M. Dinara and R. Golovaty
PASKAL Technologies Ltd. R&D Department, Ma’alot, Israel.
Paskal Technologies Ltd. has developed a Plant Growth Analysis (PGA) system
that enables the monitoring and analysis of the daily weight accumulation processes.
The system weighs individual stems in the greenhouse using a weighing unit
developed especially for this purpose. Data are transferred every 20 minutes by radio
to the computer and then to the server for data processing using software that was
developed especially for this purpose. The processed data are transferred to the
grower via the internet website on the following day. Climate and irrigation data are
collected from the grower’s climate and irrigation control systems and presented with
the growth data. Continuous weighing of the stem offers the unique advantage of
quick identification of changes in the growth rate and in the plant’s response to
environmental conditions. By understanding the processes, the grower is able to
identify and improve agro-technical activities. By placing weighing units at various
locations throughout the greenhouse, the growth rates in the various sections can be
compared and the variation in the greenhouse can be assessed. This information
reveals locations with a low growth rate (hotspots), and enables the grower to achieve
improvement during the growth season or between seasons. The system also poses
important challenges for the climate control companies. The weighing unit is actually
a new sensor that can be part of the greenhouse sensors system. The weighing process
provides fast feedback on the growth rates in real time. The monitoring indicates that
the plant responds quickly to environmental conditions; which in turn requires
changes in the control approach.
Keywords: daily growth, solar radiation, temperature, wind
Greenhouse and crop management are based mainly on grower knowledge and
experience. Long term growing strategies are determined according to the grower
expectation to yield and quality, while short term activities are determined mainly by
interpretation of plant performance. In agricultural practices, short-term response is
normally expressed in quality indicators and not in quantitative values. There is a constant
effort to develop a method for quantifying short term processes which will enable to
diagnose and change the growth pattern for improving management and control (Chone et
al., 2001). Photosynthesis measurement is probably the most relevant indicator to estimate
growth process. However, measurements are performed on individual or group of leaves and
it is difficult to evaluate the effect on the whole plant or on the whole population in the
greenhouse. In addition, photosynthesis measurements provide good estimation on dry
matter production but not on fresh yield.
Effect of climate and irrigation on growth or fresh weight accumulation is normally
expressed after a few days or longer. There is no practical method to follow plant response
as is expressed in a weight accumulation in a very short time and to change irrigation and
climate management accordingly. At present a growth measurement by hanging plants has
been developed by Hortimax growing solutions company (www.hortimax.com), the system
is very accurate but it is located in one location in the greenhouse and provides information
only on a few plants.
Plant research is practically focuses on investigating the effects of various parameters
and the interaction between them on plant performance (Bakker et al., 1995).
It will be very helpful for research and growers to have a rapid or almost online plant
response to climate and/or irrigation. This will enable the grower to tune and control
growth on a daily basis based on the actual plant growth. Most of the growers and certainly
research institutes have interest to compare between new technologies, and there is a great
importance of having results in a very short time as it will enable to adjust the growing
technologies. The presented PGA system provides an almost on line measurement of plant
fresh weight along the day and along the growing season. The number of units per area is
determined according to greenhouse’s size, the processed information is provided to the
grower’s computer by the internet.
MATERIALS AND METHODS
Fresh weight of an individual stem was weighed continuously along the growing
season. The system weighs individual stems in the greenhouse using a weighing unit which
contains load cell, battery, and radio developed especially for this purpose. The weighing
unit is hanging on the trellising system and is temperature compensated. Data are
transmitted every 20 minutes by radio to the computer and then to a server for processing
the data, using software that was developed especially for this purpose. Processed data are
transmitted to the grower via the internet website on the following day, in the very near
future data will be provided on line to the grower.
Climate and irrigation data are collected from the grower’s climate and irrigation
control system. Data are presented as fresh growth rate in units of g stem-1 or g day-1 m-2.
Monitoring and measurements were performed with 100 weighing units that were placed in
4 locations, where 50 units were placed on the east side of the row and 50 to the west side.
Cultivars and plant densities were different in the various locations, latitude and greenhouse
orientations are specified in Table 1. Data were collected throughout the growing season of
2014 in Canada (A), and Holland (B and D), Data from Holland (C) were collected in 2013.
