| Set-up
of greenhouses:
Based
on the experience and experiments of
von Zabeltitz the greenhouse for the experimental set-up has been
designed (s. fig. 1). The greenhouses have large ventilation openings
at the side walls and gables. An additional opening is placed at the
ridge. The ratio of ventilation area to ground area is about 1.1.
Additionally two fans are installed in the gable for emergency
ventilation. An Indian greenhouse company has been selected to build up
14 greenhouses for the central experiment (8) and for the satellite
experiments (6). The preparation of the area at AIT campus, the
foundation and the infrastructure were carried out by Prof. Salokhe,
AIT. Due to the engagement of Prof. Salokhe the experimental set up
could be finished within a few month.
 |
| Fig. 1.: Sketch
of the screened experimental greenhouse in Bangkok |
Besides
these 14 experimental greenhouses
three smaller greenhouses were build up by Prof. Salokhe for comparison
of different insect screens with different mesh sizes. The results of
these measurements were necessary to decide, whether greenhouses in the
CE could be covered with insect screens against Thrips.
Insect
screens:
Laboratory
measurements of spectral
transmissivity of screens and plastics were carried out at the
Institute of Horticultural and Agricultural Engineering, University of
Hannover. This was followed by measurements of air transmissivity
(discharge coefficients) of screens using a wind tunnel apparatus at
the same institute. 15 different insect screens were tested for their
air permeability and light transmission, and the results were
evaluated. The thickness of the threads and meshes were measured under
a microscope. The screens came from the Netherlands (10), Israel,
Germany and Thailand.
The air permeability was measured with an apparatus consisting of a
wind tunnel with a fan at one end. The tunnel was connected to a wooden
box (2x2x2 m), open at one side. The screens to be tested were attached
to a frame, which was then fixed within the opening. The dynamic
pressures were measured for each screen, at different air velocities,
with an inclined tube manometer (connected with a measuring rake to the
wind tunnel). The pressure difference between the static pressure
behind the screen and the room atmosphere was measured with a
“Betz-Manometer”. For the measurements, the pressure was regulated at
the “Betz-Manometer” by increasing the air velocities in steps of 0,05
and 0,01 for each screen. This was done for a better comparison of the
screens later on. The measurements were taken four times for each
screen, and a mean value was computed from these values.
The results of the preparatory measurements in the small greenhouses,
build by Prof. Salokhe, have shown that with decreasing mesh size
temperature will be increased. As the measured temperature increase was
small, the originally open greenhouses of the CE were covered with 78
mesh insect screens (s. P1)
against Thrips.
External
and greenhouse climate measurements
were made at the AIT campus in Bangkok, Thailand in the greenhouses of
the CE and in one satellite greenhouse. The internal climate
measurements were carried out concurrently in similar, naturally
ventilated greenhouses covered with three different insect-proof
screens on ventilation openings. The different nets are 22 x 52 mesh
(34-mesh); 40 x 37 mesh (40-mesh, Econet M); and 52 x 78 mesh (78-mesh,
Econet T). Tomato (Lycopersicon esculentum, cv. King
Kong II)
plants were grown in the greenhouses during the experimental period.
The results show that the inner temperature will be increased in line
with the higher net size covered on the greenhouse. The temperature
difference was only occurred at the day time. The greenhouse with
78-mesh had around 1-2 °C (on average) higher than the greenhouse with
40-mesh. The air temperature could reach up to 37 °C at the day time.
Similarly, the greenhouse with 40-mesh had 1 - 2 °C (on average) higher
than the greenhouse with net of 34-mesh at the day time. The air
temperature inside the greenhouse with 34-mesh had the lowest
temperature compared to the other greenhouses. In general the overall
temperature inside the greenhouse in this season is ranging between 25
to 37 °C.
Crop growth factors such as Leaf area Index (LAI) and floor use
fraction were estimated during the experimental periods. The daily
water balance is an important parameter which is strongly influenced by
the physical properties of a greenhouse such as: ventilation rate, air
exchange rate. Based on the daily water balance, the
evapo-transpiration efficiency, water requirement for irrigation and
air exchange rate can be calculated. Two water flow meters were
installed on both the irrigation inlet pipe and the drainage canal.
Prior to use, the meters were calibrated. In the other two greenhouses,
the measurements of evapo-transpiration were made manually.
A dynamic mass and energy balance model of the greenhouse system was
developed in Matlab/Simulink in order to predict the internal
micro-climate of the greenhouse and evapo-transpiration from external
climatic data and the properties of insect screens. The model is based
on several physical and empirical relationships obtained from
literature. Use of Simulink enables the determination of the various
states of the system using a set of differential equations, in a
holistic manner.
Model predictions of greenhouse air temperature, relative humidity and
evapo-transpiration were compared to the measurements from the two
greenhouses and good agreement was achieved. Scenario simulations were
then carried out to predict the effect of a range of insect-proof
screen parameters on greenhouse air temperature. Simulations were also
carried out to predict the greenhouse air temperature from external
climate parameters for different seasons of the year. The results form
a good basis for decisions on screened greenhouse design improvements
and climate control interventions in screened greenhouses in the humid
tropical climates.
