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Solar Energy

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Heating canarian greenhouse with a passive solar water–sleeve system:Effect on microclimate and tomato crop yield

L. Gourdoa,⁎, H. Fatnassib, R. Bouharroudc, K. Ezzaeria, A. Bazgaoua, A. Wifayac, H. Demratia,A. Bekkaouid, A. Aharounea, C. Poncetb, L. Bouirdena

a Thermodynamics and Energetics Laboratory, Faculty of Sciences, Agadir, Moroccob INRA, University Côte d’Azur, CNRS, ISA, Francec Regional Centre of Agricultural Research, Agadir, MoroccodMechanization Agricultural Department, IAV Hassan II, Rabat, Morocco

A R T I C L E I N F O

Keywords:Solar energyGreenhouse heatingTomatoMicroclimate

A B S T R A C T

Heating greenhouses is indispensable for plant development particularly in winter when air temperature islower. In that sense, passive solar heating is a promising alternative compared to classic methods such as fossilfuels that are cost impacted and harmful to the environment.

The current work is devoted to the study of the effect of a solar heating system using black plastic sleevesfilled with water on the microclimate, tomato yield and the dynamic population of the tomato key pest, Tutaabsoluta (Lepidoptera: Gelechiidae) in canarian greenhouses.

The results show that the use of this heating system, improves the nighttime temperature inside the green-house by 3.1 °C and reduce by 10% the relative humidity compared to the control greenhouse. This microclimateimprovement has a positive impact on the tomato production. It has increased by 35% compared to the controlgreenhouse. It was also noted that the presence of this heating system lead to a decrease in the development thepopulation of T. absoluta in the heated greenhouse.

Based on these results, the solar passive water–sleeve heating system can be an eco-friendly tool to preventintensive use of fuel fossil and negative effect on the environment.

1. Introduction

The main goal of the greenhouse is to provide a suitable micro-climate in order to improve off-season production and to prevent theentrance of key pests such as whiteflies, thrips, Tomato leafminer andothers (Hanafi, 2003). However, in winter season, the greenhousestructure is generally not sufficient to maintain indoor air temperatureat an appropriate level, so heating systems are needed (Sethi et al.,2013).

However, due to rising fossil fuel prices and restrictions on CO2

emissions, an alternative is needed instead of the conventional heatingsystems to ensure plant production in winter.

Solar energy is considered one of the most promising alternative tofossil fuels, the annual solar radiation in Morocco varies between5.28 kWh/m2/day and 6.33 kWh/m2/day. The maximum is received inthe south of Morocco (Mghouchi et al., 2016). It has the advantage ofbeing endlessly renewable and non-polluting energy source (Sethi et al.,2013) and can therefore be used in agriculture to respond to the

increasing social and economic demands that, for reasons of energysaving and the protection of the environment, want to limit the use offossil energy resources.

Recently, several solar systems used to heat greenhouses have beenrecommended by researchers in the world such as rock-bed storage(Kurklu et al., 2003; Gourdo et al., 2018; Jain, 2005), water storage (Duet al., 2012; Bargach et al., 1999; Ntinas et al., 2014), movable in-sulation, ground air collector (Jain and Tiwari, 2003), phase changematerial storage (Berroug et al., 2011; Kern and Aldrich, 1979; Lacroix,1993) and north wall storage (Bourdeau, 1980).

The passive water heating systems is a promising alternative com-pared to classical methods, given their multiple benefits i.e. easy toinstall and low investment cost. Different systems have been reportedunder various cover materials e.g. PE, glass, filon and polycarbonate,and under various greenhouses types around the world (Sethi andSharma, 2008; Santamouris et al., 1994). Nash and Williamson (1978)suggested a 1m3 water tanks blacked out to heat a 30m2 greenhouselocated in Nashville in USA. This system was able to maintain the inside

https://doi.org/10.1016/j.solener.2019.07.004Received 25 October 2018; Received in revised form 9 May 2019; Accepted 1 July 2019

⁎ Corresponding author.E-mail address: lahoucine.gourdo@edu.uiz.ac.ma (L. Gourdo).