Table 1. Countries, cultivars, plant density, latitude and orientation where the system was
Country Cultivar Stems (m-2) Latitude/orientation
A Canada Torrero 3 N 42°08’/2°
B Holland Grodena 3 N 5°20’/15°
C Holland Capricia 3.9 N 51°57’/110°
D Holland Capicia 3.3 N 52°27’/65°
RESULTS AND DISCUSSION
The present study is focused on understanding the short term fresh weight
accumulation. Daily weight accumulation process for greenhouse tomatoes can be
characterized by 5 growth periods which are affected by different environmental conditions.
Understanding of the environmental factors enables proper agro-technical adjustments
during the day (Figure 1): temperatures and water balance are the main factors that affect
weight accumulation along the day. This was observed previously (Van Leperen and Madery,
Figure 1. Main factors that influence the growth rate along the day, according to the period
of the day: 1 ‒ post night: temperatures, 2 ‒ morning: temperatures and water
availability, 3 ‒ midday: water balance and humidity deficit level, 4 ‒ afternoon:
water balance and Ec level, 5 ‒ pre night: temperatures and water availability.
The grower can quickly observe changes: a sharp decline in growth draws his
attention to a possible problem (Figure 2). Possible changes in temperature, irrigation or
other parameters will be reflected in more rapid growth rate.
Figure 2. Sharp differences in growth between days may indicate a problem.
There is an obvious link between the accumulation of fresh weight throughout the
growing season and yield accumulation (Figure 3). The ratio between fresh weight and dry
weight will be affected also by water stress and crop load (Berman and DeJong, 1996).
Actual yield presented here is the commercial yield provided by the growers, and the
accumulating fresh weight data was measured by the weighing units. Shifting yield
accumulation curve for three weeks back reflects the ratio between fresh weight
accumulation and yield accumulation. This gives the grower a possibility to predict
capabilities of yield and harvest timing.
Solar radiation is the main parameter that affects the growth. It has a direct and an
indirect impact on fresh weight accumulation. The direct influence on the growth rates is
expressed by the photosynthesis process, which determines the quantity of assimilates that
later are transported to the various plant organs. These processes are followed by the uptake
and transport of water and minerals, which determine the plant’s final fresh weight and the
commercial yield (Figure 4b).
The indirect effect of radiation on fresh weight accumulation is mainly due to its effect
on transpiration. The pool of assimilates, created by the photosynthesis processes, has an
effect on the daily growth and the effect continues on the following day’s growth. For example,
low radiation during a particular day is not necessarily accompanied by low weight accumulation on that day, if during the previous day,
the radiation was high and the pool of assimilates formed was sufficient to ensure growth on the following day.
Figure 4a illustrates
the long-term effect of radiation: the plant growth was not affected by one day of low
radiation, as the pool of assimilates created in the previous day contributes to the growth on
the following days.
Figure 3. Fresh weight accumulation (kg m-2) measured by PASKAL weighing units, and
yield (provided by the grower): (a) actual dates, (b) shifting yield accumulation
21 days back.
Figure 4. Fresh weight and radiation: (a) 7 days fresh weight growth (g day-1) and solar
radiation sum (J cm-2); (b) relationship between fresh weight accumulation (kg
m-2) and accumulated radiation (MJ m-2).
Temperature is an important climatic factor, and is used by growers to manage the
growth processes or adjust the vegetative/generative ratio. Extensive information was
collected in the present work on the effect of temperatures on plant growth. Currently, a
grower can receive feedback on the temperature effect on growth only after several days. By
using the PGA system, one can follow temperature changes almost on line.
Figure 5 describes the effect of day and night temperature regimes on growth at night and in the
morning. Increase in night temperatures is positive correlated with growth acceleration
(Figure 5b). Day temperature effect on growth is linked to radiation (Figure 5a). It was
observed that under high radiation conditions, plant responses positively to high
temperatures which are considered to be above optimum (Figure 5a). Growers will be able
to adjust ventilation considering the plant growth and radiation.
Figure 5. Day and night temperatures effect on growth: (a) day temperatures, radiation
sum and daily fresh weight; (b) night temperatures and fresh weight daily growth.
Irrigation is definitely one of the most relevant factors influencing the growth process.
