** 76604*** 2.37* 0.122*** 8472* 22.84ns 0.51ns 10.0ns

Zn × P 4 68.2ns 79935*** 2.91* 0.088** 655ns 6.07ns 0.72ns 2.6ns

Zn × P × moisture 8 243.0* 40413** 5.57** 0.041* 5449ns 15.99ns 1.22ns 13.6ns

Error 52 102.0 10373 0.84 0.019 3298 13.83ns 1.32 12.9ns

ET: crop evapotranspiration; LWP: leaf water potential; SC: stomatal conductance; DM: dry matter; WUE: water use efficiency.ns, non-significant

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were significant for evapotranspiration (ET) (Table 2).Fig. 2 shows ET for different soil moisture and P combined

treatments. The maximum (128.0 mm) and minimum (23.5 mm)of ET was obtained by application of 60 mg P per kg of soil under

* Significant at p ≤ 0.05.** Significant at p ≤ 0.01.

*** Significant at p ≤ 0.001.

mposed. ET was calculated for the test period (flowering until har-est) from the soil water balance (Eq. (1)) according to Howell et al.1995):

T = I + P − D ± �S (1)

here, ET is the crop evapotranspiration (mm), I is the depth ofpplied irrigation water (mm), P is the precipitation (mm), D is therainage water below the root zone (mm), and �S is the soil waterepletion at harvest (mm). Because of greenhouse conditions and

ack of drain hole in the bottom of the pots, the precipitation andrainage water were considered to be zero.

Tubers were harvested at the end of soil moisture levels impos-ng period (after three weeks and with total growth period of 85ays). At harvest time, tuber numbers (>10 mm), and total fresheight of tubers (>10 mm) were determined. WUE was calculated

y dividing total tuber fresh weight (g pot−1) by total water con-umption (L pot−1) (Ierna et al., 2011). DM was determined byrying of sliced tubers at 75 ◦C for 48 h and from the Eq. (2) accord-

ng to Tekalign and Hammes (2005):

M(%) = weight of dried tuber sliceweight of fresh tuber slice

× 100 (2)

.4. Statistical analysis of data

Data were subjected to analysis of variance as factorial 3 × 3 × 3ith n = 3 based on randomized complete blocks design by usingSTATC software. Tukey’s test at p ≤ 0.05 probability level was

pplied to compare the mean values of measured attributes. Thexcel software (Excel software 2007, Microsoft Inc., WA, USA) wassed to draw figures.

. Results

.1. Leaf water potential

The analysis of variance (ANOVA) showed that the main effectsf soil moisture and P, two way interactions of P × soil moisture

nd Zn × P and three way interaction of soil moisture × Zn × P wereignificant for leaf water potential (LWP) (Table 2).

The effect of soil moisture × P interaction on LWP is shown inig. 1. The lowest amount of LWP (−1043 kPa) was observed in the

without P under severe water deficit stress conditions (0.5 FC–0.6FC) which increased 2.35 times in the 30 mg P per kg of soil underfull-irrigated conditions (0.9 FC–FC). P had no effect on LWP insevere water deficit conditions but LWP was decreased in moderatewater deficit conditions (0.7 FC–0.8 FC) by P application.

The three way interaction of soil moisture × Zn × P (Table 4)showed that the lowest amount of LWP was observed under full-irrigated conditions and was decreased by water deficit stress.According to Table 4 and under full irrigated conditions, applica-tion of 30 mg P per kg of soil mainly increased LWP comparing withwithout P application. It was while that application of 60 mg P perkg of soil decreased LWP at 0.7 FC–0.8 FC soil moisture level. Undersevere water deficit conditions, application of 30 mg P and 10 mg Znper kg of soil decreased LWP significantly comparing with withoutP and 20 mg Zn per kg of soil.

3.2. Crop evapotranspiration

The main effects of soil moisture and P, two way interaction ofsoil moisture × P and three way interaction of soil moisture × Zn × P

Fig. 1. Leaf water potential (LWP) in response to P and soil moisture interaction(n = 9).

34 R. Motalebifard et al. / Scientia Horticulturae 162 (2013) 31–38

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Water use efficiency (WUE) for potato in this study was signifi-cantly affected by soil moisture levels but the main and combinedeffects of other factors were not significant on this (Table 2). Waterdeficit significantly decreased WUE and the lowest value of this

Fig. 2. Crop evapotranspiration (ET) a

ull-irrigated condition and without P under severe water deficitondition, respectively. The three way interaction of soil mois-ure × Zn × P (Table 4) showed that water deficit stress decreasedT significantly and higher amount of ET was obtained in full-rrigated conditions, so that ET was decreased 5.9 times in withoutn and P application under severe water deficit condition relative to0 mg Zn and 60 mg P per kg of soil under full-irrigated condition.he differences of P fertilizer levels were significant only in full-rrigated conditions and application of P increased ET especially

ith application of 10 mg Zn per kg of soil. While in severe watereficit conditions, ET had no significant differences between P lev-ls (Table 4). Table 4 also showed that application of Zn increasedT under full-irrigated conditions slightly but under severe watereficit conditions Zn application had not significant effect on ET.

