a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1

Withholding of drip irrigation between transplantingand flowering increases the yield of field-growntomato under plastic mulch

Mathieu Ngouajio a,*, Guangyao Wang a, Ronald Goldy b

aMichigan State University, Department of Horticulture, 428 Plant and Soil Sciences Building, East Lansing, MI 48824, United StatesbMichigan State University, Southwest Michigan Research and Extension Center, 1791 Hillandale Road,

Benton Harbor, MI 49022, United States

a r t i c l e i n f o

Article history:

Accepted 30 July 2006

Published on line 11 September 2006

Keywords:

Withholding drip irrigation

Irrigation water use efficiency

Tomato

Plasticulture

a b s t r a c t

Experiments were conducted in summer of 2003 and 2004 to study the effect of withholding

irrigation on tomato growth and yield in a drip irrigated, plasticulture system. Irrigation

treatments were initiated at tomato planting (S0), after transplant establishment (S1), at first

flower (S2), at first fruit (S3), or at fruit ripening (S4). An additional treatment received only

enough water to apply fertigation (FT). Withholding drip irrigation for a short period (S2–S3)

increased tomato marketable yield by 8–15%, fruit number by 12–14% while reducing

amount of irrigation water by 20% compared to the S0 treatment. Withholding drip irrigation

also increased irrigation water use efficiency (IWUE). Similar trends were observed in 2003

and 2004 despite large differences in rainfall, heat units, and tomato yield between years.

This suggests that if soil moisture is adequate at transplanting, subsequent withholding of

irrigation for 1–2 weeks after tomato transplanting may increase yield while reducing the

amount of irrigation water.

# 2006 Elsevier B.V. All rights reserved.

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1. Introduction

Tomato (Lycopersicon esculentum) is the largest vegetable crop in

the world in terms of acreage (Ho, 1996). Tomatoes require a

high water potential for optimal vegetative and reproductive

development (Waister and Hudson, 1970). In the United States,

over 91% of tomato fields are irrigated (USDA Economic

Research Service, 2003). In Michigan, 840 ha of fresh market

tomatoes were harvested in 2004 and contributed over US$

26 million to the state’s economy (MDA, 2005a). Most produc-

tion is located in southwest Michigan where tomatoes are

producedusing drip irrigation on raisedbeds covered with black

plastic mulch. Even though in most years total precipitation

meets the water requirements for tomato production in

Michigan, rainfall varies from year to year and its distribution

* Corresponding author. Tel.: +1 517 355 5191; fax: +1 517 432 2242.E-mail address: ngouajio@msu.edu (M. Ngouajio).

0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reservedoi:10.1016/j.agwat.2006.07.007

is not uniform throughout the growing season. Therefore,

irrigation is required for profitable production. However,

optimizing water use is an economic and environmental

concern for agricultural producers. Recent adoption of the

irrigation water use generally accepted agricultural and

management practices (GAAMPs) will influence growers to

reduce irrigation input in agriculture (MDA, 2005b). Therefore,

fresh market tomato growers are interested in developing

management strategies that could help reduce total amount of

irrigation water without affecting crop yield and fruit quality.

Effects of different irrigation intervals, amounts, and

techniques on tomato yield and fruit quality have been

extensively studied (Dalvi et al., 1999; Harmanto et al., 2005;

Kirda et al., 2004; Zegbe-Dominguez et al., 2003). However,

identification of the critical irrigation stage and scheduling of

d.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1286

irrigation based on crop water status are the most cost

efficient way to improve water use efficiency (Simsek et al.,

2005). Despite the wide use of plastic mulches for fresh market

tomato production, most studies on irrigation have been

conducted on bare soil production systems (Kirda et al., 2004;

Zegbe-Dominguez et al., 2003). Results from those studies may

not apply to plasticulture systems (mainly raised beds covered

with black plastic mulch) because the mulch serves as a

barrier for water evaporation. Therefore, this study was

conducted to determine the effects of delaying the onset of

drip irrigation on fresh market tomato growth and yield in a

plasticulture system under Michigan growing conditions.

2. Materials and methods

The experiments were conducted at the Southwest Michigan

Research and Extension Center (SWMREC) at Benton Harbor

(42.1N, 86.4W; 220 m above sea level) in the summers of 2003

and 2004 on a Spinks loamy fine sand with pH of 6.5, less than

2% organic matter, and an available water holding capacity

(AWC) of about 1 mm/cm. Rainfall during the growing season

is presented in Fig. 1.

