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Effects of Irrigation andNitrogen Rates on Growth,Yield, and Quality ofMuskmelon in Semiarid RegionsHalil Kirnak a , David Higgs b , Cengiz Kaya c & IsmailTas aa Irrigation Department, Agriculture Faculty,University of Harran , Sanliurfa, Turkeyb Environmental Sciences, University ofHertfordshire , Hatfield, Hertsfordshire, UnitedKingdomc Soil Science and Plant Nutrition Department,Agriculture Faculty, University of Harran , Sanliurfa,TurkeyPublished online: 14 Feb 2007.

To cite this article: Halil Kirnak , David Higgs , Cengiz Kaya & Ismail Tas (2005)Effects of Irrigation and Nitrogen Rates on Growth, Yield, and Quality of Muskmelonin Semiarid Regions, Journal of Plant Nutrition, 28:4, 621-638, DOI: 10.1081/PLN-200052635

To link to this article: http://dx.doi.org/10.1081/PLN-200052635

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Journal of Plant Nutrition, 28: 621–638, 2005

Copyright © Taylor & Francis Inc.

ISSN: 0190-4167 print / 1532-4087 online

DOI: 10.1081/PLN-200052635

Effects of Irrigation and Nitrogen Rates onGrowth, Yield, and Quality of Muskmelon

in Semiarid Regions

Halil Kirnak,1 David Higgs,2 Cengiz Kaya,3 and Ismail Tas1

1Irrigation Department, Agriculture Faculty, University of Harran, Sanliurfa, Turkey2Environmental Sciences, University of Hertfordshire, Hatfield, Hertsfordshire,

United Kingdom3Soil Science and Plant Nutrition Department, Agriculture Faculty, University

of Harran, Sanliurfa, Turkey

ABSTRACT

Muskmelon (Cucumis melo L. cv. ‘Polidor’) were grown under field conditions to in-vestigate the effects of different nitrogen (N) levels (0, 40, 80, and 120 kg ha−1) on plantgrowth, water use efficiency, fruit yield and quality (weight, sizes, and water-solubledry matter), leaf relative water content, and macro nutrition under three different ir-rigation regimes. Irrigation was applied based on cumulative class A pan evaporation(Ep). Plant treatments were as follows: (1) well-watered treatment (C) received 100%replenishment of Ep on a daily basis, (2) water-stressed treatment (WS) received 75%replenishment of Ep at three-day intervals, and (3) severely water-stressed (SWS): treat-ment received 50% replenishment of Ep at six- day intervals. Plants grown under Cat 120 kg N ha−1 produced significantly higher biomass (175.6 g plant−1), fruit yield(36.05 t ha−1), fruit weight (2.25 kg fruit−1), and leaf relative water content (93.5%)under increasing N levels than did the two deficit irrigation treatments. The WS or SWStreatments caused reductions in all parameters measured except water-soluble dry matter(SDM) concentrations in fruits compared with those receiving unstressed (C) treatment.The WS irrigation regime with 80 kg ha−1 N significantly improved the fruit yield andsize, plant dry matter, leaf area, and IWUE compared with the SWS regime. IncreasedN significantly enhanced foliar N in the unstressed plants. Increasing N rate in the SWStreatment did not increase fruit yield with the same trend found in the WS and C treat-ments with increasing N levels. The yield reduction under severe water shortage wasmuch more severe at high N rates. Water use (ET) at the C treatment at 120 kg ha−1 N

Received 29 May 2003; accepted 21 May 2004.Address correspondence to Halil Kirnak, Irrigation Department, Agriculture Faculty,

University of Harran, 63200 Sanliurfa, Turkey. E-mail: hkirnak@yahoo.com

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622 H. Kirnak et al.

ranged between 160 and 165 cm, while SWS reduced ET to 90 cm at 0 and 40 kg ha−1 N.Nitrogen supply modified water use at C and WS irrigation regimes. Muskmelon yieldresponse to N rate was quadratic and differed with the level of irrigation. This moderatewater deficit (SW) may be an alternative irrigation choice with a suitable N applicationrate for muskmelon growers in arid and semi-arid regions if the goal is to irrigate an agri-cultural area with limited water supply for more growers, but not if it is maximizing eco-nomic yield. Growers should accept a significant yield reduction in exchange for waterconservation.

Keywords: water deficit, Cucumis melo L., trickle irrigation, water stress, nitrogen

INTRODUCTION

Muskmelon is an important summer crop grown in the Mediterranean regionthat requires irrigation to achieve optimal yield and quality. Most producers inthis region use surface irrigation, which often results in both waste of waterand loss of nutrients (Clark et al., 1996; Bogle and Hartz, 1986). When en-vironmental factors are otherwise favorable, vegetable growth and yields areoften reduced if irrigation frequency is inadequate. The muskmelon crop hascritical periods of growth when irrigation is a necessity for optimal yield andquality (Hartz, 1997; Hardeman et al., 1999). However, water is a limited andexpensive commodity in many production areas (particularly when applied byinefficient surface irrigation methods) and water shortages frequently occur atcritical times.