When evaluating these results, one can consider that the design of the
greenhouses with a large ventilation opening (ratio of ventilation
opening to ground area > 1.0) is already well adapted to the
tropical climate conditions in Bangkok. The transpiration rate of the
crop has a significant influence on the greenhouse climate.
Nevertheless there are still problems with fruit set, Ca-deficiency and
fungi infestations (s. results of P2,
P3 and P4).
At KU-campus Kaempaensaen experiments were carried out in an empty
greenhouse with fan and pad cooling, supported by NRC. In this
greenhouse the temperature and humidity distribution was measured. The
results are showing severe gradients from the pads to the fans. The
temperature is increasing and the humidity is decreasing. Due to these
results, it is doubtful whether fan and pad cooling is an alternative
to a greenhouse with free ventilation. These experiments must be
repeated with a tomato crop inside the greenhouse.
Irrigation
System:
The
set-up of the irrigation and
fertilisation system was planned by Prof. Salokhe, AIT. Due to the pour
quality of natural soil at AIT campus it was necessary to grow the
tomato plants in pots with a standardised substrate. Consequently,
subsoil irrigation was not possible. The pots are irrigated with drip
irrigation. The system has been prepared for a closed irrigation system
with gutters in the soil covered with PE-plastic film, but due to the
expected problems with recycling of the irrigation water, the drainage
water was released to the clong.
For fertilization Dosatron fertilizer injectors were installed for each
greenhouse. However due to problems with Ca-supply, it was necessary to
install a second Dosatron in order to inject CaNO3
separately from other fertilizers (s. P2).
Initially there were severe problems with malfunctioning of Dosatrons
but after exchanging the mechanics, the Dosatrons became more reliable.
Effects
of UV absorbing plastic films on greenhouse whitefly Trialeurodes
vaporariorum:
In addition, the effect of plastic films
on
the dispersion behaviour and the effect of the quantity of UVA portion
of the UV spectrum on greenhouse whiteflies has been investigated at
Hanover campus. Two plastic films, (Thermilux (a standard agricultural
film and UV transmitter), and K Rose (UV blocking)) with different
spectral transmissivity characteristics for UV radiation were used to
cover small tunnel. A cross-like structure comprising of four tunnels
(two of which were covered with Thermilux and two with K Rose plastic
film), and a black box compartment at the centre, was constructed and
used in this experiment. Whiteflies were released from the black box
compartment and allowed to fly in to a tunnel of their choice. The
whiteflies were later recaptured using yellow sticky traps placed at
specific distances inside the tunnels. Initial results indicate that
more whiteflies (over 90 %) were recaptured in the tunnels covered
using the UV transmitting plastic film. Whitefly penetration into the
tunnels was more in the tunnels covered with Thermilux plastic film.
Penetration in to the tunnels covered with K Rose plastic film was
limited as manifested by the large number of whiteflies recaptured on
the first trap (96 %) and the few numbers recaptured on the last traps
(0.3 %). However, the inclusion of plants inside the tunnels did not
change the penetration behaviour of the whiteflies in either of the
materials. Therefore UV absorbing plastic films may be incorporated in
integrated pest management programs in greenhouses.
Back to content
|
|
 | Ajwang,
P., Tantau, H.-J. (2008) : A Simulation Model for Functional Design of
Insect-Proof Greenhouses for the Humid Tropics. European Journal of
Horticultural Science, (submitted).
ABSTRACT
A
simulation model based on energy and mass balance method was developed
in MATLAB\SIMULINK in order to predict the effect of insect-proof
screen properties on climate in naturally ventilated greenhouses in the
humid tropics. The model uses the four commonly measured weather
parameters (wind speed, global solar radiation, air temperature and
relative humidity) as input variables The model was used to evaluate
the effects of discharge coefficients (Cd) and area of insect-proof
screen materials on greenhouse climate. The discharge coefficients of
the insect-proof screening materials were determined by relating static
pressure drop and airflow rates using the Bernoulli and continuity
equations. External and greenhouse climate measurements were made at
the Asian Institute of Technology (AIT) campus in Bangkok, Thailand.
The internal climate measurements were carried out concurrently in two
similar, naturally ventilated greenhouses covered with different
insect-proof screens on ventilation openings. Tomato (Lycopersicon
esculentum ‘King Kong II) plants were grown in the greenhouse during
the experimental period. Model predictions of greenhouse air
temperature were then compared to the measurements from the two
greenhouses and good agreement was achieved. The results form a good
basis for decisions on screened greenhouse design improvements and
climate control interventions in screened greenhouses in the humid
tropical climates.
| | Max, J. F.; Horst, W. J.; Mutwiwa, U. N.; Tantau, H.-J. (2008).
Effects
of Greenhouse Cooling Method on Growth, Fruit Yield and Quality of
Tomato (Solanum lycopersicum L.) in a Tropical Climate. Biosystems
Engineering, (submitted).
