water requirement of drip irrigated tomatoes grown in...

Water requirement of drip irrigated tomatoes grown

in greenhouse in tropical environment

Harmantoa, V.M. Salokhea,*, M.S. Babelb, H.J. Tantauc

aAgricultural Systems and Engineering, Asian Institute of Technology, Bangkok, ThailandbWater Engineering and Management, Asian Institute of Technology, Bangkok, Thailand

cHorticultural and Agricultural Engineering Institute, University of Hannover, Hannover, Germany

Accepted 3 September 2004

Abstract

Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop

evapotranspiration (ETc), based on Penman–Monteith (PM) method, were tested for their effect on

crop growth, crop yield, and water productivity. Tomato (Lycopersicon esculentum, Troy 489 variety)

plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system

as a control. Two modes of irrigation application namely continuous and intermittent were used. The

distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of

drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the

optimum water requirement for the Troy 489 variety of tomato is around 75% of the ETc. Based on

this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended

between 4.1 and 5.6 mm day�1 or equivalent to 0.3–0.4 l plant�1 day�1. Statistically, the effect of

depth of water application on the crop growth, yield and irrigation water productivity was significant,

while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of

ETc provided the maximum crop yields and irrigation water productivity. Based on the observed

climatic data inside the greenhouse, the calculated ETc matched the 75–80% of the ETc computed

with the climatic parameters observed in the open environment. The distribution uniformity dropped

from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental

period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was

www.elsevier.com/locate/agwat

Agricultural Water Management 71 (2005) 225–242

* Corresponding author. Tel.: +66 25245479; fax: +66 25246200.

E-mail address: [email protected] (V.M. Salokhe).

0378-3774/$ – see front matter # 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.agwat.2004.09.003

recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least

once during the entire cultivation period.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Greenhouse; Tropical region; Tomato; Water requirement; Evapotranspiration

1. Introduction

Greenhouse farming, also known as protected cultivation, is one of the farming systems

widely used to provide and maintain a controlled environment suitable for optimum crop

production leading to maximum profits. This includes creating an environment suitable for

working efficiency as well as for better crop growth (Aldrich and Bartok, 1989). The main

advantage with the greenhouse farming is that the production can be throughout the year,

which is not possible in the open field farming due to heavy rainfall and wind, especially in

tropical regions (Von Zabeltitz, 1999).

In addition, greenhouse technology can contribute to solve the global issues such as the

shortage of artificial energy, water, environmental pollution and instability of ecological

system in various ways. Creating high values for agricultural crops by using low water

inputs and high fertilizer efficiencies is one of the methods used in addressing the

environmental and resources problems. Greenhouses could be arranged with optimum

environmental medium for crop growth in order to gain maximum yield and high quality

products. Less land area is required for agriculture production system resulting in increased

land productivity (Hashimoto, 2000).

Irrigation system is one of the most important components affecting the yield and

quality of agricultural produce from greenhouse farming system. Water should be given in

proper amount and accurate time application. Therefore, water management is a key to

avoid plant moisture stress during the crop growth stages.

Several efforts have been conducted to use irrigation water as efficient as possible under

protected cultivation system. The use of drip irrigation and fertigation saves water and

fertilizer and gives better plant yield and quality (Papadopoulos, 1992). The development

of a method or model to estimate water requirement for vegetable crops is also another

great task to enhance the irrigation systems. Kirda et al. (1994) used a simple method to

estimate water use for tomato plant. The method was based on a linear relationship between

daily solar radiation and water evaporation from small beakers placed at various sites in the

greenhouse and allows for changes in plant height. The water consumptive use can also be

predicted using the maximum evapotranspiration (ETm) from its soil water potential. For

pepper, Chartzoulakis and Drosos (1997) have investigated that water amount equal to 0.85

� ETm had no effect on plant growth and fruit yield. Folegatti et al. (2001) also studied on

varying irrigation deficit based on fractions of pan evaporation. Fricke (1998), on other

hand, used the surplus irrigation method up to 40% of permanent irrigation to irrigate

tomato crops under greenhouse. The result showed that plants growth and yield were better

in higher surplus irrigation.

Lee and Shin (1998) investigated an optimal irrigation management system of

greenhouse tomato based on the bio-information of the plant. It was found that the micro

Harmanto et al. / Agricultural Water Management 71 (2005) 225–242226

variation of stem diameter reflected the water status of tomato plant and could be utilized as

a criterion for timing of irrigation.

Research on crop water requirement under greenhouse has been carried out in the

temperate region. In Netherlands, it has been reported that water consumption for tomatoes is

estimated at 0.5–0.9 m3/m2 greenhouse area per year (Papadopoulos, 1991). Another study

conducted by Soria and Cuartero (1998) revealed that plant water consumption of tomatoes

ranged from 0.19 to 1.03l plant�1 day�1 at different water salinities. In Mediterranean area,

the optimum water requirement for vegetables was still not clearly stated, but pan evaporation

method within the greenhouse was used to estimate water consumption use (Abou-Hadid et

al., 1994; Tuzel et al., 1994). Increasing the irrigation rate up to 120% of pan evaporation

increased crop yield but decreased total soluble solids (Tuzel et al., 1994). In another region,

the volume of irrigation water will vary depending on the season and the size of tomato plants

cultivated in a gutter-connected plastic greenhouse. New transplants need only about

0.05l plant�1 day�1. At maturity on sunny days, however, plants may need up to

2.7l plant�1 day�1. Generally, about 1.8l plant�1 day�1 are adequate for fully grown or

almost fully grown tomato plants (Snyder, 1992).