.3. Tuber numbers

The ANOVA showed that the main effects of soil moisture, P andn and P × soil moisture, Zn × soil moisture, Zn × P and Zn × P × soiloisture interactions were significant for tuber numbers (Table 2).The three way interaction of Zn × P × soil moisture (Table 4)

howed that tuber numbers were lower under severe water deficitonditions comparing with other soil moisture levels. Applicationf 10 mg Zn per kg of soil under full-irrigated and moderate watereficit conditions was the best level and the tuber numbers wereignificantly decreased (2.3 times) in without P and Zn applicationnder 0.5 FC–0.6 FC condition. Application of Zn increased tuberumbers especially in without P under all of soil moisture condi-ions and the kind of P × Zn interaction on the tuber numbers wasepended on the level of P and Zn application. Under full irrigatedonditions, P application affected the tuber numbers and 60 mg Per kg of soil increased the tuber numbers compared with otheroil moisture levels. It was while that at moderate water deficitonditions, the effect of P application on the tuber numbers wasignificant under 10 or 20 mg Zn per kg of soil levels. It could beentioned that under severe water deficit conditions, the highest

uber numbers was observed in level of 30 mg P per kg of soil.

.4. Tuber yield

The main effects of soil moisture and P and two way interac-ions of Zn × soil moisture and P × soil moisture were significantor potato tuber yield (Table 2). The calculated tuber yield for Znnd soil moisture combined treatments are shown in Fig. 3. The

rent soil moisture and P levels (n = 9).

highest tuber yield (494.3 g pot−1) was observed in application of20 mg Zn per kg of soil under full-irrigated conditions which wasdecreased approximately 2 times at severe water deficit conditions.Means comparison showed that Zn application had not significanteffect on tuber yield under sever water deficit conditions, whereas,at higher levels of soil moisture, tuber yield increased with increas-ing Zn rates. Tuber yield increased by water supply especially inapplication of 20 mg Zn per kg of soil conditions and interaction ofsoil moisture × Zn was synergistic on tuber yield (Fig. 3). The resultsshowed that the interaction of soil moisture × P on tuber yield wasmostly similar to the combined effects of soil moisture and Zn onyield (Fig. 4).

3.5. Dry matter percentage and water use efficiency

Table 2 shows that the main effect of soil moisture was sig-nificant on DM percentage but other main and interactions werenot significant. Water limitation resulted in higher DM percent-age compared with well watering. The DM percentage ranged from15.49% in 0.9 FC–FC to 17.31% in 0.5 FC–0.6 FC treatments. The dif-ferences of DM percentage on soil moisture levels were significantonly between severe water deficit stress and other water deficitstress conditions.

Fig. 3. Tuber yield in relation to combined soil moisture and Zn treatments (n = 9).

R. Motalebifard et al. / Scientia Hor

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ig. 4. Tuber yield in relation to different soil moisture and P treatments (n = 9).

22.3 g L−1) was obtained under severe water deficit stress condi-ions, although WUE increased 20 and 23 percent under moderateater deficit and full-irrigated conditions, respectively (Table 3).

he differences between higher levels of soil moisture were notignificant on WUE. Application of P affected WUE of potato at 0.07robability level (Table 3) and linear increase of WUE resulted bypplication of P. The highest and lowest WUE were resulted fromhe without P and application of 60 mg P per kg of soil, respectively.

. Discussion

Water deficit reduced soil water flux from soil to root surfacend therefore LWP was decreased and resulted in lower SC (Table 4)s Atkinson et al. (2000) indicated. There were a positive correla-ion between SC and LWP in our study (r = 0.905**). In addition,ater deficit could decrease availability and uptake of cations such

s potassium and magnesium (Yuncai and Schmidhalter, 2005) thatnvolved in osmoregulation and LWP (Rao and Rao, 1983; Rao et al.,987). Lower assimilate production (lower yield in Figs. 3 and 4nd stem length in Table 3) in water deficit conditions exacerbatedhe effect on LWP. According to the results from this study, themmediate reduction in LWP due to water deficit stress (Fig. 1 andable 4) was in accordance with the reports from Pita et al. (2003),hu et al. (2004) and Ierna and Mauromicale (2006). The interac-ive effect of P application and 0.9 FC–FC moisture level on LWP wasontrary to that of the moderate water deficit treatments (Fig. 1). In.7 FC–0.8 FC level, application of 60 mg P per kg of soil with oppo-ite trend comparing with full irrigated conditions reduced LWP.

his might be because of higher vegetative growth, stem heightTable 3), biomass production and yield (Table 3) by application of0 mg P per kg of soil that increased water loss and reduced LWP.

able 3eans comparison of potato measured attributes under Zn, P and soil moisture main

ffects.