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Available online 15 July 20190038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved.

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air temperature 2–3 °C higher than the outside air temperature. Kozaiet al. (1986) tested a water tank heating system filled with 36m3 ofwater, installed in a 856m2

floor area greenhouse located in Tokyo,Japan. It was able to maintain inside air temperature of the greenhouse8–10 °C higher than outside air temperature. As for Govind et al.(1987), they used four 0.8m3 blacked out water drums placed on thenorth side of a 15.4 m2 greenhouse located in Delhi in India. The systemwas able to maintain the inside air temperature 5–6 °C higher than theoutside air, during extreme winter nights in December and January.Dutt et al. (1987) studied water tanks, filled with 1m3 of water, placedon the north side in a 20m2 PE covered greenhouse situated in Delhi(India). Inside air temperature was maintained 3–4 °C higher comparedto outside air conditions on winter nights. Mavrogianopoulos andKyritsis (1993), investigated a transparent polyethylene tubes placed onthe soil in a 200m2 PE covered greenhouse in Athens (Greece). Theaverage minimum temperature was 3–4 °C higher than the outside airand about 1 °C higher than the control greenhouse. Water inside thetubes was circulated at a very low pressure to improve the thermalstorage capacity in the greenhouse (Santamouris et al., 1994). Interiorair temperatures of 3–4 °C higher than the minimum outside air wereobserved. Black steel tanks were also used on the north side of agreenhouse for thermal energy storage (Santamouris et al., 1994). Thissystem was able to maintain the inside air 2–10 °C higher than theminimum outside air temperature. 22m3 of water was stored in blacksteel barrels placed in the north side of 167m2

filon covered green-house located in Flagstaff (USA) where vegetables were grown. Theinside air temperature observed was 13–22 °C higher than the minimumoutside air temperature (Santamouris et al., 1994). Another study car-ried out by Sethi et al. (2003) have tested a galvanized tank placedalong the north side of 21m2 glasshouse located in Ludhuana (India).Nighttime greenhouse temperature increased by 4–5 °C compared tooutside air temperature in December-January 2001. In Table 1, weregroup a summary of the performance of various passive solar green-houses using water storage.

Ntinas et al. (2014) studied a hybrid solar energy system; it con-sisted of a transparent water-filled polyethylene sleeves and two per-forated air-filled polyethylene tubes on the top peripheral sides of it.Above the sleeves and between the two tubes, rockwool substrates wereplaced for hydroponic cultivation of tomato crop; the results of thesesystem sowed that the additional energy provided by the hybrid solarsystem reached approximately 23% during the examined period.

The study presented in this paper falls in this sphere since it focusesthe use of passive heating system based on the principle of storing solarenergy in the water contained in a black plastic sleeves to heat a tomatocanary greenhouse under Moroccan climate. The stored energy comesmainly from solar radiation during the day and used to heat thegreenhouse at night.

Unfortunately, the studies on this matter are scare and concernmore particularly the effect of these passive heating systems on themicroclimate under the greenhouse without being interested in theireffects on the crop yield and the pest dynamics.

To fill in this information gap, this paper discusses the effects of themicroclimate induced by black plastic sleeves on the yield of tomatoand the population of the tomato leafminer T. absoluta (Lepidoptera:Gelechiidae) population, considered as a key pest of the tomato crop inthe Mediterranean basin.

This work cumulates several originalities: (i) The use of blacksleeves that absorb solar radiation unlike other studies that have usedtransparent sleeves. (ii) Study of the effect of this heating system on thetomato yield, plant height and the population of T. absoluta, parametersthat have not been studied in previous studies. This system developed inthis paper can be generalized to the all types of greenhouses and in allclimatic conditions.