Compared to the temperate areas where the greenhouses are widely used and well

developed, not much information about the application of micro irrigation in greenhouses

under varying climatic conditions in the tropical environment is available. Moreover,

investigation on water requirement of vegetables under tropical greenhouse is still limited.

However, research on greenhouses in the tropics has been started in India (Tiwari, 1996)

and subtropical regions like China (Zhou et al., 2003). A study conducted in India mentioned

that water requirements of crops in protected cultivation have a diurnal and seasonal

fluctuation which is similar to the productivity variation of solar stills. Both processes are

primarily driven by the varying solar irradiation (Chaibi, 2003). For tomato crops cultivated

under Indian greenhouse, it is recommended that daily amount of required water for different

growing system varies from 0.89 to 2.31 l plant�1 day�1 (Tiwari, 2003; Tiwari et al., 2000).

They also noted that the irrigation water should be given on every alternate day.

In accordance with some research findings mentioned above, it is evident that the crop

water requirements could be different from one region to the other region. This paper

investigates the optimum irrigation requirements for tomatoes grown under a

polyethylene-net greenhouse system in a humid tropic region. The methods to estimate

water requirement and how to apply irrigation water for tomato crops are discussed. The

main goal of this research was to evaluate the water requirement for the tomatoes grown

with drip fertigated irrigation system in tropical greenhouse conditions (Harmanto, 2002).

The specific objectives of the study were to: (1) determine the optimum water requirement

of drip irrigated tomato plants; (2) compare the evapotranspiration estimated from

microclimate inside and outside the greenhouse, and (3) assess the drip system

performance under greenhouse condition.

2. Materials and methods

Field experiments were carried out at the greenhouse complex at the Asian Institute of

Technology, Bangkok, Thailand (138380N latitude and 1008220E latitude) from February to

Harmanto et al. / Agricultural Water Management 71 (2005) 225–242 227

June 2002. A greenhouse with the size of 10 m � 20 m using 40-mesh size cladding

material was used for the experiment. The greenhouse was equipped with two fans to

exhaust the hot air out from the greenhouse.

For measuring microclimate inside the greenhouse, air temperature and relative

humidity were measured by thermocouple sensors K type (NiCr–Ni) in the aspirated

Psychrometer ITG, placed 0.5 m above the plants. Incoming solar radiation was

measured by Pyranometer CM 11/14 type with sensitivity between 4 and 6 mV/W m�2

and the daily total error of 2% of measurement (Kipp and Zonen, Delft, The

Netherlands) which is placed at the center of greenhouse 2.5 m above the floor. The

handy vane anemometer was used to measure daily wind speed at 2 m above ground

level. In order to record outside climatic condition, a simple meteorological station was

installed 10 m apart from the greenhouse. The station consists of an aspirated

Psychrometer ITG to measure air dry and wet bulb temperature, a Pyranometer CM 11/

14 type sensor to measure global solar radiation, a rainfall sensor and two wind sensors,

placed 10 m above the ground level, to measure wind speed and wind direction. All data

were measured at an interval of 15 s, using a data logging system (ITG, Hanover,

Germany). Average values were stored every minute on the disk for further evaluations.

The placement of all sensors in the greenhouse and at the meteorological station is

shown in Fig. 1.

A drip irrigation network consisting of different sizes of emitters, two small pumps and

two plastic tanks of 350 l capacity each was designed to apply varying amount of water for

the treatments (Fig. 1). The irrigation treatments consisted of four levels of irrigation

amount based on crop evapotranspiration (ETc) calculated from climatic conditions outside

the greenhouse and two irrigation modes based on the number of irrigation applications per

day, defined as:

� T1—25% of ETc;

� T2—50% of ETc;

� T3—75% of ETc;

� T4—100% of ETc;

� C—continuous mode with water application at once a day;

� I—intermittent mode with water application at three times a day.

All treatments were arranged randomly with three replications for each treatment as a

block, as also shown in Fig. 1. The control treatment was an open system with 100% of ETc

of irrigation water level, and it was located just along side the greenhouse.

The amount of irrigation water to be applied for the experiment was estimated using the

crop evapotranspiration (ETc) for tomatoes which was calculated by the FAO Penman–

Monteith method (Allen et al., 1998) based on the climatic data observed outside the

greenhouse. The FAO Penman–Monteith equation is as follows:

ETc ¼ Kc0:408DðRn � GÞ þ gð900=Tmean þ 273Þu2ðes � eaÞ

Dþ gð1 þ 0:34u2Þ(1)

where ETc is crop evapotranspiration under standard condition (mm day�1), Rn net radi-

ation at the crop surface (MJ m�2 day�1), G the soil heat flux density (MJ m�2 day�1)



Fig. 1. Schematic description of experimental greenhouse with the measuring system, the irrigation network of

two pumps, fertilizing solution (tanks), three lateral lines and the layout of the treatments.

which is relatively small and ignored for day period, Tmean the mean daily air tempera-

ture at 2 m height (8C), u2 the wind speed at 2 m height (m s�1) (es � ea) the vapor

pressure deficit (kPa), D the slope of vapor pressure curve (kPa 8C�1), g the psychrometric

constant (kPa 8C�1) and Kc the crop coefficient (between 0.45 and 1.05) which is affected

by several factors such as crop type, crop height, albedo (reflectance) of the crop-soil

surface, aerodynamic properties, leaf and stomata properties and crop stages (Allen et al.,

1998).