Irrigation and nitroge (N) fertilization are two important aspects ofmuskmelon production. Most researchers have been focused on schedulingdeficit irrigation along with determining a suitable N rate to conserve water andthe environment while maintaining crop productivity (Pandey et al., 2000). Pewand Gardner (1983) found that heavy furrow irrigation decreased yield and fruitwater-soluble dry matter (SDM) while increasing cull rate in muskmelon. Bhella(1985) reported that drip irrigation increased muskmelon yield and fruit quality,but reduced SDM, when compared with no irrigation. Leib et al. (2000) recom-mended use of mulch for muskmelon production, because yield of muskmelonwas higher under plastic mulch on raised beds compared with its performanceunder no mulch treatments.

Few reports have been published on the effects of combining different dripirrigation regimes with varying N application rates on the yield and qualityin muskmelon. Consequently, links between irrigation, N fertilization, growth,and fruit yield are not well established. In this study, a field experiment withone commercial muskmelon cultivar, ‘Polidor’, was carried out to study thejoint effects of water stress and N rates on plant growth, yield parameters, andwater use efficiency.

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Effects of Irrigation and Nitrogen Rates on Growth 623

MATERIALS AND METHODS

Plant Culture, Treatments, and Irrigation

The experiment was carried out on a clay loam soil, classified as an Ikizce soilseries (Vertic Calciorthid aridisol), from May to August 2000 and 2001 at theAgriculture Research Station of the University of Harran in Sanliurfa, Turkey.The altitude, latitude, and longitude of the experimental site are 465 m, 37◦08′

N, and 38◦46′ E, respectively. Table 1 summarizes the monthly climate datacompared with the long-term mean climatic data. The 0–60 cm depth of soilprofile had a dry bulk density of 1.32 g/cm3, pH of 7.1, and EC of 1.10 dS/m.The field capacity (FC) was 32.50%, and the permanent wilting point (PWP)21.60%, as determined gravimetrically. The N content of the soil at the site for0–40 cm soil depth was 40 kg ha−1. Irrigation water was of good quality, withECw of 0.48 dS/m, containing (meq/L) 1.1 Ca2+, 1.0 Mg2+, 0.25 Na+, 0.02 K+,0.75 SO2−

4 , 0.90 HCO−3 , 0.60 Cl−, and a pH of 7.0.

‘Polidor,’ a hybrid cultivar of muskmelon widely cultivated in southeastTurkey, was selected for study. In both years, seeds were germinated in fine sand

Table 1Historical monthly and growing season climatic data of the experimental area

Climatic parameters April May June July August

Long-term (means, 1929–1999)Minimum air temperature (◦C) −3.4 1.0 9.4 11.0 9.2Maximum air temperature (◦C) 34.8 43.0 45.4 46.8 46.6Average temperature (◦C) 15.2 21.4 28.0 31.4 30.4Rainfall (mm) 25.4 25.6 4.8 0.1 —Relative humidity (%) 54 42 35 33 36Wind speed (m/s) 1.6 1.9 2.5 2.6 2.1

Growing season (2000)Minimum air temperature (◦C) 7.4 9.3 17.2 22.2 21.1Maximum air temperature (◦C) 31.6 35.8 40.4 44.0 42.4Average temperature (◦C) 17.2 20.1 29.2 32.8 33.1Rainfall (mm) 59.9 0.6 — — —Relative humidity (%) 60.6 52.8 28.7 32.9 41.9Wind speed (m/s) 2.4 2.3 3.0 2.8 2.7

Growing season (2001)Minimum air temperature (◦C) 7.6 9.6 18.0 22.8 21.5Maximum air temperature (◦C) 32.1 36.9 41.1 44.3 42.9Average temperature (◦C) 17.8 20.6 30.1 33.2 33.5Rainfall (mm) 58.4 0.2 — — —Relative humidity (%) 60.9 53.4 29.4 33.6 42.1Wind speed (m/s) 2.3 2.4 3.1 2.9 3.0

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Figure 1. Experimental layout.

during the second week of March and at the second true leaf stage (25 d), andsimilar-sized seedlings were transplanted into plastic tubs containing previouslywashed sand. Similar sized seedlings were again selected at the fourth trueleaf stage (20 d) and transplanted to the field in the first week of May. Theplants were drip irrigated from 10 a.m. to 5 p.m. at 4 L h−1 m−1 for a weekto promote root establishment without stress and to cool the air against highambient temperatures during the daytime periods.