Factors Levels Stem height (cm) DM (%) WUE (g L−1)

Soil moisture0.9 FC–FC 42.51 a 15.5 b 27.3 a0.7 FC–0.8 FC 38.48 b 15.8 b 26.8 a0.5 FC–0.6 FC 35.42 c 17.3 a 22.3 b

Zn (mg kg−1)0 37.70 b 16.5 a 25.4 a10 37.96 b 16.3 a 24.8 a20 40.75 a 15.9 a 26.3 a

P (mg kg−1)0 34.12 c 16.3 a 24.8 a30 39.05 b 16.3 a 25.4 a60 43.25 a 16.0 a 26.3 a

M, dry matter; WUE, water use efficiency.ifferent letters in a column of each experimental factors show significant differ-nces in Duncan’s multiple range test at p ≤ 0.05.

ticulturae 162 (2013) 31–38 35

The results showed that reduction in soil moisture content andimposing water deficit decreased ET of potato plant (Table 4 andFig. 2). Due to reduced uptake and transport of nutrients (Yuncaiand Schmidhalter, 2005), stem height, DM percentage (Table 3),yield (Figs. 3 and 4) and SC (Table 4), water deficit reduced ETbecause of lower plant foliage growth and transpiration intensity(Table 4). Under full-irrigated conditions, soil can supply water ata steady rate to meet up the transpiration demand. However, asthe soil becomes dry, decrease in soil water flux from soil to rootsurface cannot satisfy the transpiration demand and ET decreasesas a result. Similar results were reported by Zhang et al. (2004).The increase of ET by P application under full irrigated condition(Fig. 2 and Table 4) was in agreement with those reported by Kunduet al. (2008). Whereas, Ebdon et al. (1999) showed that alone appli-cation of P and K had no effect on ET. They showed that shootgrowth response was highly correlated with ET response when Pfertilization was in the normal range. In our study there was a pos-itive correlation between ET and stem length (r = 0.855**) as wasobserved in Ebdon et al. (1999) research. Considering the role of Pin SC, LWP and growth of foliage and the water supplying effect onincreasing uptake and transport of nutrients, photosynthesis andSC, the combined addition of water and P to soil, increased ET con-siderably and the interaction of P × soil moisture was synergisticon ET (Fig. 2).

Application of Zn increased ET under full-irrigated conditions(Table 4). Zn had multiple roles in plant water relations and SC(Sharma et al., 1984; Khan et al., 2004). When enough water wassupplied, the application of Zn increased SC and improved waterrelation and transpiration rate and as a result ET was increased.But under severe water deficit conditions the application of Zn didnot improve water relation and ET was not changed significantly(Table 4).

Effect of soil moisture levels on reduction of tuber numbers,according to Table 4, was in agreement with those reported byMackerron and Jefferies (1986), Lynch and Tai (1988), Deblonde andLedent (2001), Lahlou et al. (2003), Erdem et al. (2006) and Wanget al. (2011) and were contrary with findings of Önder et al. (2005).Application of P increased tuber numbers significantly under mostof soil moisture conditions (Table 4). P has multiple effects on plantwater relations and productivity. Jenkins and Ali (2000) demon-strated that P application enhanced ground cover expansion (inour results it could be inferred from higher stem length and yieldby P application) during early stages of growth. Consequently, thegreater leaf area in crops receiving P represented higher advan-tage to tuber formation. According to significance effect of P onstem length (Table 3) and positive correlation between stem lengthand tuber numbers in current study (r = 0.875**), P applicationincreased tuber numbers (Table 4). Finally, Rosen and Bierman(2008) offered that many of hormonal and environmental factorscould influence tuber initiation. The results showed that 10 mgZn fertilizer per kg of soil affected tuber numbers significantly(Table 4). Zn plays important role in photosynthesis, protein andcarbohydrates metabolism and starch formation by activation ofmetallo-enzymes (Alloway, 2008). Zn is required for synthesis ofthe growth hormone IAA (Marschner, 1995) and tuber initiationis provoked by mentioned hormone (Kloosterman et al., 2006).Reduction of the tuber numbers in some conditions of higher Znlevels (Table 4) was in disagreement with results of Sharma et al.(1988) and could be due to P and Zn interaction. Higher level ofZn might interact with uptake of P (Soltanpour, 1969; Oroji andGolchin, 2012) or other nutrients such as manganese (Barben et al.,2010b) and reduced tuber number.

The results showed that P × soil moisture interaction was syn-ergistic on tuber yield (Fig. 4). Diminishing of water availabilityin soils alleviated potato tuber yield. The higher tuber yield infull-irrigated conditions could be attributed to different factors.

36 R. Motalebifard et al. / Scientia Horticulturae 162 (2013) 31–38

Table 4Means comparisons for potato attributes under Zn × P × soil moisture interaction effects.