A set of the climatic data, air temperature, relative humidity, wind speed and global

solar radiation outside the greenhouse was needed for estimation. Smith (1992) developed

the CROPWAT Software version 7.0 under DOS. It was used to calculate the crop water

requirement. In agreement with Schwab et al. (1993), it was observed that almost 85% of

the soil area was covered by mature tomato plants. The percentage of total area shaded by

the crop was assumed to vary from 50% for initial stage to 85% for full maturity stage of

crop growth. An overall irrigation efficiency of 90% was assumed for all the treatments in

the calculation of irrigation requirement.

Due to the cultivating system of tomatoes which were planted in the soil pot, irrigation

water was applied in a precise amount. Table 1 shows the amount of water applied to each

plant for different treatments in l plant�1 day�1. The tomato plants with 100% of ETc (T4)

treatment, for instance, received a total of about 44 l of irrigation water during the crop

season. Similarly, for 75% of ETc, 50% of ETc and 25% of ETc treatments the irrigation

water applied were 33, 22 and 11 l, respectively, during the entire experiment. For the

control treatment, the amount of irrigation water, which was equivalent to 100% of ETc

minus the depth of precipitation at the respective day, was applied. A total amount of 27.1 l

of water was given to the plants during the experiment.

Tomato variety, TROY 489, which is a cherry type, photo insensitive, disease resistant

and high yielding, was selected for this study. It was grown in pots with a surface area of

706.5 cm2. Seedlings were sowed 30 days before transplanting activity. Fertilizer was

given directly to the plant with the irrigation water. The fertilizer solution of NPK (25% of

N, 5% of P2O5 and 5% of K2O) with 200 ppm concentration was applied as a common

method for tomato cultivation.

The substrate soil, consisted of organic matter of 28%, pH of 5.3 and the soil texture of

30% sand, 39% silt and 31% clay, was used in this experiment. The soil was initially a good

media due to its rich organic matter content needed for the better plant growth. The soil

water holding capacity was around 0.64 cm3 cm�3. The soil volume in each pot was

8000 cm3.

Harvesting was done manually from 65 to 90 days after transplanting. The total tomato

fruits produced were weighed using a digital balance of Scaltec SBA 51 with the accuracy

of 0.01 g. The measurement of crop yield was randomly done from targeted plants. The

quality of tomatoes was also quantified by two parameters, i.e. fruit diameter and fruit

weight.

In order to evaluate the plant growth of tomato, some parameters of plant height, stem

girth, and leaf area index (LAI) were measured. The measurements were taken every 3 days

during the experimental period. LAI was measured directly by harvesting all green healthy

leaves from a prescribed area, then measuring and summing the areas of individual leaves

using photometric methods. The digital area meter Model L1 3100 was used for this


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Table 1

Water applied in different treatments

Month Decade No. of

days

Crop

stage

ETo Reff

(mm day�1)

Crop

coeff, Kc

Pvalue

(%)

ETc

(mm day�1)

The amount of irrigation applied per treatment

T1 (l plant�1) T2 (l plant�1) T3 (l plant�1) T4 (l plant�1) Control

(l plant�1)

February 2 1 Init.a 4.1 0.45 50 1.45 0.03 0.05 0.08 0.10 0.31

February 3 8 Init. 4.1 0.45 50 1.45 0.20 0.41 0.61 0.82 0.65

March 1 10 Init. 4.3 0.45 50 1.52 0.27 0.54 0.80 1.07 1.07

March 2 10 Init./dev. 4.3 0.49 60 1.98 0.35 0.70 1.05 1.40 1.40

March 3 11 Dev. 4.3 0.64 70 3.02 0.59 1.17 1.76 2.35 2.35

April 1 10 Dev. 5.3 0.85 75 5.30 0.94 1.87 2.81 3.74 2.52

April 2 10 Dev./mid 5.3 1.00 80 6.65 1.17 2.35 3.52 4.70 3.03

April 3 10 Mid 5.3 1.05 80 6.98 1.23 2.47 3.70 4.93 4.52

May 1 10 Mid 5.2 1.05 85 7.28 1.29 2.57 3.86 5.14 5.14

May 2 10 Mid 5.2 1.05 85 7.28 1.29 2.57 3.86 5.14 3.15

May 3 11 Mid/late 5.2 1.04 85 7.21 1.40 2.80 4.20 5.60 2.38

June 1 10 Late 4.6 0.99 80 5.71 1.01 2.02 3.03 4.04 0.50

June 2 10 Late 4.6 0.89 80 5.14 0.91 1.81 2.72 3.63 0.22

June 3 4 Late 4.6 0.82 80 4.73 0.33 0.67 1.00 1.34 0.03

Total 125 11.00 22.01 33.01 44.01 27.27

a Init.—initial; dev.—development; mid—middle, Pvalue is the percentage of shading by canopy.

purpose. Irrigation water productivity (IWP) was also calculated as a fresh fruit tomato

yield divided by volume of irrigation water applied.