2. Materials and methods

2.1. Site and greenhouse description

The experiments were carried out in two similar and independentcanarian greenhouses with metal structures, located in the experi-mental station of the Regional Center for Agricultural Research, thelocal office of the National Institute for Agricultural Research (INRA) insouth of Agadir (30°13 Latitude, 9°23 Longitude, 80 m Altitude), on theAtlantic coast of Morocco. The surface of each greenhouse was 172m2

i.e. 15.6m width by 11m length and a height of 4m at gutter level and5m at span level (Fig. 1). These greenhouses are covered by a 200 µmpolyethylene plastic thermal film (Table 2) and the orientation of itsspans was North-South i.e. perpendicular to the prevailing wind di-rection.

The lateral side openings (two 11m sides and two 15.6 m sides)were 4m – high and were covered with an insect- proof net, used toprevent the intrusion of insects.

The plastic covers were superposed over the insect-proof net on alllateral sides. These lateral plastic covers could be rolled up or down toventilate the greenhouse. The opening side open at 8 am, to evacuateexcess humidity accumulated during the night, and close at 3 pm tolimit exchanges between the air of the greenhouse and the outsideduring the night.

The experimental greenhouse was equipped with a solar water-sleeve heating system, while the control greenhouse was not heated.

2.2. Crop

The crop planted in the experimental and the control greenhouseswas tomato (cv. Solanum lycopersicum L.), planted on January 9, 2017 insoil-less container on a carbonaceous substrate. The planting rows wereoriented north-south, perpendicular to the direction of the prevailingwind. The experimental greenhouse and the control greenhouse werefertigated using the same system; and received the same amount ofwater and fertilizers.

The two greenhouses experimental greenhouse and the controlgreenhouse were fertigated using the same system and received thesame amount of water and fertilizers which is 1.5 L/Plant/Day.

Table 3 summarizes all planting characteristics in the two green-houses concerned.

2.3. Monitoring of the agronomic parameters

In order to estimate the effect of the heating system on the agro-nomic performance, the plant height and number of fruits harvestedwere monitored during the crop cycle. Seven replicates (plants) wereselected randomly in each greenhouse to measure the crop evolution at16, 18, 20, 22, 24, 26, 31, 34, 38, 46, 50, 58, 81, 92, 100, 107, 113,129 days after plantation for plant height and during 5 harvests for thenumber of fruits. The quality of fruits at each harvest and the total yieldat the end of the crop cycle in both greenhouses was compared. Dataanalyses were performed using the SPSS general linear model (GLM) by

Table 1Summary of the performance of various Passive solar greenhouses using waterstorage.

Passive system type Performance Reference

Ground tubes 2–4 °C higher Kyritsis and Mavrogianopoulos (1987)Water tanks 2–3 °C higher Nash and Williamson (1978)Water tanks 13–22 °C > Tair Santamouris et al. (1994)Water barrels 5–6 °C higher Govind et al. (1987)Water tanks 3–4 °C higher Dutt et al. (1987)Water tanks 8–10 °C higher Kozai et al. (1986)Black steel tank 2–10 °C > Tair Santamouris et al. (1994)Water tanks 4–5 °C higher Sethi et al. (2003)Water tubes 3–4 °C > Tair Santamouris et al. (1994)

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SPSS software (IBM SPSS statistics 23) procedure for ANOVA at a levelof P < 0.05). Then, when significance was confirmed, resulting meanswere compared using Newman-Keuls test.

2.4. Monitoring of the population of tomato leaf miner (Tuta absoluta)

The tomato leafminer T. absoluta (Lepidoptera: Gelechiidae) is ahighly destructive pest of tomato crops. The damage caused by this peston tomato can lead 100% crop loss (França, 1993) under weak control.There are several methods to control this pest. The common controlmethod is spraying chemicals products which are very harmful to

humans and environment. The farmers use also the insect-proof nets tokeep out this pest from the greenhouse. The biological control methodsusing natural enemies and biopesticides remain the safest approachesdespite their fairly high cost (Nilahyane et al., 2012). The most effectiveapproach is to combine all the previous methods together with otherslike mass-trapping, cultivar resistant, mulching and management ofclimate inside greenhouse. This strategy is defined as integrated pestmanagement IPM.