ABSTRACT
A tomato
(Solanum lycopersicum L.) crop was grown in four greenhouses (GH’s)
during the dry season 2005/06 in Central Thailand. Sidewalls and roof
vents of two GH’s were covered with nets and these GH’s were
mechanically ventilated when air temperature (T) exceeded 30 °C
(“NET”). The other two GH’s were clad with polyethylene film and
equipped with a fan and pad cooling system (“EVAP”). Overall mean T was
significantly reduced by 2.6 and 3.2 °C (daytime) and 1.2 and 2.3 °C
(night) in EVAP as compared to NET and outside air, respectively. T
maxima in EVAP averaged about 4 °C lower than in NET and outside. The
relative humidity (rH) was around 20 and 30 % (day) and 10 and 15 %
(night) higher in EVAP than in NET or outside, respectively. Vapour
pressure deficit averaged 0.25 in EVAP, 1.03 in NET and 1.48 kPa
outside. The crop water-consumption was significantly lower in EVAP
(1.2) than in NET (1.8 L plant-1 day-1), which is ascribed to reduced
transpiration in EVAP. Total fruit yield was similar in NET (6.4) and
EVAP (6.3 kg plant-1). Although the quantity of undersized (mostly
parthenocarpic) fruits was reduced in EVAP, the proportion of
marketable yield was significantly higher in NET (4.5) than in EVAP
(3.8 kg plant-1), owing to a largely increased incidence of fruit
cracking in EVAP. This coincided with higher fresh weight and Ca
concentration in the fruits but reduced Ca concentrations in vegetative
plant parts in EVAP. From the results and considering the costs for
installation and operation, it is concluded that in regions with high
atmospheric rH evaporative cooling is not recommendable without
profound technical modifications.
| | Patil, S. L., Tantau, H. J., Salokhe, V. M. (2007).
Modelling of Tropical Greenhouse Temperature by Auto Regressive and Neural Network Models. Biosystems Engineering. Accepted.
ABSTRACT
In
this study the variation of inside air temperature in a tropical
greenhouse was investigated. The study included auto regressive (AR)
model with an external input (ARX), an auto regressive moving average
model with an external input (ARMAX) and a neural network auto
regressive model with an external input (NNARX). External and internal
climatic data recorded over a year were used to build and validate
models for simulating environmental conditions inside the greenhouse.
The variables measured to estimate the greenhouse internal climate
included external temperature, solar radiation, relative humidity and
cloud cover. It was observed that models performed better when series
tuning was done for fixed temperatures rather than fixed during time.
Though ARX outperformed ARMAX, NNARX predicted results were in close
agreement with the measurements.
| | Mutwiwa, U. N., Max, J., and H. J. Tantau
(2007).
Effect of Greenhouse Cooling Method on the Growth and
Yield of Tomato in the Tropics.
ABSTRACT
Cooling greenhouses in the humid tropics is especially challenging due
to the high intensity of solar radiation and humidity prevalent in
these regions. The effect of natural ventilation and evaporative
cooling on the greenhouse microclimate, growth and production of tomato
Solanum lycopersicum cv FMTT260 were evaluated. The research was
carried out in two greenhouses (measuring 20 m long by 10 m wide) at
the experimental site of the “Protected Cultivation Project” on the
campus of the “Asian Institute of Technology” (AIT), situated 44 km
north of Bangkok in Khlong Luang, Pathum Thani, central Thailand, (14°
04’ N, 100° 37’ E, altitude 2.3 m). The naturally ventilated greenhouse
was covered with a UV-absorbing plastic film on the roof and a 50-mesh
insect proof net on the sidewalls and roof ventilation opening. The
evaporative cooled greenhouse was completely covered with the
UV-absorbing plastic film and was equipped with a fan and pad cooling
system. In each greenhouse, 300 tomato plants were grown at a density
of 1.5 plants m-2 and maintained for 15 to 20 weeks. Results from two
seasons show that the cooling method influenced the greenhouse
microclimate, plant growth and yield. Although evaporative cooling
lowered greenhouse temperature, the unwanted increase in humidity
resulted in fungi infections and reduced transpiration. Plants grown in
evaporatively cooled greenhouse were 30 cm to 45 cm shorter than those
grown in naturaly ventilated one. Differences were also noted in
flowering, leaf area, dry matter partitioning and harvested yield. The
significance of cooling method and greenhouse covering material on
plant growth and production in protected cultivation systems in the
tropics is discussed.
|
| Mutwiwa, U. N., von Elsner, B., Max, J.,
and, H. J. Tantau (2007)
Cooling Naturally Ventilated
Greenhouses in the Tropics by Near-Infra Red Reflection
Paper accepted for presentation during the High Technology for
Greenhouse System Management conference (GREENSYS2007) to be held from 4th
to 6th October 2007, in Naples, Italy. Accepted for publication in Acta Horticulturae.
ABSTRACT
High air-temperature and -humidity inside greenhouses located in the
semi-humid and humid tropics is one of the major constraints to
protected cultivation in areas such as central Thailand. Studies were
conducted during the dry and rainy seasons in two naturally ventilated
greenhouses, clad with insect-proof nets on the sidewalls and roof
ventilation openings, to investigate the effect of a newly developed
shading paint containing a near infra red (NIR) reflecting pigment on
the greenhouse microclimate and plant growth. A polyethylene film was
used to cover the roof and gable of the greenhouse. Mulching material
was a white plastic film. The shading paint was applied on the roof of
one of the greenhouses (“Trt”) using a high pressure system. This led
to a lowering of the greenhouse air temperature by a maximum of 4 °C
when the crop was young corresponding to 18% reduction in transmission
of global radiation. However, due to the cooling effect of the
transpiring crop, temperature differences between the greenhouses
levelled out when the crop was mature. Shading reduced plant water
requirement, power consumption of the fans, the number of blossom-end
rot affected and parthenocarpic fruits, in both dry and rainy season. A
slight reduction in marketable yield and an increase in the number of
cracked fruits were observed in Trt. Although there is need for more
research, these results reveal that combination of natural ventilation
and NIR-reflection may provide a solution for cooling greenhouses in
areas with high ambient humidity levels.
|
| Mutwiwa, U. N., Tantau, H. J., von Elsner
B., and J. Max (2007)
Effects of NIR-Reflection Greenhouse
Cooling on Blossom-End Rot and Fruit Cracking in Tomato (Solanum
lycopersicum, L.)