Soil moisture Zn (mg kg−1) P (mg kg−1) ET (mm) LWP (−kPa) Tuber numbers SC (cm s−1)

0.9 FC–FC

0 0 88.4 de 662 f–i 3.67 gh 0.48 f–k30 112.9 bc 652 g–j 6.67 abc 0.73 c-f60 113.8 bc 456 kl 7.00 ab 1.01 b

10 0 99.0 cd 649 g–j 7.67 a 0.75 cde30 110.2 c 423 l 4.33 e–h 0.92 bcd60 137.3 a 577 h–l 7.67 a 0.95 bc

20 0 84.5 def 746 e–h 3.67 gh 0.73 c–f30 128.8 ab 252 m 5.67 b–f 1.30 a60 133.0 a 467 jkl 5.67 b–f 0.95 bc

0.7 FC–0.8 FC

0 0 50.8 hij 783 d–g 5.33 b–g 0.63 e–i30 76.7 ef 786 d–g 4.67 d–h 0.62 e–i60 82.4 def 846 c–f 5.33 b–g 0.63 e–i

10 0 52.0 ghi 623 g–k 5.67 b–f 0.67 d–g30 69.6 fg 918 a–e 7.67 a 0.54 e–j60 76.9 ef 945 a–d 6.67 abc 0.49 e–k

20 0 67.4 fgh 853 cde 4.67 d–h 0.65 e–h30 65.8 fgh 526 i–l 5.00 c–h 0.94 bc60 67.8 fgh 916 a–e 6.00 a–e 0.46 g–k

0.5 FC–0.6 FC

0 0 23.2 k 977 a–d 3.33 h 0.32 jk30 32.0 k 1038 abc 5.33 b–g 0.38 ijk60 33.2 jk 975 a–d 6.33 a–d 0.39 h–k

10 0 24.0 k 1051 ab 5.00 c–h 0.36 ijk30 34.1 jk 901 b–e 6.33 a–d 0.48 e–k60 34.5 jk 1073 ab 4.00 fgh 0.27 k

20 0 23.5 k 1102 a 4.00 fgh 0.24 k30 27.6 k 1067 ab 5.67 b–f 0.28 jk60 31.2 k 954 a–d 5.00 c–h 0.37 ijk

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T: crop evapotranspiration; LWP: leaf water potential; SC: stomatal conductance.ifferent letters in a column of each experimental factors show significant differen

irstly, this might be due to the higher SC (Table 4) and plantoliage (Table 3) that is essential for intercepting the radiation, sohat more photosynthates are produced and allocated to the tubersWestigate and Grant, 1989; Shilpi and Tuteja, 2005; Germ et al.,007). Secondly, water deficit reduces mineralization, availabilitynd supplying of nutrients especially N, P and K which leads toower uptake of these nutrients (Havlin et al., 2006). Reduction ofield with water deficit imposing was in accordance with those ofabeiro et al. (2001), Ahmadi et al. (2010) and Wang et al. (2011).he results also showed that application of P fertilizer increasedhe tuber yield especially under full irrigated conditions (Fig. 4).pplication of P increased leaf and stem length (Table 3) and SC

Table 4) that resulted in better photosynthesis, wider root sys-em (data not shown) and as a result higher tuber yield (Fig. 4). Theffect of P fertilizer on the tuber yield under full irrigated conditionsas in agreement with those reported by Chaverri and Bornemisza

1977), Rosen and Bierman (2008) and Fleisher et al. (2012b). Theon-significant effect of P on tuber yield under water deficit stressonditions was in against with results reported by Premachandrat al. (1990) and Saneoka et al. (1990). Beside non-significant effectf P fertilizer on the potato yield under water deficit conditions, itas increased linearly by P application. There were significant lin-

ar relationships between P application (P) level and the tuber yieldY) under moderate water deficit conditions (Y = 1.2883P + 329.63,

= 0.999**) and sever water deficit conditions (Y = 0.7267P + 223.13, = 0.987*). According to Figs. 1 and 2 in severe water deficit condi-ions, application of P could not mitigate water stress on LWP andT. This showed that in potato production, water supply was mainnd dominant factor and when water was limited other nutritionalactors could not affect clearly potato yield. When water was avail-ble in sufficient quantities, factors such as P and other nutrientsndicates their role better.

Fig. 3 showed that there was a significant linear relation-hip between Zn application (Zn) and the tuber yield (Y) underull-irrigated conditions (Y = 3.03Zn + 438.87, r = 0.959*). So, appli-ation of Zn increased tuber yield under higher water supplying

Duncan’s multiple range test at p ≤ 0.05.

conditions. Under moderate water stress conditions (Fig. 3), thetuber yield was increased by Zn supplying from 10 to 20 mg Zn perkg of soil. The increase of tuber yield by Zn supplying might be dueto its important roles in permeability of biomembranes (Cakmak,2000), detoxicification of ROS, plant water relations and SC (Sharmaet al., 1984; Khan et al., 2004). The same results were reportedby Bagci et al. (2007), Wang (2009) and Oroji and Golchin (2012).Results showed that there was no negative or positive interactionbetween Zn and P on tuber yield. While Soltanpour (1969), Chaverriand Bornemisza (1977), Barben et al. (2010a) showed that Zn andP had negative interaction on yield and uptake of nutrients. ButTrehan and Grewal (1983) showed that balanced application of Pand Zn could increase yield by translocation of assimilates fromshoot to tubers.

