沙漠研究 24-1, 133-136 (2014)
Ἃ₍◊✲ 24-1, 133 - 136 (2014)
Journal of Arid Land Studies
Journal of Arid Land Studies－ DT11 Refereed Paper －㸫DT11 Refereed Paper㸫

Irrigation Strategies for Vegetable Crops in Water-Limited Environments
Daniel I. LESKOVAR*1), Chenping XU1), Shinsuke AGEHARA1), Sat Pal SHARMA1) and Kevin CROSBY2)
Abstract: Water used in agriculture is considered a valuable commodity in southern regions of the U.S., such as the Wintergarden ofsouthwest Texas. This region, which is heavily dependent on underground water resources, is being seriously affected by frequentand more severe droughts, limited water resources, and increased regulations restricting water use. Several integrated strategies canbe used to increase water savings without reducing marketable yields and product quality. Those include, selecting high-efficiency
irrigation systems, applying specific growth-stage crop coefficients and evapotranspiration climatic data for irrigation management,
stressing crops to a certain profitable level, selecting cultivars with drought tolerance and growing crops when evapotranspiration
demands are low. During the last 8 years, the vegetable physiology program at Texas A&M AgriLife Research at Uvalde has been
investigating deficit irrigation (based on % crop evapotranspiration, ETc) in conjunction with specific crop strategies and irrigation
management on root and shoot growth, physiological responses, yield, quality components and phytochemical concentrations ofhigh-value specialty crops. Regulated deficit irrigation strategies (75% ETc) showed significant water savings with moderate
reductions in marketable yields and minimal to no effects in product quality and phytochemical concentrations on short-day onion(Allium cepa L.), globe artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori] and melons (Cucumis melo L.).
Key Words: Deficit irrigation, Drought, Evapotranspiration, Irrigation rates, Subsurface drip, Water use efficiency

1. Introduction
In Texas, fresh market and processed vegetables are grownon 73,700 acres with a value of $361 million (NASS, USDA,2011) and an economic impact in excess of $450 million.
The Wintergarden, a semiarid region of southwest Texas, isknown for its irrigated agriculture, particularly vegetable crops.
The region is located 110 km west of San Antonio and 140 km
from the eastern boundary of the Chihuahuan Desert. Hot
summers with moderate cool winters and annual rainfall not
exceeding 600 mm are typical. Despite the intensive irrigatedagriculture, rural communities in these regions are seriously
affected by frequent and more severe droughts, limited water
resources, and increased regulations restricting water use.
Therefore, there is an urgent need for maximizing crop water
use efficiency (WUE). In addition, the consumer demand forhigh-quality, attractive, and nutritious vegetables is rapidlyincreasing.
In the last few decades, vegetable crop WUE has been
improving with the use of efficient irrigation practices such as
drip irrigation, plasticulture, and optimum plant density.
These system components are now widely used for freshmarket vegetable production in open fields worldwide(Caliskan et al., 2009; Hanson et al., 1997; Lamont, 2005).
The improvement in WUE has been linked to reductions inrunoff and evapotranspirational losses (Jones, 2004). Deficit* Corresponding Author: d-leskovar@tamu.edu
1) Texas A&M AgriLife Research, Uvalde, TX, USA

irrigation strategies applied through drip systems have beenshown to optimize water savings and productivity in several
vegetable crops. This practice implies that water is supplied
to the crop at levels below crop evapotranspiration (ETc)deliberately, allowing crops to sustain some degree of water
deficit without significant yield reduction but with importantsavings in irrigation water.
In this paper we highlight the impact of deficit irrigation
strategies on growth, physiology, yield, quality andphytochemicals of onion, globe artichoke, and melons.

2. Materials and Methods
Deficit irrigation experiments were established on onion,
artichoke and melons at the Texas A&M AgriLife ResearchCenter, Uvalde, TX (Long. 29º1’N, Lat. 99º5’W, elevation 283m). The soil was silty clay with the following pre-plantcharacteristics: pH 7.8 to 8.0, EC 0.40 dS m-1, organic matter
2.3 to 2.6%. WUE was calculated as marketable yield
divided by total water input (t ha-1 mm-1). All data analyses
were run in SAS (version 9.2; SAS Institute, Cary, NC, USA)
or SPSS (version 14.0; SPSS, Chicago, IL, USA).
2.1. Deficit irrigation in short-day onion
Onion seeds cultivar (cv) TG 1015 were direct seeded inthe field on November 11, 2007 and October 30, 2008 at twoplanting densities (PD), 397 (standard PD) and 494 (high PD)
㸦Received, September 23rd, 2013; Accepted, February 12th, 2014㸧

2) Department of of Horticultural Sciences, Texas A&M University, College Station, TX, USA