Proceedings of the 6th workshop on Sustainable
Horticultural Production in the Tropics held from 6th
to 9th December 2006 at Mtwapa, Kenya. Accepted for publication in African Journal of Horticultural Science.
ABSTRACT
Blocking the near infra red (NIR) portion of the global radiation from
entering a greenhouse is one of the emerging environmentally friendly
and economical ways of reducing greenhouse temperature without
increasing the humidity. In this study, the effect of cooling
greenhouses by NIR-reflection on the microclimate, fruit quality and
growth of tomato crop was investigated. Two greenhouses measuring 10 m
long by 20 m wide by 6m high were constructed at the Asian Institute of
Technology, Klong Luang, Thailand. Both greenhouses were naturally
ventilated and were clad using insect proof screens (78-mesh) on the
sidewalls and ventilation openings while the roof was covered with an
ultra violet (UV) absorbing plastic film. Reduheat, a NIR-reflecting
pigment was applied on the roof of one of the greenhouses (Trt).
Results show that the quantities (both weight and count) of tomato
fruits affected by blossom-end rot (BER) as well as undersized fruits
(weighing less than 50 g) during both, dry and rainy seasons were lower
for the plants grown inside the greenhouse with the NIR-reflecting
pigment on the roof. On the other hand, in this greenhouse the number
of cracked fruits was slightly higher. In addition, NIR-reflecting
pigment reduced electric power consumption of the ventilation fans
(used for emergency cases). The application of NIR-reflecting pigments
on greenhouse covers for cooling, reduction of water requirement and
fruit quality improvement is recommended for crops grown inside
greenhouses when solar radiation is in abundance.
|
| Mutwiwa, U. N., Tantau, H. J., Salokhe, V.
M., and U. Schmidt (2007)
Phytomonitoring Transpiration of
Tomatoes Grown in Naturally Ventilated Greenhouses in the Humid Tropics
Proceedings of the 5th International Symposium
of Irrigation of Horticultural Crops to held in Mildura, Australia,
from 28th August to 2nd
September 2006. Accepted for publication in Acta Horticulturae.
ABSTRACT
Naturally ventilated greenhouses in the humid tropics require large
ventilation openings in order to provide sufficient air exchange, hence
lower temperature and humidity levels, and increase carbon dioxide
concentration inside the greenhouse. Fixing insect proof nets in front
of the ventilation openings is becoming increasingly popular as it
reduces the entry of insect pests into the greenhouse thereby
minimising the usage of pesticides. However, insect proof screens also
reduce airflow into and out of the greenhouse thus affecting the
bioclimate. The effect of insect proof screens on the transpiration of
tomato crops was investigated in large experimental greenhouses in
Bangkok, Thailand. Online monitoring of the bioclimate was done in two
greenhouses covered with insect proof screens with different physical
properties, using a plantputer phytomonitor. In addition,
evapotranspiration of the tomato plants was also determined using the
water balance method. White mulches and white pots were used in the
greenhouses to reduce the solar radiation load. Results show that leaf
transpiration (and crop water requirement) was higher in the greenhouse
clad with the finer mesh, when the plants were young (6 WAT) but the
opposite was observed for mature plants (14 WAT), though the difference
was not statistically significant. Vegetative (plant height, leaf area
index) and generative (number of trusses, yield) plant growth was not
significantly affected by the porosity of the net. Moreover the results
show that phytomonitoring technique provides the greenhouse manager
with online plant response hence decisions on climate (and nutrition)
control can be taken earlier than is the case when relying on visual
inspection.
|
| Mutwiwa, U. N., Tantau, H. J. and Salokhe V.M.
(2007)
Greenhouses in the Humid Tropics: Problems and
Solutions.
Proceedings of 3rd International Conference on
Solar Radiation and Day Lighting (SOLARIS 2007) February 7th
to 9th, 2007, New Delhi, India. Vol. 1: 238-247.
ABSTRACT
The development of a greenhouse suitable for protected cultivation in
the humid tropics is still far from being realized. Reducing the heat
load without increasing the humidity inside the greenhouse, pest
exclusion without heavy reliance on chemicals and monitoring plant
response to changes in the microenvironment are the main challenges. As
such the development of a strategy that allows for rational use of
resources for high quality plant production while ensuring maximum
protection and sustainability of the environment is still being sought.