The experiment had a randomized complete block design

with six treatments and four replications. The treatments

consisted of starting irrigation at transplanting (S0), after

transplant establishment (S1), at first flower (S2), at first fruit

(S3), and at fruit ripening (S4). Another treatment received only

enough water to apply fertigation (FT). Randomization of

irrigation treatments was achieved by cutting the drip tapes

and reconnecting treatments in consecutive blocks with solid

tapes (without emitters). Individual plots consisted of one

9.1 m long bed with one row of tomato. Bed spacing was 1.7 m

(center to center) and plant spacing within the row was 46 cm.

Flow meters were connected to each irrigation line (treatment)

to record the amount of water delivered at each irrigation

event. Natural rainfall was recorded at the experimental site

using a Campbell Scientific weather station Model 012

(Campbell Scientific Inc., North Logan, UT, USA).

‘Mountain Spring’ tomato was transplanted on raised beds

covered with black plastic mulch and drip irrigated. Before

Fig. 1 – Weekly rainfall during the tomato-growing season

in 2003 and 2004.

transplanting, 224 kg/ha of 0–0–60 (N–P2O5–K2O), 168 kg/ha of

33–0–0 (N–P2O5–K2O), and 11 kg/ha of Solubor (20.5% B) were

broadcasted and disked in late April of each year. The field was

then fumigated with 392 kg/ha of methyl bromide and covered

with black plastic. Trifluralin and Sencor were applied on 14

May 2003 for weed control before tomato transplanting.

Tomato was transplanted on 24 May 2003 and 20 May 2004

when the soil was well irrigated in all treatments. During the

growing season, the insecticides (Thiodan, Asana, or Provado)

and fungicides (Bravo plus Champ or Penncozeb plus Champ)

were applied according to commercial recommendations. All

plots were fertigated weekly between mid June and first week

of September of each year with 4 kg of 4–0–8–2 (N–P2O5–K2O–

Ca). Thus, even the no irrigation treatment received some

water during fertigation.

Access tubes were installed in each treatment for weekly

monitor of soil moisture content at 30, 60, and 90 cm using a

capacitance probe (Troxler 200AP from Troxler Electronic

Laboratories Inc., Research Triangle Park, NC) connected to a

portable data logger precision irrigation scheduling method

(PRISM) from Irrigation Scheduling Methods Inc. (4147 Hamlin

Road Malaga, WA 98). Leaf water potential was measured

using the third leaflet of the third fully expanded leaf. Leaves

were collected prior to sunrise (Rudich et al., 1981), enclosed in

zip lock bags and put in a cooler. Leaf water potential was

measured after leaf collection in all treatments using a

pressure chamber (Model 600 Pressure Chamber Instrument,

PMS Instrument Company, Albany, OR, USA).

Tomato height was measured 7 August 2003 and 2 August

2004. Additionally, a trench was dug in each treatment on 23

September 2004 to measure root depth. Tomatoes were

harvested five times in 2003 (from 7 August to 18 September)

and seven times in 2004 (from 7 August to 23 September).

Tomato fruits were graded into no. 1 large (>5.4 cm), no. 1

(<5.4 cm) small, no. 2, and Cull according to standards for

fresh market grades (USDA, 1991). Fruit number and weight in

each grade category were determined.

Irrigation water use efficiency was calculated by the

following equation (Hillel and Guron, 1975):

IWUE ¼ YI � YFT

WI �WFT(1)

where IWUE is irrigation water use efficiency (kg toma-

to�1 ha �1 mm), YI is tomato yield with irrigation, YFT tomato

yield in FT (fertigation only) treatment,WI the amount of water

applied in irrigation treatments, and WFT is the amount of

water applied in FT treatment.

2.1. Statistical analysis

All data on soil water content, leaf water potential, tomato

height, root depth, and tomato yield were subjected to ANOVA

and means were separated using Fisher protected L.S.D. at 5%

level of probability. Tomato fruit number and marketable yield

were fitted to the following quadratic equation:

Y ¼ aX2 þ bXþ c (2)

whereY is fruit number or marketable yield in percentage of the

treatment with no irrigation withholding (S0), X the logarithm

a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1 287

transformation of the length of irrigation withholding in days

after transplanting (DAT) (ln(DAT)), a, b, and c are regression

parameters. The DAT at which highest values of fruit number

and yield occurred were calculated by setting the first derivative

of Eq. (1) to zero and solving for X. Then, the resulting value ofX

was put into Eq. (2) to calculate highest fruit number and yield

predicted by the regression. Eq. (2) was also set equal to 100 to

calculate the maximum length of time when irrigation can be

withheld without reduction in fruit number and yield compared

with the S0 treatment.