The pesticides were sprayed at recommended dosage using sprayerlance. The same equipment was used in both greenhouses (experi-mental and control).

To monitor T. absoluta adults, traps type Delta (containing stickywhite card and T. absoluta pheromone lure trap, Russell IPM, PH-937-1RR, UK) were used. One trap was hanged in the middle of eachgreenhouse (experimental and control) at 1.5 m height. The lures havebeen replaced every 4 weeks in both greenhouses. The traps werechecked weekly and the number of T. absoluta captured was recordedand the results were presented in Fig. 11.

2.5. Description of the passive heating system

The passive heating system is composed of 8 black plastic sleeves,each 32 cm in diameter by 10m in length and 220 µm in thickness(Table 4). Each sleeve is filled with 0.71m3 of water (Table 5). Thesesleeves were placed on the ground and extended on both sides of the 4rows of crops close to their roots (Fig. 2).

The mass of water inside the ducts is heated by infrared radiationabsorbed in the greenhouse during the day. The stored heat is recoveredinside the greenhouse by natural convection and radiation during thenight and used to heat the air inside the greenhouse.

Fig. 1. Diagram representing the experimental and control greenhouses.

Table 2Properties of the polyethylene thermal film used to coverthe greenhouses.

Conductivity 0.41W/mKDiffusivity 0.2991 · 10-6 m2/sSpecific heat 1.383 kJ/kg KThickness 200 µmTransmittance 75%

Table 3Planting characteristics in both the experimental and the controlgreenhouses.

Planting date 09 January 2017Number of rows 4Number of plants/rows 30Inter rows distance 1.30mInter-plants distance 0.3 m

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The characteristics of this water sleeves heating system are sum-marized in Table 5.

2.6. Measurements of different climate parameters

In order to study the influence of the heating system by black waterfilled plastic sleeves, we conducted simultaneous measurements in theexperimental and control greenhouses.

In the experimental greenhouse we measured: the temperature andthe relative humidity of air inside the greenhouse in its center, checkingtwo heights with an HMP50 sensor (HMP50, Campbell Scientific Ltd.,UK). We observed the average soil temperature using a Type E ther-mocouple wire (TCAV-L, Campbell Scientific Ltd., UK) which providesthe soil temperature at 6–8 cm deep and the temperature of the watercontained in the sleeves using a Thermistor (108, Campbell ScientificLtd., UK).

At the same time, in the control greenhouse we measured the insideair temperature and relative air humidity in its center checking twoheights. The soil temperature was recorded using a Type E thermo-couple wire.

In addition to the climatic condition measurements inside thegreenhouses, a weather station was installed outside the greenhouse tomeasure wind speed and direction by an ultrasonic anemometer(WINDSONIC1-L, Campbell Scientific Ltd., UK), the temperature andrelative humidity by an HMP50 probe, the global solar radiation by apyranometer (CMP11, Kipp & Zonen, USA), as well as the averagetemperature of the soil using a TCAV-L sensor.

All these sensors were connected to two data-loggers (CampbellCR3000, Campbell Scientific Ltd., UK) which instantly recorded dataevery 5 s and stored the average values in 10-min time steps on thecomputer and thereafter analyzed.

In Table 6, the characteristics of sensors used in this measurementperiod are shown.

3. Results

3.1. Climatic parameters

Solar radiation, temperature and relative humidity are the mainclimatic parameters that influence plantation development, during themeasurement period; external solar radiation reaches 830W/m2 at12.30 am. Both greenhouses, experimental and control are subjected tothe same external climatic conditions. The solar radiation entering thegreenhouse will increase the air temperature of the greenhouse andheat the water inside sleeves in the experimental greenhouse.