All raised beds were covered with a black polyethylene mulch 100 µm inthickness (Verim Plastic Co., Turkey). The raised field beds, 10.0 m long and1.25 m wide, were prepared to a height of 0.20 m. Twenty plants per replicatewere planted in rows with an inter-plant spacing of 0.5 m and an inter-rowspacing of 2 m. A single drip irrigation tube (Goktepe Co., Izmir, Turkey), with2.0 L/h and 0.5 m emitter spacing, was placed in the center of each raised bedsurface. Figure 1 shows the experimental layout. The operating pressure of thedrip irrigation system was constant during the experiment as 100 kPa. Eachplot had a separate flow meter (Teksan Co., Turkey) to monitor water input. Norainfall was recorded during the experimental period.

Plant treatments were as follows: (1) Well-watered treatmen (C) received100% replenishment of Ep on a daily basis, (2) water-stressed treatment (WS)received 75% replenishment of Ep at three-day intervals and (3) severely water-stressed treatment (SWS) received 50% replenishment of Ep at six-day intervals.Four different N levels (0,40, 80, and 120 kg ha−1) were combined with theabove treatments. Based on soil test results, all treatments received the sametotal amounts of Phosphorus (P) (24 kg ha−1) and potassium (K) (73 kg ha−1)fertilizer for the season. Forty percent of the N and K fertilizer was surfaceapplied and all the P was banded into the soil prior to planting. The remaining60% of N and K was injected weekly through the drip irrigation system startingtwo weeks after transplanting until two weeks before the last harvest. Nitrogen,P, and K were applied as ammonium sulphate, triple super phosphate, andpotassium sulphate respectively. A regular spray program for disease and insectcontrol was followed throughout the growing period according to standardmanagement practices. In order to prevent insect and pests infestation, a 0.3%concentration of Thiodan 35 EC (Endosulfan) and 0.05% Nuvacron 40 EC(Monochrotophos) were applied, respectively. Tachigaren 70 WP (Hymexazol)was also applied, to control soil-borne disease.

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Effects of Irrigation and Nitrogen Rates on Growth 625

Soil moisture was monitored using paired tensiometers installed at 30 and60 cm soil depths placed between two plants in rows. One paired tensiometerper replicate was installed. The evaporation data were obtained from a ClassA pan evaporimeter sited near the experimental field and were collected ona daily basis. The irrigation schedule was initiated when the percentage ofsoil cover reached 30% (approximately three weeks after transplanting at theend of May). The applied irrigation water was estimated from the product ofcumulative class A pan evaporation, plant-pan coefficient (Kcp), and percentageof soil cover (CP) (Doorenbos and Pruitt, 1992):

I = Epan × Kcp × CP

where I is applied irrigation water (mm), Epan is cumulative evaporation amountin the pre-determined irrigation intervals (mm), Kcp is crop-pan coefficient (50,75, and 100%), and CP is the percentage of soil cover.

Evapotranspiration (ET) for each treatment was calculated according tothe water balance approach (Doorenbos and Kassam, 1988):

ET = I + P − Dr − Rf ± �s

where ET is evapotranspiration, I is irrigation water applied during the growthperiod, P is effective rainfall during the growth period plus capillary rise, Dr

is amount of drainage water, Rf is amount of runoff, and �s is change in thesoil-moisture content determined by gravimetric sampling. In order to deter-mine actual ET, soil moisture content between 0 and 60 cm was measuredgravimetrically prior to each irrigation, on the 6th, 12th, 18th, 24th, and 30thday of each month, and at harvest. Since there was no observed runoff duringthe experiment and the water table was in 4 m depth, capillary flow to rootzone and runoff flow were assumed to be negligible in the calculation of ET.Drainage below 60 cm, after a number of soil-water content measurements,was considered to be negligible. So the above equation was simplified to ET =I + P ± �s.

Total leaf area was determined with a portable leaf area meter (LI-3100,LI-COR, Lincoln, NE) at the beginning of the fruit formation period. Fruitswere harvested when fully mature during July and August. The first harvestwas carried out in the second week of July and repeated three times (dependingon fruit ripeness) until the end of August.

Dry Weight Determination and Chemical Analysis

Total dry-matter accumulation was estimated using four plants from each repli-cate. For this purpose, whole plants (without fruit) at the end of the experimentwere used. Leaves, roots, and stems were separated and weighed to obtain root

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626 H. Kirnak et al.

and shoot (leaves + stem) dry weight after drying them at 70◦C for 48 h toconstant weight.

Leaf samples from five plants were collected after the last fruit harvestand analyzed for leaf N, K, P. For chemical analysis, leaves were washed in 2%phosphate-free, mild detergent solution (La2, Klarett) to remove any dust on leafsurfaces, soaked in 0.5 M HCl for 20 seconds followed by three rinses in distilledwater, and then dried at 70◦C for 48 h to constant weight. Dried leaves wereground to powder using a mortar and pestle and stored in polyethylene bottles.Ground samples (ca. 0.5 g per replicate) were ashed at 550◦C for six hours. Thewhite ash was recovered in 2 M hot HCl, filtered into a 50 mL volumetric flask inwhich volume was then adjusted to 50 mL using distilled water. Potassium and Pwere determined in these sample solutions. Nitrogen was determined in samplesof 0.1 g dry weight using the Kjeldahl method. Phosphorus was analyzed by thevanadate-molybdate method using a UV/visible spectrophotometer (Bausch &Lomb, Belgium) at 470 nm wavelength. potassium in the sample solution wasanalyzed using a flame photometer (Corning 400, UK) (Chapman and Pratt,1982).