The progress made in developing an adapted greenhouse that encourages
biological pest control and simultaneously offers an optimum
microclimate is discussed in the concept of integrated plant production
in the humid tropics.
|
| Harmanto, H.J. Tantau and V.M. Salokhe
Microclimate and Air Exchange Rates in Greenhouses covered with
Different Nets in the Humid Tropics
Biosystems Engineering (2006) 94 (2), 239-253
ABSTRACT
The effect of different mesh sizes of nets (40, 52 and 78 mesh) to
cover ventilation openings of greenhouses located in the humid tropics
on microclimate and air exchange rates was studied. Experiments were
carried out in three identical greenhouses (each size of 10m wide by
20m long). These greenhouses were covered with a plastic film on the
top, and different insect-proof nets on the roof and sidewalls,
respectively. Water vapour, transpired from 300 tomato plants
cultivated in each greenhouse, was used to determine air exchange rate.
In addition, an energy balance method, based on solar radiation and
daily microclimate in and outside the greenhouse, was used to predict
the air exchange rate. A good agreement was achieved between the
measured and predicted air exchange rates. Results show that the use of
nets at different mesh sizes had a significant effect on microclimate
and air exchange rate. Compared to the 40 mesh greenhouse, the
reduction of air exchange rate of about 50% and 35% was obtained for
the 78 and 52 mesh greenhouses, respectively. Consequently, the
internal air temperature was also increased by 1-3 1C. Regarding air
temperature rise, only minor differences have been observed due to very
large ventilation openings. However, differences in absolute humidity
were much more pronounced and statistically significant. Humidity in 78
mesh greenhouse was consistently approx. two times higher than 40 mesh
greenhouse, while 50% increment was observed in the 52 mesh greenhouse.
Based on internal microclimate and its ability to exclude some major
insects, the 52 mesh net seems to be selected as a compromise size of
nets appropriate for tropical greenhouse.
| | Harmanto, H.J. Tantau and V. M. Salokhe (2006)
Optimization of Ventilation Opening Area of a Naturally Ventilated Net
Greenhouse in Humid Tropical Environment
International
Symposium on Greenhouse Cooling, ISHS, Almeria, Spain, Acta
Horticulturae 719, 165-171.
ABSTRACT
A
study was conducted to evaluate the performance of a naturally
ventilated net greenhouse designed for humid tropical conditions having
a large vent ratio of 1.05. The greenhouse had a size of 10 m by 20 m.
An ultraviolet (UV)-stabilized plastic film was used to cover the roof,
gables and lower parts of the walls. The ventilation openings in the
roof and side wall were covered by UV-absorbing insect-proof screen
(52-mesh). Maintaining a very large ventilation opening, however, is
not always advantageous when the cost of nets and the possible
migration of smaller pests into the greenhouse via the net are taken
into consideration. The main objective of the study was to determine
the minimum size of ventilation opening area of the greenhouse. Five
levels of 100, 80, 60, 40 and 20% of total ventilation openings area
were tested. The experiment was carried out with a full crop (FC) and
an empty condition (EC). Temperature rise, humidity difference,
transpiration rate and air exchange rate were used to evaluate the
greenhouse performance. The results revealed that internal temperature
was increased by 1.5 ºC (FC) and 4.5 ºC (EC), respectively when the
ventilation opening was reduced to 20% of total ventilation area or a
ratio of opening to floor area of 0.2. The internal humidity was also
increased by 37.5% while the air exchange rate was reduced by 40%. The
study revealed that the ratio of ventilation opening to surface floor
area of 0.6 was the minimum requirement in order to maintain a
favourable microclimate in a tropical greenhouse.
| | Harmanto, H.J. Tantau and V. M. Salokhe
Influence of Insect Screens with Different Mesh Sizes on Ventilation
Rate and Microclimate of Greenhouses in the Humid Tropics
Agr. Engng. Intl.,2006 Vol. VIII. Manuscript BC 05 017.
ABSTRACT
An investigation on the effect of the use of nets with different
mesh-sizes on the internal microclimate and ventilation rate in
greenhouses located on the humid tropics was carried out. Three
greenhouses (each measuring 10 m wide × 20 m long) were constructed and
covered with a plastic film on the roof, and different insect proof
nets on the sidewalls, respectively. Net sizes of 40-mesh, 52-mesh and
78-mesh were used. Water vapour, transpired from 300 tomatoes
cultivated in each greenhouse, was used to determine the ventilation
rate. In addition, an energy balance method which offers a simple,
rapid and accurate way to predict ventilation rate was developed based
on common climatic data and used in this study. A good agreement (R2 =
0.85) was obtained between two methods. Statistically, the use of
insect screens with different mesh-sizes had a significant effect on
ventilation rate and internal microclimate. The reduction of
ventilation rate about 50% and 35% for the 78-mesh and 52-mesh
greenhouses, respectively was obtained compared to the 40-mesh
greenhouse. Consequently, the internal air temperature was also
increased by 1 to 3 °C. Although, a small temperature difference was
observed, the absolute humidity among treatments was significantly
different. The use of a higher mesh-size resulted in more humidity.
Ventilation rate and temperature rise in the greenhouses were strongly
correlated to the net porosity. Since their correlations were good in
agreement, the simple equation derived from the experiment will be very
useful in predicting air exchange rate and temperature rise when a new
type of net is applied.
|
| U. N. Mutwiwa, H. J Tantau and V. M.