The performance of drip irrigation system was evaluated by calculating the distribution

uniformity (DU), flow rate and pressure drop in the system. The DU was determined by

measuring the flow rate from the emitters and using the following equation (Schulbach et

al., 1999):

DU ¼ ðQeÞat 25%

Qe

�100% (2)

where DU is the distribution uniformity (%), (Qe)at 25% the average flow rate of the emitters

in the lowest quarter of all flow rate measurements (l min�1), and Qe the average flow rate

(l min�1). The DU was measured three times during the experiment, i.e. before transplant-

ing, during plant growth and after harvesting.

Analysis of variance (ANOVA) was used for analyzing the effect of the treatments (the

amount of irrigation application and irrigation mode) on IWP, leaf area index (LAI), plant

height and crop yield of tomatoes. Each treatment with three replications (as blocks) was

also analyzed. In order to emphasize any different means of the treatments, LSD-method,

one of the multiple comparison tests, was used.

3. Results and discussion

3.1. Microclimate inside and outside the greenhouse

The daily microclimate under greenhouse and open environment from weather data

during the experimental period is presented in Fig. 2. The average temperature inside and

outside the greenhouse was almost similar. This may be due to the usage of the perforated


Fig. 2. The daily microclimate conditions (air temperature and relative humidity) between inside and outside the

greenhouse during the experiment.

polyethylene (net) as a wall for the greenhouse. The hot air from inside the greenhouse

could easily be released to the atmosphere through the net. On average, the air temperature

difference between inside and outside the greenhouse was about 2–3 8C. The air

temperature inside the greenhouse was higher than the outside the greenhouse. From the

initial stage to the middle stage, the temperature difference was very close then it was

gradually increased after 50 days after transplanting from 1 to 5 8C due to the climatic

changes. On the contrary, the relative humidity inside the greenhouse humidity was about

5% lower than the outside environment. Two fans installed at the greenhouse may take the

water vapor off from inside the greenhouse. The fans were set at the temperature above

25 8C to be operated. Consequently, the fans were working everyday.

Wind speed in the greenhouse as expected, was much lower than outside. The net wall of

the greenhouse protected the crop against the wind. The advantages of low wind speed

include low evapotranspiration process, encouraged crop growth and need of less water.

The average wind speed inside the greenhouse varied from 0.6 to 0.8 km h�1, while outside

it varied from 3.5 to 19.5 km h�1 as shown in Fig. 3.

On average, the daily measured solar radiation inside the greenhouse was 187 W m�2

compared to 290 W m�2 for the open system (Fig. 3). It means that the plants inside

greenhouse received about 35% less energy from global solar radiation than the outside the

greenhouse. The type of roof material used caused the reduction of the total solar radiation

in the greenhouse. The reduction of solar energy received by the plants also results in

reduced evapotranspiration.

3.2. Water requirement under the greenhouse

The crop evapotranspiration in the greenhouse (ETc in) calculated from climatic data

from inside the greenhouse and crop evapotranspiration outside the greenhouse (ETc out)

calculated based on the observed weather data during the experiment are compared in


Fig. 3. The daily incoming solar radiation and wind speed between inside and outside the greenhouse during the

experiment.

Fig.4. The estimation is based on Penman–Monteith (PM) equation (Allen et al., 1998).

Results show that the ETc in values were lower than ETc out of the open environment.

During the initial stage of crop, the difference between the ETc in and ETc out was only

about 5%. At middle and late stages, the difference was gradually increased up to about

30%. On the average, the ETc in was about 75% of the ETc out. It is clear that crop water

requirement in the greenhouse was less than crop water requirement outside the

greenhouse.

Since the application of Penman–Monteith (PM) equation was used for estimating

tomato water requirement, the microclimate data plays an important role for irrigation

planning. With the appropriate climatic data measured in the greenhouse, crop water

requirement could be predicted using the evapotranspiration equation from PM model.

This method was also applied to the greenhouses by other researchers (Tiwari, 2000;

Chartzoulakis and Drosos, 1997; Eliades and Orphanos, 1986; Baille, 1994). Baille (1994)

claimed that the PM model is believed to be the best adapted to estimate crop water

requirements, but requires more sensors for measuring microclimatic parameters i.e. air

temperature, relative humidity, wind speed, global solar radiation, soil temperature as well

as specific crop parameter such as the aerodynamic, stomata conductance and leaf

temperature. At present, the most irrigation of greenhouse crops is mainly controlled on the

basis of solar radiation due to unavailability of sensing devices and cost consideration.

The method, which is also applied on the current research, shows a dramatic result and

appropriate tool to decide on watering tomato crops inside the humid tropic greenhouse.

The daily water requirement for tomato fluctuated and was in accordance with the

microclimate on the respective day and growing stage of the plants. This benefited to

improve the existing irrigation system. So, by applying the method of watering crops based

on most daily climatic data from inside greenhouse directly, it is quite possible that the

irrigation system can become more precise.

Fig. 4 also depicts the amount of water applied at 100% of ETc (T4 treatment) calculated

based on the microclimate of the open environment. It matched well with the ETc out. The


Fig. 4. Crop evapotranspiration inside (ETc in) and outside (ETc out) the greenhouse.

ETc in was about 25–30% lower than the actual water applied to the crop. It was evident

from the development stage of crop growth up to the harvesting stage that the ETc in

fluctuated between 5 and 6 mm day�1 while the tomato crop was given irrigation water of

about 6–7 mm day�1 similar to the ETc out.