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×1000 seeds ha-1. Three irrigation rates, 100, 75 and 50%
ETc, were imposed after plants were fully established. The
irrigation scheduling was based on the daily crop ETc of thewell-watered crop, which was calculated as the product of thedaily reference evapotranspiration (ETo) and the related onion
crop coefficient (Kc) as described in Piccinni et al. (2009).
Irrigation water was supplied using a drip tape installed at 15cm depth in the center of each bed. Harvests were done whenmore than 80% of the leaves bent over on 27 May 2008 and 18
May 2009. Bulb number, marketable yield (t ha-1) andaverage bulb size (g bulb-1) were determined. Soluble solids
content was measured with a refractometer, and pungency(pyruvic acid) and quercetin content with an HPLC. A totalof 10 onion bulbs per replication were used.
2.2. Deficit irrigation in globe artichokeTwo-month-old artichoke seedlings cv. Imperial Star weretransplanted in the field on 16 December, 2005 at 6465 plants
ha-1 and on 24 October, 2007 at 5390 plants ha-1. Threeirrigation rates, 100, 75 and 50% ETc, were imposed using thecriteria described above for onion, except that Kc was based on
the recommendation by the Food and Agriculture Organizationof the United Nations. Net CO2 assimilation rate (A) andstomatal conductance (gs) were measured during the vegetative
growth with a portable infrared gas analyzer (LI-6400;
LI-COR, Lincoln, NE, USA). Immature flower buds wereharvested eight times during 13 April and 25 May, 2006 and 12times during 20 March and 28 April, 2008. Total phenolics
content was measured using the Folin-Ciocalteu assay(Singleton and Rossi, 1965) in the edible portion of the buds
harvested in 2006.
2.3. Deficit irrigation in melon
Two irrigation rates, 100 and 50% ETc, and three melon
cultivars, Mission (cantaloupe), Da Vinci (Tuscan type) andSuper Nectar (honeydew), were arranged in a split plot
experimental design with three replications. Irrigation rates
were assigned to the main plots and cultivars to the sub plots.
Melon seeds were directly planted on raised beds (2.03 m rowto row, 0.30 m plant to plant spacing) covered with black
plastic mulch on 15 April, 2012. The irrigation was appliedwith a subsurface drip system based on the daily ETc which
was calculated as a product of ETo obtained from the lysimeter
facility located at the Texas A&M Center and the stage specific
Kc. Kc values were used as; Kc ini = 0.5, Kc mid = 0.85 andKc end = 0.60 (Allen et al., 1998). The water requirement
was calculated with adjustments for effective rainfall
availability (50%) by plastic mulch and reduced evaporation(bare soil Kc = 0.2) (Shinohara et al., 2011), effective irrigation
wetting bed width (estimated at 70%), and canopy growth.

Differential irrigation started after seedlings were fully
established. The total rainfall plus irrigation applied for eachirrigation rate was 382 and 564 mm for the 50% and 100% ETc,
respectively.
Marketable fruits were harvested at half to full slip stage.
In each harvest, fruits were counted and graded according tothe U.S. commercial trade standards (9-, 12-, 15-, 18-count per
18 kg carton). Treatments and procedures are described indetails in (Sharma et al., 2014).

3. Results and Discussion
3.1. Onion
Planting density can increase yield without additional water
input, thereby improving WUE (Shock et al., 2004; Dellaceccaand Lovato, 2000). In this study, increasing planting density
by 22% from the local commercial standard increased
marketable yield by up to 14% (Fig. 1). The limited yield
increase relative to planting density was due to 12%-13%
reductions in the average bulb size (data not shown), which is adrawback for local growers who receive higher prices forlarger bulb sizes.
Another strategy to improve WUE is to implement deficit
irrigation. Marketable yield was reduced by 8%-13% at 75%
ETc and by 19%-28% at 50% ETc compared with 100% ETc(Fig. 1). However, deficit irrigation had no effect on WUE,
while saving up to 181 mm of irrigation water (data notshown). The yield loss was due mainly to reductions in bulb
size (data not shown), suggesting that extreme deficit irrigation(50% ETc) can decrease profitability by reducing both yieldand price premiums.
It is well documented that genetics (Kalra et al., 1995) andenvironmental (soil type, climate) conditions play a major rolein determining quality and phytochemicals in onion. In thisstudy, neither deficit irrigation rates nor planting density
affected bulb quality and nutritional components in bothseasons (Fig. 2), suggesting that crop management strategies
have negligible effects on these parameters.

Fig. 1. Marketable yield of onion as affected by planting density andirrigation rate. Means with the same letter are not significantlydifferent (P < 0.05) by the Tukey test.