Salokhe (2006).
Response of Tomato Plants to Natural
Ventilation and Evaporative Cooling methods.
International
Symposium on Greenhouse Cooling, ISHS, Almeria, Spain, Acta
Horticulturae 719, 447-454
ABSTRACT
In the humid tropics, high temperature and relative humidity inside
greenhouses are the main factors that hinder conventional vegetable
greenhouse cultivation. The use of fan and pad cooling systems,
application of near infra red (NIR) reflecting pigments on the roof
cover and increasing the area of ventilation openings are some of the
attempts that have been made to overcome this problem. The fixing of
insect proof screens in front of the ventilation openings prevents the
entry of some insect pests into the greenhouse but at the same time,
decreases the ventilation efficiency. The use of NIR reflecting
pigments decreases air temperature but alters the spectral transmission
of the greenhouse cover. In this research, the effects of spectral
modification (using NIR reflecting pigments), natural and forced
ventilation (evaporative cooling) on the growth of tomato plants,
Lycopersicon esculentum (Miller) `FMTT260´, were investigated by online
measurement of plant responses (phytomonitoring), in greenhouses
located at the Asian Institute of Technology, Bangkok, Thailand.
Results show clear differences in the way plants responded to different
greenhouse microclimates. In the warm season, the NIR reflecting
pigment significantly reduced the air temperature, leaf transpiration
and the net photosynthesis inside the greenhouse, but the differences
were small in the cool season. The fan and pad cooling system reduced
both transpiration and temperature (air and leaf) but had minimal
effect on net photosynthesis in the cool season. Fairly good
correlations were obtained between the net photosynthesis and the
intensity of global radiation inside the greenhouses.
| | Soni, P., Salokhe, V.M., and H.J. Tantau
(2005).
Effect of Screen Porosity on Selected Microclimatic
Parameters of Naturally Ventilated Tropical Greenhouses
Manuscript BC 05 002. Vol. VII. April, 2005. Agricultural Engineering
International, CIGR Journal of Scientific Research and Development. Available
online
ABSTRACT
Investigations were carried out in greenhouses cladded with insect
screens and natural ventilation in tropics, to quantify the phenomenon
of air-mass adherence to screen-enclosure. Four greenhouses 3 m x 6 m x
3.2 m (W:L:H) with 53, 34, 33 and 19% porosity insect screens were used
with two plant maturity stages and two plant density levels. The
shorter plants occupied 5% of gutter height while the taller stood at
50%. Plant density was doubled from 1.7 plant/m2 to 3.3 plants/m2 with
three and five rows kept parallel lengthwise respectively. Air
temperature was recorded in close proximity of cladding and
observations were made to determine the influence of screen porosity on
soil temperature, evapotranspiration and leaf temperature representing
external and internal microclimate. A heat envelope was observed up to
15 cm distance from the outside screen. A concept of heat envelope has
been proposed and discussed in terms of air temperature gradient, to
explain how wide and strong the field of influence around the insect
screens, offering resistance to mass and momentum transport. Inward and
outward temperature gradients were higher with less porous screens
(-0.88 0C and +5.7 0C) compared to porous screens (-0.44 0C and +3 0C).
Similarly, higher plant density claimed larger outward gradients (4 0C)
than single plant density (2.6 0C). Soil temperature was recorded for 5
and 10 cm depths in greenhouse pots. Porous screens evidenced maximum
downward and upward soil temperature gradients (-2.2 0C and +3.8 0C),
while less porous screens showed smaller values (-0.63 0C and +2.1 0C).
Plant evapotranspiration with matured plants inside was found to
decrease from 2,593 ml/day/plant for porous greenhouse to 2,053
ml/day/plant in less porous greenhouse.
| | Salokhe, V.M., Soni, P., and H.J. Tantau
(2005).
Effect of Net Size on Horizontal Temperature
Gradients in Naturally-Ventilated Tropical Greenhouses
Journal of Food, Agriculture & Environment (JFAE),
3(2):316-322.
Available online
ABSTRACT
Experiments were conducted in four greenhouses of sizes 3 x 6 x 3.2 m
(W:L:H) with tomato crop inside, to study the spatial distribution of
air-temperature under naturally ventilated condition. HDPE insect-nets
of 32, 40, 50, and 78 mesh having 53, 34, 33, and 19% porosity,
respectively, were used for greenhouses-cladding. Both, absolute and
relative stress-gradients of temperature were observed along the
central horizontal (x and y) axes of 3 m x 6 m greenhouse structure
with x as semi-minor and y as semi-major axes. A real-time comparison
was made among greenhouses for young and matured plants and two plant
densities single and double. Younger plants occupied 5% of gutter
height while matured statured 50%; plant density was doubled from
average 1.7 plant/m2 to 3.3 plants/m2 with three and five rows kept
lengthwise, respectively. Horizontal (x) locations exhibited 12%
temperature gradients that were found insensitive to vegetation but
lowering net porosity increased these gradients from 8% to 12%. There
was 10% temperature gradient recorded in horizontal (y) locations,
which decreased with decreasing vegetation, especially with plant
height. It was further noted that horizontal air-temperature gradients
responded considerably slower towards plant density; rather they found
to be more sensitive against plant height. Plant density, on the other
hand, altered their peak absolute values. Doubling plant density
reported significantly higher horizontal temperature gradients.
| | Soni, P., Salokhe, V.M., and H.J. Tantau
(2005).