3. Results

3.1. Rainfall and amount of irrigation water applied

Natural rainfall varied greatly between the 2003 and 2004

seasons (Fig. 1). Total rainfall during the growing season was

162.3 mm in 2003 and 412.5 mm in 2004. In addition to greater

Fig. 2 – Soil moisture content at 30, 60, and 90 cm (percent of av

2004 under different irrigation regimes. Irrigation treatments w

establishment (S1), at first flower (S2), at first fruit (S3), or at fru

water for fertigation. Asterisks indicate significant difference be

tomato transplanting.

rainfall in 2004, there was also a more uniform rain

distribution compared to 2003. Therefore, 2003 was a dry year

and 2004 a more normal year in terms of rainfall.

Total water applied (mm) in 2003 to S0, S1, S2, S3, S4, and FT

were, respectively, 1122, 902, 773, 705, 557, and 100. The

corresponding values for 2004 were: 957, 839, 770, 728, 584, and

106. In 2004, the amount of water applied was reduced by

about 20% early in the season (treatment S0) because of more

rainfall. However, the amount of water applied in other

treatments was similar to the 2003 value.

3.2. Soil moisture during the growing season

In 2003, there were significant differences among the irrigation

treatments at all depth and throughout the growing season

(Fig. 2). Generally, the longer irrigation was withheld, the lower

the soil moisture content. The FT treatments maintained the

lowest throughout the growing season. Soil moisture declined

progressively especially at 60 and 90 cm depths.

ailable water holding capacity) in tomato field in 2003 and

ere initiated at tomato transplanting (S0), after transplant

it ripening (S4). The FT treatment received only enough

tween treatments at the specific dates. DAT is days after

a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1288

Fig. 3 – Tomato leaf water potential during growing season

in 2003 and 2004 as affected by the irrigation regime.

Irrigation treatments were initiated at tomato

transplanting (S0), after transplant establishment (S1), at

first flower (S2), at first fruit (S3), or at fruit ripening (S4).

The FT treatment received only enough water for

fertigation. Asterisks indicate significant difference

between treatments at the specific dates. DAT is days after

tomato transplanting.

In 2004, all treatments had similar soil moisture content in

the depths of 30 and 90 cm because of more frequent rainfall

(Fig. 2). However, irrigation treatments resulted in significant

differences in soil moisture content at the depth of 60 cm, with

S2 having higher soil moisture content than S4 and FT

treatments. The decline in soil moisture content observed in

2003 (dry year) was less in 2004 (wet year).

3.3. Leaf water potential

Leaf water potential was measured eight times in 2003 and

nine times in 2004 (Fig. 3). Values varied from �100 to

�1100 kPa in 2003 and from�100 to�750 kPa in 2004. Delaying

the onset of irrigation had little effect on leaf water potential in

both years. The only significant differences among treatments

were found between 82 and 96 DAT in 2003 (following a long

period of no rainfall) and at 77 DAT in 2004 (following 2 weeks

of no rainfall). Even at those dates, the only treatment that had

significantly lower leaf water potential was the FT treatment.

3.4. Tomato height and root depth

Irrigation withholding after transplanting had no significant

effect on tomato height in 2003. Tomato height was 113.7,

113.0, 110.5, 102.2, 101.6, and 96.5 cm for S0, S1, S2, S3, S4, and

FT, respectively. In 2004; however, initiating irrigation before

first flower (S2) or after fruit set (S3) produced shorter plants.

Plant height was 85.0, 86.0, 96.5, 89.0, 83.3, and 84.5 cm. Also,

delaying irrigation increased root depth in 2004. Roots were

deepest (145 cm) when irrigation was initiated at fruit ripening

in 2004 (wet year). Tomato roots were shallowest (90 cm) when

irrigation was initiated immediately after transplanting (S0).

3.5. Tomato yield

Tomato fruit number and marketable yield in all treatments

was smaller in 2004 compared to 2003 (Table 1). In 2004, the

S1 treatment had the highest tomato fruit number and

marketable yield but fruit size was similar across treatments.