The range of irrigation water, 5–7 mm plant�1 day�1 or 0.35–0.50 l plant�1 day�1

obtained in this research was different from those reported as 1.8 l plant�1 day�1 by Snyder

(1992); 0.19–1.03 l plant�1 day�1 by Soria and Cuartero (1998); and 0.89–

2.31 l plant�1 day�1 by Tiwari (2000). These comparisons are taken as a partial validation

of the water requirement of tomato grown in this study under humid tropics. Not only do

microclimate parameters affect the crop water requirement, but also it depends very much

upon crop variety, season and the method of tomato cultivation.

3.3. Observations about crop growth

Table 2 presents the effect of water application on crop height at 75 days of

transplanting. The plants attained higher heights for T2, T3 and T4 treatments compared

to the T1 and control treatments. The T3 treatment gave the highest plant height

compared to others, i.e. up to 1.49 m at 75 days after transplanting and it could reach up

to 2 m at the time of harvesting. Meanwhile, T1 and T4 treatments have a similar mean

value of 1.42 m height at continuous irrigation. This gives an idea that either deficit or

over irrigation was not giving the maximum plant growth for tomato. In contrast, the T1

treatment gave the lowest plant height, i.e. up to 1.10 m and it was almost similar to the

control at 0.84 m.

Statistically, the effect of irrigation mode on crop height was significant at 5% level. The

continuous irrigation mode proved to be relatively better for crop growth in terms of plant

height than the intermittent irrigation mode. This indicated that the irrigation water was

directly used by the plants for photosynthesis at the day time rather than it was given at the

afternoon (for intermittent mode). The water holding capacity of soil used was sufficient to

store the moisture when it was irrigated. Similarly, the water irrigation amount significantly

affected the crop height at 5% confidence level. The T3 treatment was the best treatment

and gave the highest plant height. Both T2 and T4 treatments gave a similar average plant


Table 2

Plant height as a function of water application treatments

Treatment Crop height (m)

Continuous irrigation mode Intermittent irrigation mode

Block 1 Block 2 Block 3 Mean Block 1 Block 2 Block 3 Mean

Control 0.78 0.89 0.86 0.84 a 0.69 0.89 0.91 0.83 a

T1 1.16 1.10 1.03 1.10 b 1.06 0.84 1.01 0.97 b

T2 1.43 1.40 1.47 1.43 c 1.35 1.27 1.47 1.36 c

T3 1.47 1.56 1.45 1.49 d 1.48 1.56 1.37 1.47 d

T4 1.49 1.35 1.41 1.42 c 1.50 1.37 1.33 1.40 c

Mean 1.27 1.26 1.24 1.26 a 1.22 1.19 1.22 1.21 b

Means with the same letter within a column is not significantly different from each other at the 0.05 level t-test

(LSD).

height. The smallest plants were observed for the T1 treatment followed by the control

treatment.

The active LAI is the index of the leaf area that actively contributes to the surface heat

and vapor transfer. The T2, T3 and T4 treatments gave higher LAI than the T1 and control

treatments for both continuous and intermittent irrigation application modes (Fig. 5). The

maximum LAI achieved with the T3 treatment was about 4.8 for the intermittent and 4.3

for continuous irrigation mode. The LAI values for T4, T2 and T1 treatments were 4.0, 3.8

and 2.0, respectively, for both irrigation modes. For the control, the maximum LAI was 1.7

for intermittent and 1.9 for continuous irrigation modes. Thus, in terms of LAI, the T3

treatment gave the best performance compared to other treatments. Allen et al. (1998)

stated that the LAI values commonly vary from 3 to 5 for mature crops and differ among

varieties.

The LAI, as shown in Fig. 5, is the peak value of LAI representing the flowering stage of

crop leading to the formation of fruits at the maturity stage. The plant leaf growth was

affected by water availability. The crop that received more than 50% of ETc out had the LAI

up to 3.5, indicating good plant growth. For the T1 treatment, on the contrary, the

maximum LAI was less than 2.0, indicating poor crop growth leading to low crop yield, as

discussed in later part of the paper.

3.4. Tomato yield and product quality

Since the crop variety of tomato used for the experiment was F1 Hybrid, Troy 489, a

cherry type tomato, the fruits produced were very small in size and weight. According to

Chiathai Seed Company of Thailand (the producer of this variety), Troy 489 has unique

characteristic which is vigorous with good disease tolerance, heat resistance, sweet-tart

flavor and can produce many clusters of round bright red fruits. The reported physical

properties of tomatoes are 25 mm � 25 mm average size, having red color and 5–10 g

weight per fruit.

Even though the fruits were small with weight ranging from 5 to 10 g per fruit, the

number of matured fruits per plant was high, especially in the T3 and T4 treatments. The


Fig. 5. Crop LAI for continuous and intermittent modes at different treatments.

number of fruits per plant was between 30 and 60 fruits depending upon the amount of

water applied to the plant.