3.1.1. The effect of the heating system on the air temperature and humidityFig. 3 shows the variation of air temperature in both greenhouses

i.e. control and experimental and outside. These data show that thetemperatures inside the greenhouses are always higher than that on theoutside; the temperature difference between the inside of the experi-mental greenhouse and the outside can reach 4.2 °C during the night.During the day, the temperature of the control greenhouse is higherthan that of the experimental greenhouse and the difference can bemore than 1 °C. Conversely, during the night, the air temperature of theexperimental greenhouse is higher than that of the control greenhouse.The temperature difference between both greenhouses is 2.2 °C as anaverage and the maximum is 3.1 °C (Fig. 4).

The heating system with water-filled plastic sleeves operates byabsorbing the incident solar radiation incoming inside the greenhouse,which results in an increase of the water temperature contained in theblack plastic sleeves. At night, or when the greenhouse air temperatureis lower than that of the water in the sleeves, the stored heat is releasedin the internal environment of the greenhouse by natural convectionand radiation, so at night the water can increase the air temperature of

Table 4Properties of the black plastic sleeves.

Conductivity 0.425W/mKDiffusivity 0.3253 · 10-6 m2/sSpecific heat 1.277 KJ/kg KThickness 220 µmTransmittance 4.97%

Table 5Characteristics of the water sleeves heating system.

Volume of water in a row of sleeve 0.71m3

Total volume of water in the sleeves 5.6m3

Sleeve diameter 32 cmThickness 0.25mm

Fig. 2. Internal view of the experimental greenhouse (A), and the control greenhouse (B).

Table 6Characteristics of the sensors used in this experiment.

Description Sensors Unity Accuracy

Air temperature Vaisala HMP50 °C ± 0.6 °CRelative humidity Vaisala HMP50 % ±3%Water temperature 108 °C ± 0.2 °CSoil temperature 108 °C ± 0.2 °CWind speed WINDSONIC1-L m/s ± 0.001m/sWind direction WINDSONIC1-L Degree ± 1°Net radiation CNR4 W/m2 <1%Global solar radiation Pyranometer Kipp&zonen

CMP11W/m2 ±0.2%

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the greenhouse and in the same time the water will be cool, This coldwater will refresh the greenhouse air during day time.

Fig. 5 shows the variation of the air relative humidity inside theexperimental greenhouse, the control greenhouse and on the outside. Itwas found that during the night the air relative humidity of the outsideis always higher than the relative humidity in the experimental and thecontrol greenhouses.

During the night, the relative air humidity is higher in the controlgreenhouse compared to the experimental one. The difference in hu-midity between the two greenhouses exceeds 10%. This difference inhumidity between the experimental greenhouse and the controlgreenhouse is due to the presence of the heating system. RelativeHumidity varies according to temperature changes: it increases if thetemperature drops and decreases if it rises. As the heating system has

Fig. 3. Variation of the air temperatures inside the experimental greenhouse, the control greenhouse and on the outside.

Fig. 4. An amplified view of a night part of a day.

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increased, the air temperature of the experimental greenhouse by 3.1 °Ccompared to the control greenhouse, its relative humidity will decreaseand it will be lower than that of the control greenhouse.

During the day, the relative humidity of the two greenhouses wassimilar, and reach minimums of 20% at 2 pm. This is due to the fact thatthe side openings were rolled up during the day to evacuate the excesshumidity in the greenhouses, and avoid condensation.

3.1.2. Water temperature inside the plastic sleevesFig. 6 shows the evolution of the water temperature inside the

sleeves over time. It is observed that the temperature of the water insidethese sleeves reaches its maximum of 34.7 °C at 4.10 pm, while the peakof air temperature inside the greenhouse reaches a maximum of 38.4 °Cat 2.30 pm (Fig. 4).