In 2004; however, fruit number and marketable yield was

similar among treatments, and the S2 treatment had larger

fruits compared to S3, S4, and FT treatments. When

compared with the S0 treatment, S1 treatment in 2003 and

Table 1 – Tomato fruit number, fruit size, and marketable yielinitiation

Timing ofirrigationinitiationa

2003

Counts(�1000/ha)

Weight(tonnes/ha)

Fruit s(g/frui

S0 399.8 abb 106.5 ab 266.3

S1 449.2 a 115.4 a 257.0

S2 422.9 ab 108.3 ab 256.1

S3 402.3 b 103.2 b 256.5

S4 391.9 b 100.8 b 257.3

FT 384.1 b 86.5 c 225.9

a Irrigation treatments were initiated either at tomato transplanting (S0)

(S3), or at fruit ripening (S4). The FT treatment received only enough wab Values with same letters are not significantly different at 5% level of p

S2 treatment in 2004 increased tomato yield by 8.4 and 14.8%,

respectively, with 19.6 and 21.1% less irrigation water input,

respectively.

Tomato fruit number and marketable yield presented as

percentage of S0 was regressed against logarithm transforma-

d in 2003 and 2004 as affected by the timing of irrigation

2004

izet)

Counts(�1000/ha)

Weight(tonnes/ha)

Fruit size(g/fruit)

a 193.9 59.2 305.2 ab

a 219.1 66.3 302.5 ab

a 220.1 67.9 308.9 a

a 210.5 62.4 296.5 bc

a 210.9 61.1 289.6 cd

b 200.3 56.5 282.0 d

, after transplant establishment (S1), at first flower (S2), at first fruit

ter for fertigation.

robability.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1 289

tion of DAT. A quadratic function adequately was used to

describe the relationship (Fig. 4). The regression for fruit

number had R2 values of 0.81 and 0.97 for 2003 and 2004 data,

respectively. For marketable yield, the R2 of the regression was

0.99 in 2003 and 0.92 in 2004. The quadratic function was used

to calculate the highest fruit number and yield predicted by

the model and the DAT at which starting irrigation would

produce the highest fruit number and yield. Starting irrigation

at about 6–8 DAT would increase fruit number and yield by 9.9

and 10.6%, respectively in a dry year like 2003. Starting

irrigation at 10–13 DAT would increase fruit number and yield

by 14.1 and 15.9%, respectively in a wet year like 2004. The

Fig. 4 – Fruit number and yield of tomato in percentage of

full irrigation. Tomato fruit number and marketable yield

were fitted to Eq. (2) (Y = aX2 + bX + c) where Y is fruit

number or marketable yield in percentage of the treatment

with no irrigation withholding (S0), X the logarithm

transformation of the length of irrigation withholding in

days after transplanting DAT (ln(DAT)), a, b, and c are

regression parameters. The highest fruit number (% of S0)

was 109.9 in 2003 and 114.1 in 2004 and was achieved at

7.7 and 13.3 DAT in 2003 and 2004, respectively. The

highest yield (% of S0) was 110.6 in 2003 and 115.9 in 2004

and was achieved at 5.9 and 9.6 DAT in 2003 and 2004,

respectively.

optimal DAT to start irrigation for fruit number is later than

that for yield in both situations indicating water withholding

may result in more fruits but of smaller size.

3.6. Irrigation water use efficiency

IWUE estimates the contribution of irrigation to tomato fruit

yield. Although there was large variation in the observations, a

short delay in the onset of irrigation seemed to increase IWUE

in both years (Table 2). The highest IWUE was obtained when

irrigation was initiated after transplant establishment (S1) in

2003 and at first flower (S2) in 2004. Withholding irrigation

until the stages produced the most tomatoes per unit of

irrigation water. Beyond those stages, further delay in the

onset of irrigation reduced IWUE.

4. Discussion

The experiments were conducted in 2 years with different

rainfall amount and distribution. The 2003 season was dry and

the 2004 season wet. Variability between the two seasons was

ideal to test how rainfall can affect tomato response to drip

irrigation under plasticulture.

Measurement of soil moisture under the plastic showed that

under conditions of low rainfall (2003), irrigation treatments

have a significant effect in the entire soil profile (up to 90 cm).

However, when rainfall was adequate in 2004, soil water

content was different at thedepth of 60 cm. This is an indication

that irrigation water in the 30 cm was enough for plant growth

inall treatments and the rainfall provided sufficient water at the

depth of 90 cm. Work conducted by Machado and Oliveira (2005)

showed that most tomato roots were concentrated in the first

40 cm in the soil profile. The lack of difference in soil moisture

content at 30 cm among treatments in 2004 was probably due to

cooler conditions the uniform application of irrigation after the

treatments were initiated. Although leaf water potential

showed large differences between years, it was not a good

indicator for water status among treatments. Leaf water

potential was generally similar despite significant differences

in soil water potential. Rudich et al. (1981) showed tomato leaf

water potential was more affected by atmospheric factors than

by soil water availability. In this work, leaf water potential

decreased following long periods of drought stress and

increased after rainfall. However, differences due to the

irrigation treatments were less apparent.