The tomato yields for different treatments (Table 3) indicated that the T3 treatment gave

the maximum crop yield of 0.44 and 0.41 kg m�2 of tomato for the continuous and

intermittent irrigation modes, respectively. For the continuous mode treatment, the yields

for T4, T2 and T1 treatments were 0.40, 0.20 and 0.04 kg m�2 while for the intermittent

mode; the yields for T4, T2 and T1 treatments were 0.34, 0.24 and 0.06 kg m�2,

respectively. Statistically, there was no significant difference between two irrigation modes

on tomato yield at confident level of 5%. The crop yield for the control was low and close to

that of the T1 treatment. This is due to higher wind speed outside where it was nearly 10

times compared to inside the greenhouse (see Fig. 3 about microclimate condition between

inside and outside the greenhouse). The evaporation rate of the plants was higher than in

the greenhouse, so that the plants were not grown as expected. Moreover, open cultivation

could not protect the plants against diseases compared to cultivation inside the greenhouse.

As the result, the control treatment of 100% ETc out water application gave the lowest plant

height, lowest LAI and lowest tomato yield. So, the cultivation in the open system is not

recommended to maximize the tomato yield throughout the year.

An average irrigation rate of 0.5 l plant�1 day�1 was found to be optimum amount of

water for maximizing the ‘‘cherry’’ tomato yield used in this study. The application of

irrigation at lower amount (deficit irrigation) of the water requirement gave lower yield.

But increasing the irrigation water over a certain level (over irrigation) did not increase the

tomato yield above the maximum yield. So, the irrigation should be given as precise as

possible to the plant close to the optimum. The optimum amount of irrigation was very

close to the crop evapotranspiration which was calculated from the dynamic microclimate

inside the greenhouse during the experiment (Fig. 4).

As stated earlier, two parameters, i.e. fruit diameter and fruit weight were used to

evaluate the quality of tomato. In general, each of the treatment produced almost uniform

size of tomatoes with diameter varying from 20 to 25 mm except the control and T1

treatments, which had the average tomato diameter of 16–17 mm. Results suggested that

the different treatments tested in the greenhouse gave similar results about the tomato

quality. Both irrigation water amount and irrigation application mode did not affect the


Table 3

Tomato yield with different treatments

Treatment Tomato yield (kg m�2)



Control 0.09 0.07 0.08 0.08 a 0.09 0.07 0.08 0.08 a

T1 0.05 0.04 0.04 0.04 a 0.06 0.05 0.07 0.06 a

T2 0.16 0.24 0.21 0.20 b 0.13 0.25 0.33 0.24 b

T3 0.43 0.35 0.56 0.44 d 0.44 0.48 0.33 0.41 d

T4 0.41 0.36 0.31 0.36 c 0.36 0.30 0.35 0.34 c

Mean 0.23 0.21 0.24 0.22 a 0.22 0.23 0.23 0.22 a


(LSD).

fruit quality. The control that represents open farming system gave smaller size tomatoes

compared to that cultivated in the greenhouse.

3.5. Irrigation water productivity

Irrigation water productivity (IWP) represents the productivity of irrigation water

related to the crop yield. The T3 treatment was found to be the best treatment in terms of

irrigation water productivity. For the T3 treatment, mean values of irrigation water

productivity for continuous and intermittent irrigation modes were 0.95 and 0.88 kg m�3,

respectively. Table 4 shows that the T4 treatment with water productivity of 0.65 and

0.51 kg m�3 for continuous and intermittent irrigation modes showed lower performance

than the T2 treatment. It was evident that over irrigation resulted in lower water

productivity. Lack of irrigation, on the other hand, can cause very low water productivity as

proved by the control results. It can be concluded that cultivating under greenhouse could

increase productivity by 4–5-fold compared to the control.

Analysis of variance for split plot design was used to analyze the effect of irrigation

amount and irrigation mode on crop growth, crop yield and irrigation water productivity.

The irrigation amount affected the water productivity. The control treatment showed the

minimum irrigation water productivity. The highest water productivity was reached with

75% of ETc (T3) treatment. The intermittent application of irrigation provided slightly

higher water productivity than the continuous irrigation application. However, the two

irrigation application modes statistically did not show any significant difference in the

water productivity at 5% level of significance.

A similar study on the effect of different irrigation interval on spring season glasshouse

tomato production was also carried out (Tuzel et al., 1994). The irrigation interval applied

on the watering method did not significantly affect the crop yield, but affected other

parameters, i.e. total soluble solid, dry matter content, pH and skin resistance were slightly

changed during harvesting period. However, giving irrigation at the appropriate times and

consistency will probably help to protect fruit disorders such as fruit cracking, puffiness,

sunscald, catfacing or blossom end rot (Peet, 1995). When water availability fluctuated or

when it is too high or too low at critical stages, especially during the fruiting period, tomato


Table 4

Irrigation water productivity under different treatments

Treatment Irrigation water productivity (kg m�3)



Control 0.22 0.18 0.19 0.20 a 0.22 0.17 0.20 0.20 a

T1 0.33 0.25 0.23 0.27 a 0.40 0.31 0.45 0.39 a

T2 0.51 0.76 0.67 0.65 b 0.43 0.79 1.06 0.76 b

T3 0.91 0.75 1.19 0.95 c 0.93 1.02 0.70 0.88 c

T4 0.66 0.57 0.51 0.58 b 0.49 0.48 0.56 0.51 b

Mean 0.53 0.50 0.56 0.53 a 0.49 0.55 0.59 0.55 a


(LSD).

fruit disorders will easily develop. Therefore, the irrigation mode studied in this research

work was found to be the most important consideration.