Leaf Relative Water Content

Leaf relative water content (LRWC) was calculated based on the methods ofYamasaki and Dillenburg (1999). Leaves of four randomly chosen plants perreplicate were collected from the mid-section of each plant in order to minimizeplant age effects. Individual leaves were first removed from stem and thenweighed to obtain fresh weight (FM). In order to determine the turgid weight(TM), leaves were floated in distilled water inside a closed Petri dish. Duringthe imbibition period, leaf samples were weighed periodically after the waterwas gently wiped from the leaf surface with tissue paper. At the end of theimbibition period, leaf samples were placed in a pre-heated oven at 80◦C for48 h in order to obtain dry weight (DM). All weight measurements were madeusing an analytical balance with a precision of 0.0001 g. Values of FM, TM,and DM were used to calculate LRWC using this formula:

LRWC(%) = FM − DM

TM − DM× 100

Fruit Yield, Quality, and Water Use Efficiency

Individual fruit weight, fruit sizes (fruit diameter and fruit length), and SDMwere calculated from 15 randomly chosen fruits per replicate at each harvest.The cull rate of the muskmelon (fruits lighter than 0.40 kg, rotten or withvisual defects) was also determined in order to calculate the marketable yield.

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Effects of Irrigation and Nitrogen Rates on Growth 627

Water-soluble dry matter was measured by a hand-held refractometer. Irrigationwater use efficiency (IWUE) was calculated from the marketable fruit yieldsand amount of water applied to the plants for the treatments during the grow-ing season. Total water use efficiency (TWUE) was computed as the ratio ofmarketable fruit yields to water use. Water use was the total of seasonal wa-ter depletion (planting to harvest) plus rainfall and irrigations during the sameperiod.

Statistical Analysis

A randomized split-plot design with three replications and 12 treatments wasused. Irrigation was assigned to the main plot, N levels to the subplots. Data(dry weights of root and shoot, leaf area, LRWC, fruit weights and sizes, SDM,marketable fruit yield, water use efficiencies, and macro elements in the leaves)were analyzed using a two-way ANOVA using the Minitab statistical softwarepackage (Minitab Inc., State College, PA). Treatment effects were consideredsignificant at P < 0.01.

RESULTS AND DISCUSSION

Water Consumption and Irrigation Rate

The amounts of irrigation water applied for C, WS, and SWS were 1350, 1050,and 750 mm, respectively. The seasonal water use of drip-irrigated muskmelonvaried from a low of 900 mm in SWS to a high of 1600 mm in the non-stressed treatment (C). The water conservation with WS and SWS treatmentswas 22% and 44%, respectively, compared with C treatment. The water use(ET) increased with higher N levels and under C treatment. However, increasesin water use along with higher N levels (especially from 80 to 120 kg ha−1 N)were not recorded in stressed treatments (Table 2). Figure 2 shows cumulativeevaporation data for growing seasons. The evaporation level reached its highestvalue in July and August based on climatic parameters. Water use was linearlyrelated to muskmelon yield (p < 0.05) in both years. The relationship betweenwater use and yield of muskmelon was yield = 36.618 + 3.3405 ET (R2 = 0.87)and yield = 40.876 + 3.2422 ET (R2 = 0.88) for 2000 and 2001, respectively.There was no significant difference between 2000 and 2001 in terms of wateruse. The ET value at 80 kg N ha−1 was similar to or less than that at 120 kgN ha−1 for WS and SWS treatments. The 120 kg N ha−1 produced greater ETvalue (an average of 1625 mm) under C treatment.

Tensiometers measure soil matric potential, which is an indirect measureof soil water content in the root zone. The higher the tension reading, the drier

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Tabl

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keta

ble

frui

tyi

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(MFY

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vels

(kg

ha−1

)

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2001

NM

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UE

TW

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MFY

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ET

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ls(t

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(tha

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(tha

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(tha

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(cm

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T(t

ha−1

cm−1

)(t

ha−1

cm−1

)

C0

28.8

e13

513

80.

21e

0.20

cd29

.1f

135

140

0.22

d0.

21bc

4032

.1c

135

147

0.24

d0.

22bc

33.5

c13

514

90.

25c

0.22

b80

34.8

b13

515

60.

26bc

0.22

bc35

.9b

135

160

0.27

b0.

22b

120

35.4

a13

516

00.

26bc

0.22

bc36

.7a

135

165

0.27

b0.