Tomato fruit number and marketable yield in all treat-

ments was much smaller in 2004 compared to 2003 because of

heavy rain and cloudy weather. This suggests fresh market

tomato grown using plasticulture and drip irrigation perform

better under dry and sunny conditions (Zegbe-Dominguez

et al., 2003, 2006). Despite the large differences in rainfall and

total yield between years, the effect of withholding irrigation

on tomato growth and yield showed similar trends. This study

shows that after transplanting, it was possible to withhold

irrigation (except for weekly fertigation) for 35 days in 2003

(dry year) and 95 days in 2004 (wet year) without yield losses.

As long as there is adequate moisture in soil at transplanting,

withholding irrigation for 1–2 weeks would increase tomato

fruit number and marketable yield. However, withholding

a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 8 5 – 2 9 1290

Table 2 – Irrigation water use efficiency in 2003 and 2004 for tomato grown under different irrigation regimesa

Timing of irrigation initiationa 2003 2004

Mean Standard error Mean Standard error

S0 17.4 6.0 3.1 4.0

S1 33.4 4.1 5.3 5.8

S2 29.2 5.9 17.2 8.2

S3 24.0 3.7 9.5 8.4

S4 26.6 11.2 9.6 5.5

FT 17.4 6.0 3.1 4.0

a Irrigation treatments were initiated either at tomato transplanting (S0), after transplant establishment (S1), at first flower (S2), at first fruit

(S3), or at fruit ripening (S4). The FT treatment received only enough water for fertigation.

water further may decrease fruit number and size because of

drought stress. Such a practice requires monitoring soil

moisture status, especially during excessively dry seasons.

It has long been asserted that excessive soil moisture

during the first couple of days (or weeks) following planting

may have adverse effects on crop yield (Phene and Sanders,

1976; Sezen et al., 2006; Dalvi et al., 1999). This is clearly

supported by results in this trial. Although irrigation during

the whole growing period (S0) increased yield compared to

fertigation only treatment (FT), it had lower or equivalent yield

than withholding irrigation until the end of the transplant

establishment stage (S1) in 2003 or until first flower (S2) in

2004. Results of this study suggest growers could save up to

40% irrigation water input and improve tomato yield by up to

15% simply by withholding irrigation for a few weeks after

transplanting.

Excess irrigation not only reduces crop yield, but also

increases nutrient leaching (Moreno et al., 1996; Pang et al.,

1997; Zegbe-Dominguez et al., 2003, 2006). In most vegetable

crop fields, extensive irrigation water is applied and nitrogen

left over is much higher than cereal crops (Greenwood et al.,

1996). Withholding irrigation or reduced irrigation in the early

stage of crop growth enhanced a deeper and more extensive

root system in this study and elsewhere (Pace et al., 1999;

Ludlow and Muchow, 1990; Marouelli and Silva, 2005; De Costa

and Shanmugathasan, 1999). This would allow plants to use

water and nutrients from deeper soil, thus increase IWUE and

nutrients use efficiency, and reduce nitrogen leaching.

This study shows that delaying onset of drip irrigation after

tomato transplanting improves fresh market tomato growth

and yield while reducing the total amount of water applied

under plasticulture. These combined factors could increase

profitability of tomato production. However, the soil should be

moist at transplanting, and the exact duration of irrigation

withholding depends on natural rainfall and other environ-

mental factors. This period could range from 1 to 2 weeks or

more after transplanting. The price of tomato fruit, irrigation

cost, as well as the effect of water on fruit quality, should be

considered to maximize the profit of irrigation management.

Acknowledgements

This work was supported in part by GREEEN Project (Generat-

ing Research and Extension to meet Environmental and

Economic Needs) No GR04-008, SWMREC (Southwest Michigan

Research and Extension Center), and the Michigan Vegetable

Council. Dave Francis provided technical assistance on this

project and the summer student Adrianne helped in experi-

ment set-up and data collection. Thanks to all growers in

Southwest Michigan who contributed to the design of this

experiment by sharing their ideas and experience, and Trevor

Meachum for providing transplants in 2003.

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