3.6. Performance of drip irrigation system in greenhouse

The details of the performance of drip fertigated irrigation system during the experiment

are presented in Table 5. The overall DU of the system ranged from 90.58 to 97.58% which can

be categorized as excellent since the DU values were up to or equal to 90% (Schulbach et al.,

1999). The DU dropped by about 3–5% from the start to after 95 days of the system use. This is

due to emitter clogging caused by deposit of some minerals from fertilizer solution and some

algae. The use of disk filtration of 150 mm could only reduce a particular mineral but the algae

were still a problem in the emitter. The emitter types of 2 (with CVequal to 0.03) and 6 l h�1

provided higher distribution uniformity index than the other two types of emitters. Both after

45 and 95 days of the system use, there was no significant difference in the distribution

uniformity of the irrigation network system at the 5% confidence level.

Table 5 also shows that the flow rate of each emitter was not far from the flow rate at the

start of the experiment. The 2 l h�1 emitter, for instance, delivered 1.79 l h�1 on the

average during the experiment. There was 10% error from the actual to the desired flow

rate. Similarly, the error for other emitters was between 3 and 8%. It was observed from

Table 4 that the flow rate of emitters at the start of experiment was not the same as the rated

emitter discharge. The 2, 6 and 8 l h�1 emitters delivered lower and the 4 l h�1 emitter gave

higher discharges than the rated discharge rates.

The average DU at mid-stage (after 45 days) and at the end of the experiment (after 95

days) was 92.62 and 92.16%, respectively, a small difference between the DU after 45 and

95 days of the system use. Statistically, however, there was no significant difference in the

DU during the experiment. Similarly, both block and irrigation method treatments did not

affect the DU of irrigation network. Therefore, it can be concluded that the application of


Table 5

Performance of irrigation network during the experiment

No. Parameters Emitter typesa Average

2 l h�1 4 l h�1 6 l h�1 8 l h�1

1 Overall DUb (%)

a Start (0 days) 96.68 95.28 97.58 94.46 96.00

b Mid (after 45 days) 94.37 93.44 91.24 91.42 92.62

c End (after 95 days) 92.61 90.58 93.64 91.79 92.16

2 Overall DU drop (%) 4.2 4.9 4.0 2.8 4.0

3 Flow rate (l/h)

a Start (0 days) 1.87 4.28 5.73 7.47

b Mid (after 45 days) 1.70 4.65 6.03 7.30

c End (after 95 days) 1.81 3.99 5.64 7.19

4 Flow rate drop (%) 2.9 6.7 1.6 3.8 3.8

5 Deviation in flow rate (%) 10 8 3 8 7.5

a DU = distribution uniformity of emitter.b Operating with 30 m pressure head and 40 l/min discharge of water pump.

200 ppm of fertilizer in irrigation water did not significantly affect the performance of drip

irrigation system during the experiment.

The emitter characteristics provided by manufacturer indicated that the constant flow

rate from the emitter can be achieved at pressure range of 98–294 kPa. The pressure head

on the emitters in the system was within the range recommended by the manufacturer.

Therefore, it can be said that the pressure drop along the laterals had no effect on the emitter

discharge during the experiment.

4. Conclusions

For growing tomatoes, greenhouse farming system performed better than the open

farming system in terms of crop yield, irrigation water productivity and fruit quality. The

results revealed that the crop evapotranspiration inside the greenhouse matched the 75–

80% of the crop evapotranspiration computed with the climatic parameters observed in the

open environment. In other words, the greenhouse farming with drip irrigation can save

about 20–25% of water compared to the open drip irrigated farming system.

The amount of water applied significantly affected the crop growth, crop yield and

irrigation water productivity. No significant effect of the irrigation mode namely either

continuous or intermittent irrigation mode on crop yield or quality was observed. The

optimum water requirement for Troy 489 variety of tomatoes grown in the greenhouse was

around 75% of the crop evapotranspiration (ETc) calculated based on the climatic data

observed in the open system. The actual irrigation water for tomato crop in tropical

greenhouse environment was found to vary from 4.1 to 5.6 mm day�1, which is equivalent

to 0.3–0.4 l plant�1 day�1.

Drip irrigation applied with 75% of crop evapotranspiration (ETc) was found to be the

optimum irrigation amount for humid tropic environment in order to obtain the maximum

tomato yield of 0.44 kg m�2 and water productivity of 0.92 kg m�3.

The use of PM method at optimum level of 75% of ETc for estimating crop water

requirement under greenhouse based on daily microclimate outside or beyond greenhouse

environment where air temperature, relative humidity and wind speed are not very different

between inside and outside the greenhouse is still acceptable. For the other climates where

these differences are very large this method could not probably be applied. It is

recommended that the estimation of crop water requirement from evapotranspiration

equation by measuring microclimates directly from inside the greenhouse might be the

more appropriate way.

Acknowledgements

The authors are grateful to the donors of Protected Cultivation Project, namely German

Research Foundation (DFG), Ministry for Economic Cooperation and Development

(BMZ), Germany, and University of Hannover in collaboration with Asian Institute of

Technology, Thailand for providing financial support and facilities to carry out this

research work.


References

Abou-Hadid, A.F., El-Shinawy, M.Z., El-Oksh, I., Gomaa, H., El-Beltagy, A.S., 1994. Studies on water

consumption of sweet pepper plant under plastic houses. Acta Hort. (ISHS) 366, 365–372.