Effect of Screen Size on Vertical Temperature
Distribution in Naturally-Ventilated Tropical Greenhouses
Biosystems Engineering, 92(4):469-482.
ABSTRACT
Nets and screening materials are often used for greenhouses in the
tropics to exclude insects. However, these nets have a direct influence
on the microclimate inside the greenhouse. A wide range of such
cladding materials are available with different mesh sizes. Experiments
were conducted in four greenhouses with a tomato crop inside, to study
the spatial distribution of air temperature in the vertical direction
under natural ventilation. Both, absolute and relative temperature
gradients were observed along the central vertical Z axis of a 3 m by 6
m greenhouse structure. A real-time comparison was made between
greenhouses with 53, 34, 33 and 19% porosity screens for two plant
growth stages (young & mature) and two plant density levels
(single
& double). Younger plants occupied 5% of the eaves height,
while
the mature plants occupied 50%; plant density was doubled from an
average 1.7 plants/m2 to 3.3 plants/m2 with three and five rows kept
lengthwise, respectively. The highest temperature value was obtained at
the points nearer to the roof, which was about 5°C higher than the
coolest point in the vertical direction. The lower 60% of the height
profile registered only 86-92% of the maximum temperature value, while
the top 40% registered 92-100%. The observed air temperature gradients
were up to 14% higher with vegetation. A decrease in porosity increased
the vertical gradients from 5% to 10%. These vertical temperature
gradient patterns were found to vary with both vegetative condition
inside and with the insect screen used to clad the greenhouse, and the
data can be used in the development of more accurate mathematical
models of air-exchange through natural ventilation.
| | Salokhe, V.M., Soni, P., and H.J. Tantau
(2005).
Spatial Variability of Air-humidity Inside
Naturally Ventilated Tropical Greenhouse Microclimate
International Agrophysics 19(4):329-336.
Available online
ABSTRACT
Research was conducted in four net-greenhouses with tomato crop inside,
to study the spatial distribution of air-humidity under naturally
ventilated condition. Both, absolute and relative stress-gradients of
air-humidity were observed for vertical (z) and horizontal (x and y)
directions with x as semi-minor axis of 3 m x 6 m greenhouse structure.
Four greenhouses with 53, 34, 33 and 19% porosity HDPE nets were used
with two plant maturity stages and two plant density levels. Shorter
plants occupied 5% of gutter height while taller statured 50%; plant
density doubled from 1.7 plant/m2 to 3.3 plants/m2 with three and five
rows kept parallel to y axis respectively. It was observed that
specific humidity gradients in vertical (z) direction increased by 30%
with vegetation. Lowering porosity increased vertical humidity
gradient. Horizontal (x) locations exhibited 25% humidity gradients
that increased with vegetation. However it decreased with less porous
nets. About 30% horizontal (y) humidity gradient was noted, which
decreased with vegetation but, lowering porosity increased it from 10%
to 25%. Horizontal gradients responded considerably slow towards plant
density, rather they found to be more sensitive to plant height. Plant
density on the other hand, altered their peak absolute values. With
matured plants inside, less porous greenhouses evidenced lesser
evapotranspiration values.
|
| V.M. Salokhe and P. Soni (2005).
Microclimatic Response of Naturally Ventilated Tropical Net-houses to
Cladding Properties
Invited Paper. In: Book of Abstracts, International Conference on
Plasticulture and Precision Farming (ICPPF- 2005), November 17-21,
2005, New Delhi, India, pp. 5.
ABSTRACT
In order to reduce the chemical uses to limit environmental hazards,
efforts are being made to exclude insects by using insect-proof
screens, especially under tropics. Tropical climates are characterized
with high summer temperature and air-humidity, where proper
air-exchange is an essential requirement with insect exclusion. Nets
and screening materials, often used in tropical agriculture to obstruct
the insect intrusion, are getting increased attention of both growers
and researchers. A wide range of such claddings are available with
different mesh-openings. Experiments were conducted to investigate the
influence of such screens’ porosity on both mass and momentum transfer
across it. Spatial distribution of air temperature and humidity
gradients in horizontal and vertical directions were measured in 3 m x
6 m x 3.2 m (W:L:H) net-houses. A real-time comparison was made among
53, 34, 33 and 19% porosity screens for two plant maturity stages and
two plant density levels.
|
| U. Mutwiwa and H. J. Tantau (2005).
Suitability of a UV Lamp for Trapping the Greenhouse Whitefly Trialeurodes
vaporariorum Westwood (Hom: Aleyrodidae).
Agricultural Engineering International: the CIGR Ejournal. Manuscript
BC 05 004. Vol VII.
ABSTRACT
Due to the increase in the demand for chemical free products and
increasing pest resistance to chemicals, there is an urgent need to
develop chemical free crop protection methods. Research was carried out
to investigate the suitability of using a special UV lamp to trap the
greenhouse whitefly Trialeurodes vaporariorum
Westwood (Hom.: Aleyrodidae) in greenhouses located in the northern
part of Germany. Four small tunnels were arranged in a cross-like
pattern, with a black compartment in the centre. In the first
experiment, the UV lamp was placed on one end above the tunnels such
that the tunnels received different light intensities. For the second
set of experiments, the UV lamp was positioned directly above the
tunnels thereby generating equal UV intensities in all the tunnels.