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WS

025

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105

110

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d0.

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25.5

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0.22

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29.9

f10

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80.

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0.25

a30

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105

120

0.29

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105

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30.5

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18.5

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Inte

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628

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Effects of Irrigation and Nitrogen Rates on Growth 629

Figure 2. Pan evaporation data for growing seasons by month and year.

the soil and the more energy the crop has to expend to continue transpiration(Hardeman et al., 1999). Average tensiometer readings ranged from –10 kPa to–22 kPa for the control, C from –45 kPa to –55 kPa for WS, and from –68 kPato –80 kPa for SWS. As application of water decreased, soil moisture tensionincreased (data not shown).

Fruit Yield, Quality, and WUE

Interactions between irrigation and N were significant in both years for mar-ketable fruit yield, fruit quality, and water use efficiencies (Tables 2 and 3).Muskmelon yield was affected significantly by deficit irrigation treatments.Marketable fruit yield was lower in the water-stressed plants (WS and SWStreatments) compared with the unstressed (C treatment) plants. The averageyield reduction with WS and SWS treatments was 13% and 50%, respectively,compared with C treatment (Table 2). Table 3 shows that average fruit weights,fruit diameter, and fruit length were also significantly reduced by water stresstreatments (WS and SWS). Similar results were obtained by Bhella (1985) inmuskmelon and Srinivas et al. (1989) in watermelon, both of whom reportedthat water stress reduced fruit yield and quality.

Increasing N levels consistently and significantly increased yield ofmuskmelon when given adequate irrigation (C). Increasing N level from 40 to80 kg ha−1 did not affect marketable muskmelon yield statistically at p < 0.01level for the WS treatment, but increasing N from 80 to 120 kg ha−1 did sig-nificantly increase yield. It seemed that the best yield could be obtained forC and WS treatments at 120 and 80 kg ha−1 N applications, respectively. InSWS treatment, increasing N level decreased marketable yield compared with0 N application. This finding implies that increasing N level under severe watershortage causes yield reduction of muskmelon. These results are in agreement

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Table 3Mean fruit weight (FW), mean fruit diameter (FD), mean fruit length (FL) and water-soluble dry matter (SDM) of muskmelon grown with different irrigation and nitrogenlevels

2000 2001

Irr.N levels

(kg ha−1)FW(kg)

FD(cm)

FL(cm)

SDM(%)

FW(kg)

FD(cm)

FL(cm)

SDM(%)

C 0 1.0 e 19 d 11 d 7.5 d 1.1 e 20 d 10 c 7.4 d40 1.7 c 26 c 16 c 8.1 c 1.8 c 26 c 13 b 8.2 c80 2.0 b 31 b 19.5 b 8.6 c 2.0 b 32 b 16 a 8.8 c

120 2.2 a 35 a 22 a 9.0 c 2.3 a 36 a 17.5 a 9.1 cWS 0 0.7 f 15 e 8 e 8.9 c 0.7 f 16 e 8.2 cd 9 c

40 1.1 e 20 d 13 d 10 b 1.2 de 20.8 d 10 c 10.4 b80 1.5 d 24 c 17 c 10.5 b 1.7 c 25 c 13.1 b 10.9 b

120 1.5 d 19 d 12.5 d 10.8 ab 1.3 d 20 d 10 c 11.0 abSWS 0 0.6 fg 13 ef 7 e 11.6 a 0.6 fg 13 ef 7 de 11.8 a

40 0.6 fg 13 ef 6.8 e 11.5 a 0.5 gi 12.4 ef 6.7 e 11.8 a80 0.5 gh 11 ef 6.1 e 11.4 a 0.5 gi 12 f 6.5 e 11.7 a

120 0.4 h 9.5 f 5.0 e 11.5 a 0.4 i 10.5 f 5.8 e 11.7 aInteractionIrr. × N ∗∗∗ ∗∗∗ ∗∗∗ ∗∗ ∗∗∗ ∗∗∗ ∗∗ ∗∗

Note: Within each complete column, means followed by the same letter indicate nosignificant difference between treatments by two-way ANOVA at P < 0.01. Two-wayANOVA showing significant interactions of irrigation and nitrogen at ∗ = P < 0.05,∗∗ = P < 0.01 and ∗∗∗ = P < 0.001 levels.C: Well-watered, WS: water stressed, SWS: severely water stressed.

with the findings of Splittstoesser et al. (1995), who stated that moderate N ratesincrease fruit set and yield, while excessive rates of N result in decreased yield.

The predicted N rates required to attain maximum yield for muskmelonunder each irrigation treatment were calculated from regression equations(Table 4). The R2 values for these equations were highly significant (p <

0.01). Nitrogen rates required to reach maximum yields decreased as irrigationdeficits increased.