During the day, the water stored a quantity of energy equal to:

=Q mc TΔP (1)

where m is the water mass in the sleeves; equal to 5600 kg; cp is thespecific heat of water 4180 J/kg K and ΔT is the water temperaturedifference between day and night.

This energy will be restored to heat the air in the greenhouseovernight.

The water temperature reaches a minimum value of 16.5 °C at8.10 am, while the inside air temperature of the greenhouse reaches itsminimum value of 9.5 °C at 6.30 am.

During the experiment period, from January 9 to May 2, 4914 kWhof energy was released by the solar water –sleeve system. This energywas used to heat the greenhouse in order to provide optimal tempera-ture for crop growth. To produce this energy by conventional heatingsystems based on fossil energies, 386.9 kg of butane would be required.As 1 kg of butane releases 3.02 kg of CO2, this ecofriendly heatingsystem was able to reduce 1168.5 kg of CO2 during the test period.

3.1.3. Effects of the heating system on the soil temperatureFig. 7 shows the variation of the soil temperature of both

greenhouses (experimental and control). By analyzing this graph, weobserve that during the day the soil temperature in the control green-house is slightly higher than the soil temperature in the experimentalgreenhouse. This is due to the solar radiation absorption in the water-filled sleeves. At night, the soil temperature of the experimentalgreenhouse is higher than that of the control greenhouse, this is causedby the heat that was stored in the water during the day and released atnight in the greenhouse. This freed heat in the greenhouse contributesto warm up the soil.

3.2. Effects of the heating system on the agronomic parameters

We have selected 24 plants in each greenhouse. These plants arespread over 4 rows (6 plants per row). We measured the height, thefruit quality and the yield of each of the 24 plants selected.

3.2.1. Plant heightFig. 8 shows the evolution of the average height of the plants in both

experimental and control greenhouses. While comparing the twocurves, we noted that the mean crop height in the experimentalgreenhouse is higher than in the control greenhouse and differed 50 cmat the fifth harvest. The increase of air temperature in the experimentalgreenhouse compared to the control greenhouse influenced the plantheight, as well as the number of bouquets (two more bouquets in theexperimental greenhouse).

3.2.2. Total yieldBy comparing the tomato production in the two greenhouses, we

observed that the yield from the greenhouse equipped with the passiveheating system is 35% higher than in the control greenhouse. Thisperformance in yield was due to the improvement of the microclimateunder the greenhouse given the better conditions for the developmentof tomato crop. We have selected 24 plants in each greenhouse, wemeasure the yield of each one, and then we calculate the average. Thisaverage is multiplied by the total number of plants in the greenhouse;

Fig. 5. Variation of the relative air humidity inside the experimental greenhouse, the control greenhouse and on the outside.

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the total weight harvested in the two greenhouses during the experi-mentation period is represented in Fig. 9.

The researches related to the heating effect on tomato productionare scarce in the literature. Among these research studies, we can foundthose of Canakci and Akinci (2006) who reported the beneficial effectofheating on tomato.

This positive effect of the solar heating system on production yieldwas also reported by Bargach et al. (2004), who found an improvementof 20 g/plant on the melon yield using a heating system with the samethermal energy storage mode. In a separate study in Agadir region,Bazgaou et al. (2018) show that the rock-bed heating system is able toimprove the tomato yield by 29%. Gourdo et al. (2019) for their part

Fig. 6. Variation of the water temperature inside the sleeves.

Fig. 7. Measured soil temperature in the experimental and control greenhouse.

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find that the rock-bed heating system installed under the ground of thegreenhouse improve the tomato yield by 22%.

3.2.3. Fruit qualityThe harvested fruits were grouped into seven sizes according to

agronomist standards from the largest to the smallest size: out of size(> 84.78mm), size 1 (76.1 mm < diameter < 84.78mm), size 2(66.8 mm < diameter < 76.1 mm), size 3 (55.7mm < diameter <66.8 mm), size 4 (45mm < diameter < 55.71mm), size 5(< 45mm) and wasted fruits.