As showed in Table 3, WUE reduced by declining of water sup-ply. Considering the same values of WUE for both treatments of 0.9FC–FC and 0.7 FC–0.8 FC (Table 3), it could be possible to maintainrelatively high yield and optimal WUE by selecting proper irrigationregime. There were various reasons for higher reduction of WUEin severe water deficit conditions (Table 3): Firstly, tuber yield in0.5 FC–0.6 FC treatment sharply reduced comparing to total waterconsumption; Secondly, in determining the potato tuber yield, animportant role is played by the efficacy (rate and length) of thecarbohydrate translocation from leaves to storage tubers (Iernaand Mauromicale, 2006) and water deficit conditions may affecttranslocation of carbohydrates. Our results showed that harvestindex of potato decreased significantly by water deficit and higherharvest index (69.6%) observed in 0.9 FC–FC level that decreased21% in 0.5 FC–0.6 FC moisture level. This result showed that translo-cation of carbohydrates was affected by water deficit. The effectof water deficit stress on the harvest index depended on varietyof potato (Tourneux et al., 2003) and time of harvest (Dalla Costa

et al., 1997) in some cases the harvest index was increased by waterdeficit imposing or was not changed (Dalla Costa et al., 1997). Effectof water supply on WUE was in agreement with results from Önderet al. (2005), Erdem et al. (2006) and Ayas and Korukc u (2010) and

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as in contrary to results of Yuan et al. (2003) and Qiu et al. (2008)nd in disagreement with finding of Fleisher et al. (2008) results.UE was linearly increased by application of P fertilizer (Table 3)

nd this increase was significant at 0.07 probability level. P fertil-zer increased root growth (Pathuluri et al., 1986) and supportedhe response of plant to water deficit stress due to its effect on sto-

atal behavior and resistance to water flow within the plant (Gargt al., 2004), although, the effect of P on photosynthesis, suitablenergy transportation and biomass production resulted in higherield and as a result WUE (Marschner, 1995).

Type of soil that used in this project can affect the results. So,e presented soil physical and chemical properties in Table 1. The

ffects of soil moisture regime, P and Zn on measured parametersould be influenced by soil type. ET and LWP were affected mostlyy water availability and the type of soil could not influenced resultsecause of pots weighting two times per day. DM and tuber num-ers were mostly affected by type of cultivar and water deficit stressnd the soil effect was negligible on these. WUE and especially yieldould be affected by soil characteristics.

. Conclusion

The results showed that the main effects of P, Zn and soil mois-ure were significant on the ET, tuber numbers, yield and WUE.pplication of P improved ET, tuber numbers, tuber yield, and WUE,hile water deficit stress reduced the mentioned attributes. Effect

f Zn levels was significant only on tuber number. Two way inter-ctions of P, Zn and soil moisture were mainly synergistic on ET,uber number, tuber yield and LWP. However, in some cases, theype of interaction depended on the levels of factors. The adverseffects of water deficit stress on potato growth and physiologicalttributes such as LWP, ET, tuber number, yield and WUE could bemeliorated by nutrients (especially P) supply. The results showedhat P requirement enhanced by increasing water deficit. In gen-ral, to achieve the optimum potato tuber yield in similar soils,pplication of 10 mg Zn and 30 mg P per kg of dry soil could be rec-mmended under full-irrigated conditions. Because of no scoped Pevel under water deficit stress conditions, the yield of potato coulde calculated from Y = 1.2883P + 329.63 regression equation underoderate water deficit conditions and from Y = 0.7267P + 223.13

egression equation under sever water deficit conditions at P stud-ed levels range.

cknowledgements

The authors would like to thank Vice Chancellor for Research andechnology University of Tabriz for financial support of this projecthat this paper includes results of mentioned project. We are alsorateful to the reviewers for perceptive comments and correctionsn the manuscript.

eferences

hmadi, S.H., Andersen, M.N., Plauborg, F., Poulsen, R.T., Jensen, C.R., Sepaskhah,A.R., Hansen, S., 2010. Effects of irrigation strategies and soils on field grownpotatoes: yield and water productivity. Agric. Water Manag. 97, 1923–1930.

lloway, B.J., 2008. Zinc in Soils and Crop Nutrition, 2nd ed. IZA and IFA, France.tkinson, C.J., Policarpo, M., Webster, A.D., Kingswell, G., 2000. Drought tolerance of

clonal Malus determined from measurements of stomatal conductance and leafwater potential. Tree Physiol. 20, 557–563.