Both drip irrigation treatments and N levels affected fruit quality atP < 0.01 (Table 3). Fruit sizes and weights were highest in the control treat-ment, where they were significantly improved by increased N application rates.These parameters were reduced by water stress (WS treatment), but the 40 and80 kg ha−1 N rates significantly improved the parameters under this treatment.The lowest values for fruit weight and size occurred under severe stress (SWStreatment), and here there was no effect of N at the lowest application rate and

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Effects of Irrigation and Nitrogen Rates on Growth 631

Table 4Quadratic model regression equations for muskmelon yield response(y, t ha−1) to fertilizer N (x, kg ha−1)

Growing Irrigationseason regime Equation R2

2000 C y = 28.725 + 0.1069 x − 0.0004 x2 0.99WS y = 25.29 + 0.1347 x − 0.0008 x2 0.95SWS y = 18.51 + 0.0035 x − 0.0003 x2 0.99

2001 C y = 29.12 + 0.1305 x − 0.0006 x2 0.99WS y = 25.72 + 0.118 x − 0.0006 x2 0.95SWS y = 18.35 + 0.0138 x − 0.0004 x2 0.99

C = Well-watered; WS = water stressed; SWS = severly water stressed.

a negative effect at the two higher rates. This finding indicated that the verymarked deleterious effect of severe water stress on fruit quality was furthernegated by moderate to high nitrogen fertilizer applications.

The SDM was significantly increased by water stress (Table 3); in all caseslowest values were found in the control, and there was a significant increase inthe WS treatment and a further increase under severe water stress (SWS). Thesedata are in broad agreement with the findings of a number of other researcherswho reported a positive effect of water deficit on SDM. For example, Kirnaket al. (2001) found that water stress enhanced SDM in strawberry. Pew andGardner (1983) showed that well-watered irrigation regimes decreased SDM.Nitrogen application generally had little or no effect on SDM values; the onlysignificant exception was in the WS treatment with no applied N, where theSDM is similar to most control values.

Except for the lowest N rate, the highest IWUE values (Table 2) were inthe WS treatment. In contrast, the lowest IWUE was under SWS treatment witha N level of 120 kg ha−1. In the control, IWUE was improved by increasingN levels up to 80 kg ha−1. Under severe water stress, there was a significantlowering of IWUE at the two highest N levels. These findings are in only partialagreement with Pandey et al. (2000), who showed that IWUE increased linearlywith increasing N under a range of irrigation regimes in maize. Increases inIWUE are likely to be due to reduced water application/use, increased yield, orof both. In watermelon, Srinivas et al. (1989) reported that increases in IWUEwere due mainly to reduced water application. Our finding of highest IWUEunder moderate water stress, provided that the N level is 40 kg ha−1 or higher,might have positive implications for muskmelon culture in semi-arid situationswhere water is at a premium.

Pandey et al. (2000) stated that since water use efficiency could be improvedby either increasing yield or decreasing water use and applied irrigation water,these factors might be used by growers to decrease water use of crops while

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maintaining yield and quality. However, our data showed that yield and qual-ity were not maintained under deficit irrigation. The IWUE for drip-irrigatedmuskmelon ranged from 0.19 to 0.29 t ha−1 cm−1. In general, TWUE valuesdecreased with increasing water use. The IWUE values were higher than theTWUE values. The TWUE for drip-irrigated muskmelon were between 0.15and 0.25 t ha−1 cm−1. Since there was no rainfall during the growing season,the differences between IWUE and TWUE values can be attributed to waterused from soil storage.

Plant Growth

The effects of different levels of irrigation and N on biometric parameters (leafarea and dry-matter production) were analyzed and compared statistically withthe C treatment (Tables 5 and 6). Increasing irrigation deficit reduced the veg-etative growth parameters, with deficits WS and SWS significantly worse than

Table 5Total leaf area (LA) and leaf relative water content (LRWC) of muskmelon grownwith different irrigation and nitrogen levels

2000 2001

Irri.N levels(kg ha-1)

LA(cm2)

LRWC(%)

LA(cm2)

LRWC(%)

C 0 1515 c 88 a 1520 d 89 a40 1850 b 89 a 1856 bc 90 a80 2010 b 91 a 2019 b 90 a

120 2350 a 94 a 2400 a 93 aWS 0 1204 d 77 b 1210 e 80 b

40 1590 c 78 b 1595 d 82 b80 1700 bc 81 b 1705 cd 84 b

120 1851 b 80 b 1895 bc 83 bSWS 0 745 e 49 c 780 f 50 c

40 755 e 51 c 785 f 50 c80 725 e 48 c 745 f 48 c

120 705 e 47 c 710 f 47 cInteractionIrr. × N ∗∗ ∗∗ ∗∗ ∗∗∗

Note: Within each complete column, means followed by the same letter indicateno significant difference between treatments by two-way ANOVA at P < 0.01.Two-way ANOVA showing significant interactions of irrigation and nitrogen at∗ = P < 0.05, ∗∗ = P < 0.01 and ∗∗∗ = P < 0.001 levels.