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Fig. 2. Nutritional quality components (means ± SE) of onion asaffected by planting density and irrigation rate: (A) soluble
solids content (SSC), (B) pyruvic acid and (C) quercetin.

3.2. Artichoke
Globe artichoke commercial production in the U.S. isalmost exclusively (> 98%) in California. In 2004-2006, theaverage marketable yield was 11.7-13.6 t ha-1 with the grossvalue of $9,983-12,340 ha-1 (Smith et al., 2008). In this study,
marketable yield at 100, 75 and 50% ETc irrigation was
13.2-17.0, 11.6-15.7 and 8.5-11.7 t ha-1, respectively (Fig. 3A),
suggesting that, even with 75% ETc irrigation, competitively
high production of artichoke is feasible in our semi-aridclimate. More importantly, in the 2007-2008 season, thismoderate deficit irrigation caused only 7% yield loss, while
increasing WUE by 15% (Fig. 3B) with water savings of 69mm (data not shown) compared with 100% ETc irrigation.
Water stress-induced stomatal closure restricts entry of CO2
and consequently limits A (Lawlor, 2002). This stomatallimitation to photosynthesis was indicated by the reductions inboth A (Fig. 4A) and gs (Fig. 4B) under deficit irrigation,
which may have limited the vegetative growth (e.g. leaf
number and plant size, data not shown) and thus productivity.
Artichoke is known as a rich source of natural antioxidants
such as phenolics (Miccadei et al., 2008). Deficit irrigation
tended to increase total phenolics content in the late harvest(Fig. 5), although this improvement in nutritional quality was
associated with reductions in head size and overall quality.
3.3. Melon
Across cultivars, deficit irrigation (50% ETc) resulted in a
31% (54.5 t ha-1 at 50% ETc vs. 78.7 t ha-1 at 100% ETc)
reduction in marketable fruit yield (MFY). Deficit irrigation
caused 23%, 30%, 33% decrease in MFY in cvs. Mission, Da
Vinci and Super Nectar, respectively (Fig. 6).
The reduction in fruit size under deficit irrigation resulted

Fig. 3. Marketable yield (A) and water use efficiency (WUE) (B) ofartichoke in response to deficit irrigation. Means with thesame letter are not significantly different (P < 0.05) by the leastsignificant difference.

Fig. 4. Gas exchange of artichoke in response to deficit irrigation:(A) net CO2 assimilation rate (A) and (B) stomatal
conductance (gS). Measurements were made on 10 April, 2008.
Means with the same letter are not significantly different (P <0.05) by the least significant difference.

Fig. 5. Total phenolics content (means ± SE) in the edible portion ofartichoke buds in response to deficit irrigation. The buds were
sampled on 20 April (early), 3 May (mid) and 25 May, 2006 (late).

Fig. 6. Marketable fruit yield (t ha-1) (means ± SE) of melons asaffected by irrigation rates on three cultivars.

in shifts in fruit size distribution in two of the cultivars (Fig. 7).
Deficit irrigation caused 48% reduction in the class 9-count,

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Fig. 7. Fruit size distribution of melons as affected by irrigation rates
on three cultivars. Marketable fruits were U.S. commercialstandards (9-, 12-, 15-, 18- and 23-count per 18 kg carton).

but a 3- and 8-fold increase in classes 12-count and 15-countsize fruit yield respectively in Mission. Similarly, underdeficit irrigation, a 19% reduction in percentage of class-9 size
fruit yields occurred in Super Nectar (Fig. 7). Yield ofmelons to water deficit conditions varied among cultivars.
The reduction in MFY in Mission was due to a decrease in fruit
size, in Da Vinci due to a decreased in fruit number, while inthe most sensitive cv. Super Nectar it was due to a reduction inboth fruit number as well as fruit size. The differential
cultivar responses to deficit irrigation indicate the need for
cultivar specific irrigation management in melons. Less
reduction in fruit yield can be attributed to the shorter growing
season of Mission (Stewart and Musick, 1982). Variablecultivar responses to deficit irrigation have also been reportedin watermelons (Leskovar et al., 2004).
Deficit irrigation can save 45% of irrigation water (227 mmin 50% ETc as compared to 409 mm in 100% ETc) in Mission
and Da Vinci cultivars with small yield reductions. However,
due to higher yield penalties deficit irrigation may not bepractical in the cultivar Super Nectar.

4. Conclusion
Drought stress and scarce water resources are the mostsignificant limiting factors affecting agricultural production in
the Wintergarden region of Texas.
Deficit irrigation
management showed significant water savings with moderate
reductions in yields and no adverse product quality changes inthree specialty vegetable crops. Our future efforts willconcentrate on identifying and integrating selective genetic
traits with irrigation management aimed to reduce the gap
between potential yield and actual yield in drought prone
environments.

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