The PGA system enables to follow very fast and accurately on the effect of irrigation timing,
drainage rate, and Ec level in the roots’ environment on the growth rate. The first irrigation
of the day, or night irrigation, affects the morning growth as well as the growth during the
later hours. In some cases, late morning irrigation was found to slow down growth during
the day probably as a result of law water availability. Of course growers are concerned about
irrigating too early in the morning due to expected problems such as Botrytis, etc. which
must be taken into account.
Figure 6 illustrates the capability of the system to detect fast
plant growth response to irrigation in soil culture (Figure 6a), positive effect of night
irrigation (Figure 6b) and present different irrigation strategies on performance of plant
growth in two sizes of growing bags (Figure 6c).
An interesting phenomenon observed in various places is the effect of wind direction
and intensity on the growth rate pattern of the plants. The effect of air flow on greenhouse
climate is well documented (Sase, 2006). However, it seems that the effect of wind on
greenhouse performance appears to be very significant.
Figure 7 illustrates the outside
wind’s impact on the growth rate in various compartments inside the greenhouse.
Significant differences in growth rates were observed in various compartments when the
wind direction or its intensity changed. The damage caused to the crops during those days
was expressed in a drop in the growth rate and to a decrease in uniformity within the
greenhouse. It is clear and known that plants react very quickly to air flow inside the
greenhouse, especially when the level of air humidity is low. The existing control systems
enable to regulate the opening of windows according to the wind direction and intensity.
However, these applications do not take into consideration the wind behavior and its impact
on plant growth inside the greenhouse.
Differences in growth rate were observed between the east and the west side of the
rows in 4 locations (Figure 8). This was observed also in peaches (Khemira et al., 1993).
However, the pattern, timing and period of this phenomenon vary among the locations. The
biggest difference between row sides were observed in location d (Holland N 52°27’: 65°),
while the lowest difference was observed in location a (Canada N 42°08’: 2°). Preliminary
observations were conducted for the purpose of improving rows performance by separately
lowering the plants in the two sides of the rows. This was accompanied by improved light
penetration towards the top of the opposite rows and better performance. Since the
accumulated differences between rows varied between 3 to 7 kg m-2, it can be estimated that
there is an economical potential to minimize the gap between rows by improving light
penetration to the shaded row. This can be done by separately lowering the two rows: timing
and length of lowering should be studied systematically by following on-line the daily
growth rate of the two rows. This will enable the grower to manage the process in a
Figure 6. Irrigation study: soil, night irrigation, slab size: (a) soil irrigation, water tension
(mbar) 20 cm depth, and daily growth; (b) growth and night irrigation; (c) growth
and water content in two slab sizes.
Figure 7. Wind effects on compartments’ performances. (A) Wind direction and growth in 6
compartments. (B) When the wind changes its direction there are bigger
differences between the growths in the 6 compartments. (C) Effect of windows’
opening on growth. (D) Effect of wind’s speed on growth.
Figure 8. Fresh weight production (g m-2) on opposite sides of the row along the growing
season in 4 locations: (a) Canada – cultivar ‘Torrero’ 3 stems m-2, N 42°08’/20°;
(b) Holland – cultivar ‘Grodena’ 3 stems m-2, N 52°00’/150°; (c) Holland – cultivar
‘Capricia’ 3.9 stems m-2, N 51°57’/110°; (d) Holland – cultivar ‘Capricia’ 3.3 stems
m-2, N 52°27’/65°. The differences between the locations are mainly due to the
Quick identification of changes in the fresh growth rate has important agricultural and
economic benefits. The PGA system identifies failures or changes in the growth processes
long before the grower can detect that by any other measure. As a rule, by the time the
grower can observe and diagnose the problem, the damage or the decrease in the growth
rate already exists and it is already too late to respond properly. Today, growers manage the
crops to the best of their knowledge. The new capabilities offered by this system can
significantly improve the management and control methods employed by growers. The
weighing unit is actually a new sensor that can be part of the greenhouse control system.
The weighing process provides quick feedback on the growth rates in real time. The
monitoring indicates that the plant responds quickly to environmental conditions; which in
turn required changes in the control processes. The large amount of weighing units in the
greenhouse, and the high correlation between fresh weight and yield, provide new
capabilities related to yield forecast, compare options and improving uniformity. The system
allows developing new directions in agricultural research by obtaining immediate results on
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