yas, S., Korukc u, A., 2010. Water-yield relationships in deficit irrigated potato. J.Agric. Fac. Uludag Univ. 24 (2), 23–36.

agci, S.A., Ekiz, H., Yilmaz, A., Cakmak, I., 2007. Effects of zinc deficiency and drought

on grain yield of field-grown wheat cultivars in central Anatolia. J. Agron. CropSci. 193, 198–206.

arben, S.A., Hopkins, B.G., Jolley, V.D., Webb, B.L., Nicholas, B.A., 2010a. Phosphorusand zinc interactions in chelator-buffered solution grown russet Burbank potato.J. Plant Nutr. 33, 587–601.

ticulturae 162 (2013) 31–38 37

Barben, S.A., Hopkins, B.G., Jolley, V.D., Webb, B.L., Nicholas, B.A., 2010b. Phosphorusand manganese interactions and their relationships with zinc in chelator-buffered solution grown russet Burbank potato. J. Plant Nutr. 33, 752–769.

Cakmak, I., 2000. Possible roles of zinc in protecting plant cells from damage byreactive oxygen species. New Phytol. 146, 185–205.

Chaverri, B.A., Bornemisza, E., 1977. Phosphorus–zinc interactions in the potato(Solanum tuberosum L.) crop in the Pacayas area. Agronomía Costarric. 1 (2),83–92.

Dalla Costa, L., Delle Vedove, G., Gianquinto, G., Giovanardi, R., Peressotti, A., 1997.Yield, water use efficiency and nitrogen uptake in potato: influence of droughtstress. Potato Res. 40, 19–34.

Deblonde, P.M.K., Ledent, J.F., 2001. Effects of moderate drought conditions on greenleaf number stem height, leaf length and tuber yield of potato cultivars. Eur. J.Agron. 14, 31–41.

Ebdon, J., Petrovic, White, R.A., 1999. Interaction of nitrogen, phosphorus, and potas-sium on evapotranspiration rate and growth of Kentucky bluegrass. Crop Sci. 39,209–218.

Erdem, T., Erdem, Y., Orta, H., Okursoy, H., 2006. Water yield relationships of potatounder different irrigation methods and regimens. Sci. Agric. 63 (3), 226–231.

Fabeiro, C., Olalla, F.M.O., Juan, J.A., 2001. Yield and size of deficit irrigated potatoes.Agric. Water Manag. 48, 255–266.

FAO, 2007. FAOSTAT. Food and Agriculture Organization of the United Nations. Avail-able in: http://faostat.fao.org/statistics

FAO, 2010. FAOSTAT. Food and Agriculture Organization of the United Nations. Avail-able in: http://faostat.fao.org/countryprofiles/

Fleisher, D.H., Timlin, D.J., Reddy, V.R., 2008. Interactive effects of carbon dioxide andwater stress on potato canopy growth and development. Agron. J. 100, 711–719.

Fleisher, D.H., Barnaby, J., Sicher, R., Resop, J.P., Timlin, D.J., Reddy, V.R., 2012a. Effectsof elevated CO2 and cyclic drought on potato under varying radiation regimes.Agric. Forest Meteorol. 171-172, 270–280.

Fleisher, D.H., Wang, Q., Timlin, D.J., Chun, J.A., Reddy, V.R., 2012b. Response of potatogas exchange and productivity to phosphorus deficiency and carbon dioxideenrichment. Crop Sci. 52, 1803–1815.

Garg, B.K., Burman, U., Kathju, S., 2004. The influence of phosphorus nutrition on thephysiological response of moth bean genotype to drought. J. Plant Nutr. Soil Sci.167, 503–508.

Gee, G.W., Bauder, J.W.C., 1986. Methods of Soil Analysis. Part1. Physical and Min-eralogical Methods, 2nd ed. American Society of Agronomy, USA.

Germ, M., Kreft, I., Stibilj, V., Urbanc-Bercic, O., 2007. Combined effects of seleniumand drought on photosynthesis and mitochondrial respiration in potato. PlantPhysiol. Biochem. 45, 162–167.

Havlin, J.L., Beaton, J.D., Tisdale, S.L., Nelson, W.L., 2006. Soil Fertility and Fertilizersan Introduction to Nutrient Management, 7th ed. Prentice Hall of India, NewDelhi, India.

Howell, T.A., Yazar, A., Schneıder, A.D., Dusek, D.A., Copeland, K.S., 1995. Yield andwater use efficiency of corn in response to LEPA irrigation. Trans. ASAE 38 (6),1737–1747.

Jefferies, R.A., 1995. Physiology of crop response to drought. In: Haverkort, A.J.,MacKerron, D.K.L. (Eds.), Potato Ecology and Modeling of Crops under ConditionsLimiting Growth. Kluwer Academic Publishers, Dordrecht, pp. 61–74.