C: Well-watered, WS: water stressed, SWS: severely water stressed.

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Effects of Irrigation and Nitrogen Rates on Growth 633

Table 6Dry weights (after fruit harvest) of muskmelon grown in different irrigation and nitrogenlevels

2000 2001

Irrigationlevel

N levels(kg ha−1)

Shoot(g/p)

Root(g/p)

Wholeplant (g/p)

Shoot(g/p)

Root(g/p)

Wholeplant (g/p)

C 0 85.4 e 7.5 d 92.9 d 88.5 d 7.9 d 96.4 e40 115.6 c 12.2 b 127.8 c 118.9 c 12.9 b 131.8 c80 142.9 b 15.4 a 158.3 b 145.2 b 16.1 a 161.3 b

120 157.4 a 16.5 a 173.9 a 159.8 a 17.4 a 177.2 aWS 0 55.1 f 5.9 e 61 e 56.1 e 6.5 e 626 f

40 85.8 e 8.1 d 93.9 d 88.1 d 7.2 de 95.3 e80 100.5 de 10.4 c 110.9 d 105.1 c 10.9 c 116 d

120 110.9 c 12.2 b 123.1 c 115.2 c 11.9 bc 127.1 cdSWS 0 38.5 g 5.0 e 43.5 f 40.1 f 4.3 f 44.4 g

40 38.4 g 5.1 e 43.5 f 40.4 f 4.2 f 44.6 g80 37.1 g 4.9 e 42 f 39.5 f 4 f 43.5 g

120 36.9 g 4.8 e 41.7 f 37 f 3.8 f 40.8 gInteractionIrr. × N ∗∗∗ ∗ ∗∗∗ ∗∗∗ ∗ ∗∗∗

Note: Within each complete column, means followed by the same letter indicate nosignificant difference between treatments by two-way ANOVA at P < 0.01. Two-wayANOVA showing significant interactions of irrigation and nitrogen at ∗ = P < 0.05,∗∗ = P < 0.01 and ∗∗∗ = P < 0.001 levels.

C: Well-watered, WS: water stressed, SWS: severely water stressed.

the control treatment. Total leaf area was reduced by deficit irrigation treatments(WS and SWS) significantly at P < 0.01 level compared with the control treat-ment (Table 5). Maximum leaf production was found at higher N rates underC treatment, as would be expected. However, water stress partially reduced thepositive effect of increasing N rates on leaf production at WS treatment. Lowleaf production under stress treatments may be due to leaf wilting. Total leafproduction under C was 2.5 times production under SWS treatment. There wasno significant difference between 2000 and 2001 in terms of leaf production.Increasing N rates at SWS did not statistically affect leaf production. A similarassociation linking growth of maize to water and N application rates has beenreported by Pandey et al. (2000). In this experiment, water stress reduced Nuptake to the plants.

Interactions between irrigation and N level were significant for plant dryweight in both years (Table 6). Increasing N applications resulted in significant(at P < 0.05) increases in biomass production of plants grown under well-watered conditions (C) and the values obtained from C + 40 kg ha−1 N treatment

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634 H. Kirnak et al.

were almost the same as those for the WS + 120 kg ha−1 treatment. Severedeficit irrigation (SWS) adversely affected total biomass yield at all N levels.Nitrogen and water stress affected shoot and root development at P < 0.05level. Both root and shoot growth were significantly affected by irrigation andN treatments (Table 6). Highest values for both parameters were in the control(C) and lowest in the SWS treatment. Increasing N improved both root and shootdry weights in C and WS treatments but had no significant effect under severewater stress (SWS). The effect of water stress on shoot growth was more obviousthan on root growth for all treatments. The highest biomass production (173.9 gper plant) was obtained at 120 kg ha−1 N level with the well-watered treatment(C). As N level increased, plant biomass production was increased except inthe SWS treatment; this effect was less marked in WS treatment compared withC treatment. These results are in agreement with the study of Edelstein andNerson (2001) on muskmelon production. Mills and Jones (1979) found that inflowering and fruiting plants, N stimulates vegetative growth, while excessiveamounts inhibit fruit development. Fernandez et al. (1996) reported that a deficitin N fertilization might cause both a delay in temporal development of the cropand a reduction in growth, biomass production, and yield.

In this experiment, root growth was less inhibited than shoot growth underboth WS and SWS treatments. This was in agreement with Sharp and Davis(1979) and Jupp and Newman (1989). Sharp (1986) showed that some rootscontinue to elongate at low soil water potential and that completely inhibits shootgrowth. Other reports (Sharp et al., 1988; Spollen et al., 1993) showed that theprimary root in several crop species could maintain significant elongation ratesat low water potential, whereas shoot elongation was much more sensitive towater stress than was root elongation.