Fig. 10 shows the percentages of tomato fruit sizes, which wereharvested in both experimental and control greenhouses. We observedthat for the experimental greenhouse size 1 is the most dominant,whereas in the control greenhouse size 2 is the most dominant. Soclearly the heating system with water-filled plastic sleeves has a verypositive effect on the quality of tomato production.

3.3. Dynamics of T. Absoluta population

T. absoluta is considered as a key pest of tomato. It can cause lossesof up to 80–100% on tomatoes. The larvae are the harmful stage of thetomato leaf miner life cycle.

Fig. 11 shows the dynamics of T. absoluta population in both theexperimental and the control greenhouses. Analyses of the data of thepheromone traps installed in the greenhouses revealed that the numberof T. absoluta was relatively low in the greenhouse equipped withpassive heating system compared to the control greenhouse.

It should be noted that the number of trapped T. absoluta individualsvaried from 01 to 80 in the control greenhouse and between 0 and 25 inthe experimental greenhouse. From March 27, 2017, the number of T.

Fig. 8. Evolution of plant height in the experimental and control greenhouses.

Fig. 9. The tomato yield in the control and experimental greenhouses.

Fig. 10. The percentage of each size of tomato fruits in the control and ex-perimental greenhouses (out of size (do > 84.78 mm), size 1 (76.1 mm <d1 < 84.78mm), size 2 (66.8 mm < d2 < 76.1 mm), size 3 (55.7 mm <d3 < 66.8 mm), size 4 (45mm < d4 < 55.71 mm), size 5 (d5 < 45mm)).

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absoluta increased rapidly in both greenhouses due to the massive po-pulation of this pest outside of the greenhouses. The climate in thecontrol greenhouse is more favorable to the development of this pest. Ingeneral, it appears that the presence of water sleeves has a negativeeffect on the development of T. absoluta. This reduction was very sig-nificant and a total of 100% reduction was recorded, especially at thebeginning of the cycle until March 06, 2017. This reduction rate de-creased after March 20, 2017 and did not exceed 69%. The populationdynamics is defined as the aspect of population ecology dealing withforces affecting changes in population densities of affecting the form ofpopulation growth. In fact Larsson (1989) and Wallner (1987) havedescribed all factors affecting insect population dynamics which in-cluding among others the climatic parameters. Since this solar passivesystem (water sleeves) increase the temperature and decrease the re-lative humidity our study was also focused on the impact on the dy-namic of T. absoluta population as a key pest of tomato crops undergreenhouse. Krechemer and Foerster (2015) have reported that tem-perature affect inversely the longevity of both males and females of T.absoluta which means the shortness life of adults. Consequently, thelower population of T. absoluta adults and damage observed on tomatocrop and fruits could be explained by the impact of temperature in-crease in the experimental greenhouse.

4. Discussion

This system of heating by black plastic sleeves filled with waterinstalled in the greenhouse allows increasing the air temperature duringthe night; this is due to the heat stored in the water sleeves during theday and released into the greenhouse by radiation and convection.

At night the water transfers heat by convection to the greenhouseair which will reduce the water temperature inside the sleeves. Thiscold water will refresh the greenhouse air during day time.

This passive heating system allows also increasing the air relativehumidity of the greenhouse during the day and lowering it at night.

Water-sleeve system creates favorable conditions for the good plantdevelopment (top temperature and humidity range) which positivelyinfluence the yield, plant growth and the size of the fruits. On thecontrary, very low temperatures slow down plant development and

reduce the absorption of water and mineral salts by the roots (Calvert,1957, Hussey, 1965; Heuvelink, 1989). This is in agreement with theresults found by Gourdo et al. (2019), Bazgaou et al. (2018), Verkerk(1955), Hurd and Graves (1985) and Adams et al. (2001) who foundthat the improvement of night temperature has a very positive effect onthe growth, fruit size and development of tomato fruits.