Aldrich, R.A., Bartok, J.W., 1989. Greenhouse Engineering. Northeast Regional Agricultural Engineering

Service, Cooperative Extension, Ithaca, NY.

Allen, R.G., Pereira, L., Raes, D., Smith, M., 1998. Crop evapotranspiration guidelines for computing crop water

requirements. FAO Irrigation and Drainage Paper 56. UN-FAO, Rome, Italy.

Baille, A., 1994. Principal and methods for predicting crop water requirement in greenhouse environments. INRA-

CIHEAM, Cahiers Options Mediterraneennes 31, 177–186.

Chaibi, M.T., 2003. Greenhouse systems with integrated water desalination for arid areas based on solar energy.

Doctoral Dissertation. Swedish University of Agricultural Sciences, Alnarp. ISSN 1401-6249, ISBN 91-576-

6438-2.

Chartzoulakis, K., Drosos, N., 1997. Water requirements of greenhouse grown pepper under drip irrigation. Acta

Hort. (ISHS) 449, 175–180.

Eliades, G., Orphanos, P.I., 1986. Irrigation of tomatoes grown in unheated greenhouses. J. Hort. Sci. 61 (1), 95–

101.

Folegatti, M.V., Casarini, E., Blanco, F.F., 2001. Greenhouse irrigation water depths in relation to rose stem and

bud qualities. Sci. Agric. 58 (3), 465-468. ISSN 0103-9016.

Fricke, A., 1998. Influence of different surplus irrigation and substrate on production of greenhouse tomatoes.

Acta Hort. (ISHS) 458, 33–42.

Harmanto, 2002. Water requirement of drip irrigated greenhouse-grown tomatoes in tropical environment. Master

Thesis No. AE-02.2. Asian Institute of Technology, Thailand, unpublished.

Hashimoto, Y., 2000. Plant factory in the 21st century. ICAME 2000 Proceedings of the Third International

Conference on Agricultural Machinery Engineering, vol. I, Seoul, South Korea, pp. 1–13.

Kirda, C., Cevik, B., Tulucu, K., 1994. A simple method to estimate the irrigation water requirement of greenhouse

grown tomato. Acta Hort. (ISHS) 366, 373–380.

Lee, B.W., Shin, J.H., 1998. Optimal irrigation management system of greenhouse tomato based on stem diameter

and transpiration monitoring. Agricultural Information Technology in Asia and Oceania, The Asian

Federation for Information Technology in Agriculture, Suwon, Korea, pp. 87–90.

Papadopoulos, A.P., 1991. Growing greenhouse tomatoes in soil and in soilless media. Agriculture Canada

Publication 1865/E.

Papadopoulos, I., 1992. Fertigation of vegetables in plastic-house: present situation and future aspects. Acta

Horticulturae No. 323. Soil and soilless media under protected cultivation. S, pp. 151–174.

Peet, M., 1995. Sustainable Practices for Vegetable Production in the South. Focus Publisher, Newburyport, MA.

Schulbach, K., Tjosvold, S., Kasapligi, D., 1999. Improving irrigation systems conserves water in greenhouse-

grown cut flowers. Calif. Agric. 53 (2), 44–48.

Schwab, G.O., Fangmeier, D.D., Elliot, W.J., Frevert, R.K., 1993. Soil and Water Conservation Engineering, 4th

ed. Wiley, New York.

Smith, M., 1992. CROPWAT: a computer program for irrigation planning and management. FAO Irrigation and

Drainage Paper 46. UN-FAO, Rome, Italy.

Snyder, R.G., 1992. Greenhouse Tomato Handbook, Publication No. 1828. Mississippi State University,

Cooperative Extension Service, USA, 30 pp.

Soria, T., Cuartero, J., 1998. Tomato fruit yield and water consumption with salty water irrigation. Acta Hort.

(ISHS) 458, 215–220.

Tiwari, G.N., 1996. Controlled environment greenhouse for higher production of vegetables, flowers for Indian

climate conditions. Project Report. Indian Institute of Technology, New Delhi.

Tiwari, G.N., 2003. Greenhouse Technology for Controlled Environment. Narosa Publishing House, New Delhi,

pp. 67–77.

Tiwari, K.N., Singh, A., Mal, P.K., 2000. Economic Feasibility of Raising Seedlings and Vegetables Production

Under Low Cost Plastic Tunnel. International Committees of Plastics in Agriculture (CIPA), Paris, plasti-

culture on-line publication.


Tiwari, K.N., 2000. Annual Report. Plasticulture Development Centre, Agricultural and Food Engineering

Department, IIT, Kharagpur, India.

Tuzel, Y., Ul, M.A., Tuzel, I.H., 1994. Effects of different irrigation intervals and rates on spring season glasshouse

tomato production: II. Fruit quality. Acta Hort. (ISHS) 366, 389–396.

Von Zabeltitz, 1999. Greenhouse Structures, Ecosystems of the World’s 20 Greenhouses. Elsevier, Amsterdam.

Zhou, X., Dong, R., Li, S., Peng, G., Zhang, L., Hou, J., Xiao, J., Zhu, B., 2003. Agricultural engineering in China.

Agricultural Engineering International: The CIGR Journal of Scientific Research and Development. Invited

Overview Paper, August 2003.


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