Jenkins, P.D., Ali, H., 2000. Phosphate supply and progeny tuber numbers in potatocrops. Annu. Appl. Biol. 136, 41–46.

Ierna, A., Pandino, G., Lombardo, S., Mauromicale, G., 2011. Tuber yield, water andfertilizer productivity in early potato as affected by a combination of irrigationand fertilization. Agric. Water Manag. 101, 35–41.

Ierna, A., Mauromicale, G., 2006. Physiological and growth response to moderatewater deficit of off-season potatoes in a Mediterranean environment. Agric.Water Manag. 82, 193–209.

Ierna, A., Mauromicale, G., 2012. Tuber yield and irrigation water productivityin early potatoes as affected by irrigation regime. Agric. Water Manag. 115,276–284.

Khan, H.R., McDonald, G.K., Rengel, Z., 2004. Zinc fertilization and water stress affectsplant water relations, stomatal conductance and osmotic adjustment in chickpea(Cicer arientinum L.). Plant Soil 267, 271–284.

Kirkham, M.B., 2004. Principles of Soil and Plant Water Relations. Elsevier AcademicPress Publications, USA.

Kloosterman, B., Visser, R.G., Bachmen, C.W., 2006. Isolation and characterizationof a novel potato auxin/indole-3-acetic acid family member (StIAA2) that isinvolved in petiole hyponasty and shoot morphogenesis. Plant Physiol. Biochem.44 (11–12), 766–775.

Kundu, M., Chakraborty, P.K., Mukherjee, A., Sarkar, S., 2008. Influence of irrigationfrequencies and phosphate fertilization on actual evapotranspiration rate, yieldand water use pattern of rajmash (Phaseolus vulgaris L.). Agric. Water Manag. 95,383–390.

Lahlou, O., Ouattar, S., Ledent, J.F., 2003. The effect of drought and cultivar ongrowth parameters, yield and yield components of potato. Agronomie 23 (3),257–268.

Lynch, D.R., Tai, G.C.C., 1988. Yield and yield component response of eight potatogenotypes to water stress. Crop Sci. 29 (5), 1207–1211.

Mackerron, D.K.L., Jefferies, R.A., 1986. The influence of early soil moisture stress ontuber numbers in potato. Potato Res. 29 (3), 299–312.

Marschner, H., 1995. Mineral Nutrition of Higher Plants, 2nd ed. Academic Press,USA.

Önder, S., C alıs kan, M.E., Önder, D., C alıs kan, S., 2005. Different irrigation methodsand water stress effects on potato yield and yield components. Agric. WaterManag. 73, 73–86.

3 ia Hor

O

P

P

P

R

R

R

R

S

S

S

S

S

S

S

S

S

S

8 R. Motalebifard et al. / Scient

roji, H., Golchin, A., 2012. The effect of zinc, manganese and copper on potatoyield and tuber concentration of phosphorus and iron. J. Sci. Technol. Agric. Nat.Resour. 16, 221–230.

athuluri, J.V., Kissel, D.V., Whitney, D.A., Theim, S.J., 1986. Phosphorus uptake fromsoil layers having different soil test phosphorus levels. Agron. J. 78 (6), 991–994.

ita, P., Gascó, A., Pardos, J.A., 2003. Xylem cavitation, leaf growth and leaf waterpotential in Eucalyptus globulus clones under well-watered and drought condi-tions. Funct. Plant Biol. 30 (8), 891–899.

remachandra, G.S., Saneoka, H., Fujita, K., Ogata, S., 1990. Cell membrane stabilityand leaf water relation as affected by phosphorus nutrition under water stressin maize. Soil Sci. Plant Nutr. 36 (4), 653–659.

ao, I.M., Sharp, R.E., Boyer, J.S., 1987. Leaf magnesium alters photosyntheticresponse to low water potentials in sunflower. Plant Physiol. 84, 1214–1219.

ao, K.V., Rao, K.V.M., 1983. Influence of potassium nutrition on stomatal behaviour,transpiration rate and leaf water potential of pigeon pea (Cajanus cajan (L.)Millsp.) in sand culture. Proc.: Plant Sci. 92 (4), 323–330.

eddy, A.R., Chaitanya, K.V., Vivekanandan, M., 2004. Drought-induced responsesof photosynthesis and antioxidant metabolism in higher plants. J. Plant Physiol.161, 1189–1202.

osen, C.J., Bierman, P.M., 2008. Potato yield and tuber set as affected by phosphorusfertilization. Am. J. Potato Res. 85, 110–120.

ohota, T., 1985. Phosphorus and zinc application in potato at Shillong. J. IndianPotato Assoc. 12, 95–97.

aneoka, H., Fujita, K., Ogata, S., 1990. Effect of phosphorus on drought tolerance inChloris gayana Kunth and Coix lacryma-jobi L. Soil Sci. Plant Nutr. 36 (2), 267–274.