Leaf Relative Water Content

In order to show the physiological effect of water stress, LRWC was measuredin the experiment. The LRWC was significantly reduced by water stress, withgreater reductions in the SWS treatments compared with the SW treatments. Inboth the control and water stress treatments there was no effect of increasing Non LRWC (Table 5). The declines in LRWC with WS and SWS treatments wereexpected, because soil matric potential was lower in water at stressed treatmentscompared with the control treatment (C). This result is in agreement with thefindings of Hedge (1987) in radish, Srinivas et al. (1989) in watermelon, andFernandez et al. (1996) in maize.

Leaf Nutrient Concentrations

The sufficient ranges for N, P, and K were 4.09%–5.0%, 0.25%–0.60%, and3.59%–4.50%, respectively (Jones et al., 1991). The results of this study showed

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Effects of Irrigation and Nitrogen Rates on Growth 635

Table 7Concentrations of macro elements in the leaves of muskmelon grown with dif-ferent irrigation and nitrogen levels

2000 2001

Irri.N levels

(kg ha−1)N

(%)P

(%)K

(%)N

(%)P

(%)K

(%)

C 0 4.75 d2 0.40 b 2.55 d 4.85 d 0.40 b 2.68 d40 5.16 c 0.59 a 3.80 c 5.26 c 0.60 a 3.75 c80 6.24 b 0.62 a 4.10 b 6.46 b 0.62 a 4.01 b

120 7.65 a 0.61 a 4.50 a 7.85 a 0.61 a 4.35 aWS 0 2.85 g 0.16 c 1.90 g 2.81 g 0.16 c 1.90 g

40 3.20 f 0.38 b 2.15 f 3.34 f 0.40 b 2.20 f80 3.95 e 0.40 b 2.55 d 4.05 e 0.42 b 2.45 d

120 4.52 d 0.41 b 2.80 e 4.66 d 0.45 b 2.75 eSWS 0 1.90 h 0.15 c 1.60 h 2.15 h 0.22 c 1.55 h

40 2.01 h 0.20 c 1.85 g 2.19 h 0.21 c 1.80 g80 1.95 h 0.19 c 1.90 g 2.17 h 0.22 c 1.84 g

120 1.95 h 0.19 c 1.90 g 2.22 h 0.24 c 1.85 gInteractionIrr. × N ∗∗∗ ∗∗∗ ns ∗∗∗ ∗∗∗ ns

Note: Within each complete column, means followed by the same letter in-dicate no significant difference between treatments by two-way ANOVA atP < 0.01. Two-way ANOVA showing significant interactions of irrigation andnitrogen at ∗ = P < 0.05, ∗∗ = P < 0.01 and ∗∗∗ = P < 0.001 levels.

C: Well-watered, WS: water stressed, SWS: severely water stressed, ns: notsignificant.

that most of the values for the C treatments and some of the values for the WStreatments were within these ranges, while those for the SWS treatments wereout of these ranges. Interactions of irrigation × nitrogen were significant for Nand P but not for K in both years (Table 7).

Both SWS and WS treatments significantly reduced leaf nitrogen nutri-ent concentrations compared with C (Table 7), with the lowest levels in SWS.Increasing N levels in C and WS treatments linearly enhanced leaf N concen-trations, but under severe water stress there was no effect. These results are inagreement with the study conducted with bell pepper by Simonne et al. (1998)and in maize by Pandey et al. (2000). Leaf P concentrations were highest in thecontrol and significantly lower in both water-stress treatments, with the lowestvalues occurring under severe water stress. There was little or no effect of ap-plied N concentration on leaf P in any of the treatments. This finding is in partialagreement with previous work on bell pepper (Simonne et al., 1998). Leaf Kconcentrations were also highest in the control and lower in the water-stresstreatments, with lowest values again occurring at the highest stress levels. In

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contrast to the leaf P data, increases in applied N significantly enhanced leaf Kin both the control and WS treatments but had little or no effect under severewater stress. This is in agreement with Olsen et al. (1993) working with bellpepper; these researchers showed that high N in combination with intermediateirrigation resulted in higher foliar K compared with high N in combination withlow irrigation rates.

CONCLUSIONS

Optimization of both applied N concentrations and amount of irrigation is oneof the most important agricultural management approaches in balancing cropyield and water-use efficiency in arid and semi-arid regions. Our results withmuskmelon showed that it is possible to have moderate (WS) deficit irrigationcombined with a suitable N rate and achieve high water-use efficiencies butnot maximize economic yield. The highest yield and optimum quality wereobtained from the highest irrigation and N rates. Moderate water stress (WS)reduced marketable fruit yield by about 14%–17% at moderate to high N levels.Severe water stress (SWS) had a much more marked effect, reducing marketablefruit yield by 55%–59%.

ACKNOWLEDGMENTS

This work was partially supported by the Goktepe Ltd. Co., University of Harran(Turkey) and University of Hertfordshire (UK).

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