During each experiment, adult greenhouse whiteflies were released from
the black compartment and allowed to fly into a tunnel of their choice,
where they were recaptured using yellow sticky traps. Results show that
significantly more whiteflies were recorded on yellow sticky traps
inside the tunnels with more UV intensity. When the tunnels were
illuminated with equal UV intensities, there was no significant
difference in the number of whiteflies recorded in the tunnels. These
results suggest that it is possible to develop a special lamp for
trapping whiteflies in greenhouses.
| | Harmanto, V.M. Salokhe, M.S. Babel, H.J.
Tantau (2005).
Water requirement of drip irrigated tomatoes
grown in greenhouse in tropical environment
Agricultural Water Management, 2005, Vol. 71, 225-242
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 recommended that the cleaning of irrigation
equipments (pipe and emitter) should be done at least once during the
entire cultivation period.
|
| U. Dhakal, V. Salokhe, H.Tantau and J. Max
(2005).
Development of a Greenhouse Nutrient Recycling
System for Tomato Production in Humid Tropics. Agricultural Engineering
Agr. Engng. Intl., 2005, Vol. VII. Manuscript BC 05 008P.
ABSTRACT
Generally it is not customary to have a nutrient recycling system for
the tropical poly-net greenhouses. The main reason is the cost
involved. However, due to recent growing environmental concerns,
efforts were made in this study to develop a simple but effective
nutrient recycling system.
Tomato (Lycopersicon
esculentum Mill., var. FMTT-260)
plants were grown under two identical poly-net greenhouses. One
greenhouse was equipped with nutrient recycling system while other
without nutrient recycling as a control. The amount of water and
nutrient saved were assessed, and plant growth performance in both
greenhouses was compared.
Studies revealed that recirculation of nutrient solution could save
31.5% of total irrigation water. Among the measured major plant
essential elements, the potential saving of nitrogen, phosphorus,
potassium and calcium were 29.87%, 31.44%, 29.83% and 28.16%
respectively. The break-even of the additional cost of nutrient
recycling was less than five crop productions over a given area. The
total crop yield of the closed fertigated greenhouse was almost similar
to that of open fertigated greenhouse. Plant growth parameters (plant
height, stem diameter and leaf area index), average size and weight of
fruits, and fruit qualities (marketable fruits, moisture content, brix,
pH and firmness) of closed fertigated greenhouse were also almost
similar to that of open fertigated greenhouse. Due to recycling, the
water productivity was increased by 45.7%.
| | URBANUS N. MUTWIWA, CHRISTIAN
BORGEMEISTER, BURKHARD VON ELSNER AND HANS-JUERGEN TANTAU (2005).
Effects of UV-Absorbing Plastic Films on Greenhouse Whitefly
(Homoptera: Aleyrodidae)
Journal of Economic Entomology,
2005, 98(4): 1221-1228.
ABSTRACT
Studies were conducted to investigate the effects of ultraviolet
(UV)-absorbing plastic films on the orientation and distribution
behavior of the greenhouse whitefly, Trialeurodes
vaporariorum (Westwood).
In field experiments, small tunnels were constructed and covered with
either an UV-transmitting (Thermilux) or UV-absorbing (K-Rose) plastic
film. Results show that significantly more whiteflies were recorded in
the tunnels with high compared with those with low UV intensities.
Moreover, whitefly penetration and dispersion were less inside the
UV-deficient tunnels. These results suggest that the type of plastic
film used for greenhouse covers may have a significant influence on
both the initial immigration and distribution of T.
vaporariorum
into greenhouses. The possibilities of using UV-absorbing plastic films
for whitefly integrated pest management in greenhouses are discussed.
| | P. Soni and V.M. Salokhe (2004).
Greenhouse Automation and Its Viability under Tropical Conditions
Proceedings of Joint Conference of the 4th International Conference of
the Asian Federation of Information Technology in Agriculture (AFITA)
and the 2nd World Congress of Computers in Agriculture and Natural
Resources (WCCA), August 9-12, 2004, Bangkok, THAILAND.
Available online
ABSTRACT
The paper highlights the technological advancement and automation into
greenhouse farming worldwide, and its viability under tropical
conditions. Review revealed that in the greenhouse farming automatic
control of microclimate including temperature, humidity, delta-
duration-frequency of irrigation, fertigation, opening and closure of
vents, etc. has been achieved with precise controls and reduced human
intervention. Real time measurements and records of climatic,
agronomic/physiologic and growing-media changes enabled the grower for
executing quicker and effective measures hence act as greenhouse
decision support system. In the tropical region, dominated by
developing/under-developed countries- greenhouse automation has been
found in its growing phase. It was concluded that due to abundance of
human labor, lower market prices, higher costs of automation, lower
risk bearing capacity, lack of proper insurance/guarantee structure
against possible crop damages or price-collapse, lacking technical
know-how, smaller extent of greenhouse farms, etc. questions intense
automation; though primary or semi-automation seem to have brighter
opportunities in the protected cultivation under tropics.
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