ardans, J., Penuelas, J., 2005. Drought decreases soil enzyme activity in a Mediter-ranean Quercus ilex L. forest. Soil Biol. Biochem. 37 (3), 455–461.

ardans, J., Penuelas, J., 2007. Drought changes phosphorus and potassium accumu-lation patterns in an evergreen Mediterranean forest. Funct. Ecol. 21, 191–201.

ardans, J., Penuelas, J., Estiarte, M., 2006. Warming and drought alter soil phos-phatase activity and soil P availability in a Mediterranean shrubland. Plant Soil289, 227–238.

halhevet, J., Shimshi, D., Meir, T., 1983. Potato irrigation requirements in a hotclimate using sprinkler and drip methods. Agron. J. 75, 13–16.

harma, U.C., Grewal, J.S., Trehan, S.P., 1988. Response of potato to applied zinc onsoils with variable zinc availability. Potato J. 15 (1 and 2), 21–26.

harma, C.P., Mehrotra, S.C., Sharma, P.N., Bisht, S.S., 1984. Water stress induced by

zinc deficiency in cabbage. Curr. Sci. 53, 44–45.

hilpi, M., Tuteja, N., 2005. Cold, salinity and drought stresses: an overview. Arch.Biochem. Biophys. 444, 139–158.

oltanpour, P.N., 1969. Effect of N, P and Zn placement on yield and composition ofpotatoes. Agron. J. 61, 288–289.

ticulturae 162 (2013) 31–38

Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N., Tabatabaei,M.A., Johnson, C.T., Sumner, M.E., 1996. Methods of Soil Analysis. Part 3, ChemicalMethods. Soil Science Society of American Book Ser. 5. SSSA, Madison, WI, USA.

Tekalign, T., Hammes, P.S., 2005. Growth and productivity of potato as influenced bycultivar and reproductive growth. II. Growth analysis, tuber yield and quality.Sci. Hort. 105, 29–44.

Tourneux, C., Devaux, A., Camacho, M.R., Mamani, P., Ledent, J.F., 2003. Effects ofwater shortage on six potato genotypes in the highlands of Bolivia (I): morpho-logical parameters, growth and yield. Agronomie 23 (2), 169–179.

Trehan, S., Grewal, J., 1983. Zinc–phosphorus interaction in potato. Indian J. Ecol. 10(2), 215–222.

Trehan, S.P., Sharma, R.C., 2000. Phosphorus and zinc uptake efficiency of potato(Solanum tuberosum) in comparison to wheat (Triticum aestivum), maize (Zeamays) and sunflower (Helianthus annuus). Indian J. Agric. Sci. 70, 840–845.

Qiu, G.Y., Wang, L., He, X., Zhang, X., Chen, S., Chen, J., Yang, Y., 2008. Wateruse efficiency and evapotranspiration of winter wheat and its responseto irrigation regime in the north China plain. Agric. Forest Meteorol. 148,1848–1859.

Wang, H., Liu, R.L., Jin, J.Y., 2009. Effects of zinc and soil moisture on photosyntheticrate and chlorophyll fluorescence parameters of maize. Biologia Plant. 53 (1),191–194.

Wang, F.X., Wu, X.X., Shock, C.C., Chu, L.Y., Gu, X.X., Xue, X., 2011. Effects of dripirrigation regimes on potato tuber yield and quality under plastic mulch in aridNorthwestern China. Field Crops Res. 122, 78–84.

Welch, R.M., Webb, M.J., Loneragan, J.F., 1982. Zinc in membrane function and itsrole in phosphorus toxicity. In: Scaife, A. (Ed.), Proceedings of the Ninth PlantNutrition Colloquium. CAB International, Warwick, UK; Wallingford, UK, pp.710–715.

Westigate, M.E., Grant, D.T., 1989. Effect of water deficits on seed development insoybean. I. Tissue water status. Plant Physiol. 91, 975–979.

Yuan, B.Z., Nishiyama, S., Kang, Y., 2003. Effects of different irrigation regimeson the growth and yield of drip irrigated potato. Agric. Water Manag. 63,153–167.

Yuncai, H., Schmidhalter, U., 2005. Drought and salinity: a comparison oftheir effects on mineral nutrition of plants. J. Plant Nutr. Soil Sci. 168,541–549.

Zhang, Z., Kendy, E., Qiang, Y., Changming, L., Yanjun, S., Hongyong, S., 2004. Effect

of soil water deficit on evapotranspiration, crop yield, and water use efficiencyin the north China plain. Agric. Water Manag. 64, 107–122.

Zhu, L.H., Peppel, A.V.D., Li, X.Y., Welander, M., 2004. Changes of leaf water poten-tial and endogenous cytokinins in young apple trees treated with or withoutpaclobutrazol under drought conditions. Sci. Hort. 99, 133–141.