The effect of heating system used in the current work on the de-velopment of T. absoluta can be explained by the low relative air hu-midity generated by such system inside the greenhouse. This findinghas also been reported in some previous studies and confirms that lowerrelative air humidity reduces the number of eggs produced by females,shortens the life span and reduces the number of T. absoluta adults(Uchoa-Fernandes et al., 1995; Miranda et al., 1998; Guimapi et al.,2016; Cuthbertson et al., 2013).

The negative effect of the heating system on T. absoluta could alsobe explained firstly by the compensation of plant growth speed (higherin the experimental greenhouse) compared with the damage caused bythis pest i.e. more the plant growth is higher more the injury is in-visible. In the other hand, the tomato leaf volatiles have an effect on theflight behaviour, attraction and oviposition of T. absoluta (Proffit et al.,2011). These volatiles are classified as secondary metabolites whichdepend especially on the climatic parameters and environment(Karppinen et al., 2016; Sampaio et al., 2016). More studies should beplanned to investigate the chemical components involved in this phe-nomenon under passive heated greenhouses.

Emphasis has been placed on the climatic and agronomic perfor-mances to evaluate our heating system. By comparing the climatic andagronomics results of our passive heating system to those studied byother researchers, this system was observed to be more efficient com-pared to those using transparent tubes placed between the crop rows(Mavrogianopoulos and Kyritsis, 1993; Sethi and Sharma, 2008). Con-versely, our system is less efficient than that using barrels filled withwater set up in the north side of the greenhouse (Sethi and Sharma,2008). However, the disadvantages of the latter system are that it canbe set up in small greenhouses and the heat released by this system isnot distributed evenly in the greenhouse.

The passive heating system developed in our study did not achievethe performance of the conventional boiler heating systems (Bargach

Fig. 11. The number of T. absoluta trapped each week in the experimental greenhouse and in the control greenhouse.

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et al., 1999; Bouadila et al., 2014) that can cover 100% of the heatingneeds of the greenhouse. Despite this lack of performance, the passivesystem has the advantage of being environmentally friendly andcheaper compared to the conventional systems operating with fossilfuels. In fact, the conventional boilers, are expansive and their con-sumption of energy can reach up to 1 L of fuel/m2/year (Attar et al.,2013).

To improve the efficiency of the passive solar heating system it isnecessary to increase the volume of water used to store energy insidethe greenhouse during the day. However, the diameter of the sleevesused must not exceed 32 cm, in order to not hinder the circulation ofmachines and workers between crop rows. To overcome this dilemma,more research must be carried out on other heat exchange fluids inorder to increase the energy released in the greenhouse during thenight.

5. Conclusion

The heating system studied in this paper has improved the insidemicroclimate of a canarian greenhouse. It allowed an increase in airtemperature by 3.1 °C, and a reduction of air relative humidity by 10%.This improvement of the greenhouse microclimate favored the plantgrowth and improved the quality of tomato production as well as itsyield.

This passive heating system will probably have a positive effect interms of reducing the risk of the disease development on plants, due tothe lowering of air relative humidity inside the greenhouse.

This heating system, using black plastic water-sleeve, is a eco-friendly system based on renewable resources and has the advantage todistribute the heat evenly to the plants. This system is more efficientcompared to the heating systems using transparent ducts studied byother researchers. However, despite these advantages, their power isnot as efficient as the conventional heating systems using fossil fuels. Infact, sometimes, the stored solar energy alone cannot meet the totalheating requirements in the greenhouse. For this reason, other heatexchange fluids, that are capable of meeting these needs, must be in-vestigated.

Acknowledgements

This work was supported by the National Center for Scientific andTechnical Research (CNRST) in Morocco, within the project “PPR56/2015”.

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