M. Dinara and R. Golovaty
PASKAL Technologies Ltd. R&D Department, Ma’alot, Israel.

Abstract
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.

INTRODUCTION
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 installed.
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, 1994).

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 controlled manner.

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 greenhouse’s orientation.

CONCLUSIONS
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
specific questions.

ACKNOWLEDGEMENTS
Klapwijk, P., De Winter, M., Van Den Bosch, B., Seasun company ‒ Holland, Nature Fresh – Canada, GreenQ Improvement Centre – Holland.
Literature cited
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Berman, M.E., and DeJong, T.M. (1996). Water stress and crop load effects on fruit fresh and dry weights in peach (Prunus persica). Tree Physiol. 16 (10), 859–864 https://dx.doi.org/10.1093/treephys/16.10.859.
Chone, X., Van Leeuwen, C., Dubourdeieu, D., and Gaudillere, J.P. (2001). Stem water potential as a sensitive indicator for grapevine water status. Ann. Bot. (Lond.) 87 (4), 477–483
https://dx.doi.org/10.1006/anbo.2000.1361.
Sase, S. (2006). Air movement and climate uniformity in ventilated greenhouses. Acta Hortic. 719, 313–324
https://dx.doi.org/10.17660/ActaHortic.2006.719.35.
Solutions, H.G. (2015). www.hortimax.com.
Khemira, H., Lombard, P.B., Sugar, D., and Anita, N. (1993). Hedgerow orientation affects canopy exposure, flowering, and fruiting of ‘Anjou’ Pear Trees. HortScience 28, 984–987.
Van Leperen, W., and Madery, H. (1994). A new method to measure plant water uptake and transpiration simultaneously. J. Exp. Bot. 45 (1), 51–60 https://dx.doi.org/10.1093/jxb/45.1.51.

Paskal Systems organized two seminars at Delphy in Bleiswijk last week. Menachem Dinar and Joost van Rooij gave an explanation on the Growth Analysis System.

After a general introduction to the system and a quick tour through Delphy’s greenhouses, where Paskal’s unit is used daily in 100% LED tests among other things, Menachem got a little bit deeper into the system. Starting with the more simple material, and ending up at production forecasts and the use of assimilation lighting.

The latter mainly dealt with the effectiveness of lighting during cultivation. In many cases there is much to gain both in terms of production as energy saving. The Paskal Growth Analysis System can hereby be used to achieve maximum production with minimum energy consumption.

The first day was specifically organized for those interested in the system. The second day was especially for users of the system. It involved a group of growers who already use the Paskal system. Users could exchange experiences and get ideas, while Menachem further informed them about the system.

In greenhouse cultivation, supplemental lighting is usually mainly applied during the winter, when outside radiation and temperatures are low. During this period the climate regime is determined mainly by growers: temperatures are determined and adjusted through the heating system. Paskal Systems however, recently conducted a study on the effects of the decrease in hourly growth influenced by small temperature fluctuation in a greenhouse with supplemental lighting. The data outcome of their Growth Analysis System provided the following findings:

A: Slight decrease in temperatures accompanied with slowdown in hourly growth.

B: Significant slowdown in temperatures is followed by a strong and sharp decrease in growth.

The sharp decline in temperatures is determined by the grower to balance the vegetative and productive performance. However, this case study indicates that the sharp decrease is a result of reduction in growth rate but also in plant weight loss (hourly growth below zero); a negative side effect.

It is possible to improve temperature strategy by following the growth rate under various temperature conditions with the help of Paska’s Growth Analysis System (GAS). The plant will respond immediately and results from the GAS will be available the following day, in order to optimize the climate strategy even further.

On their 9 hectare greenhouse operation in Keyingham near Hull, British tomato grower Keyingham Salads Ltd is using a new growth comparison technology to improve yields and balance the differences between productions.

Keyingham Salads is growing in a total of 4 greenhouses. Two of the glasshouses are identical to each other in terms of size, design and installed technology. But somehow the grower at Keyingham Salads cannot seem to create the same yield output of both glasshouses. “Each and every year, one of the greenhouses is always a few kilos ahead in production.”

Last year Keyingham Salads experienced a difference of 4 kilos, which is why they installed Paskal’s Growth Analysis System. “We needed to have an extra tool to see what is going on in both greenhouses, and we thought that the GAS might be a good tool to use to see what happens, and to change the situation.”

Since February 2015, Keyingham Salads has been using the system to fine tune their growing strategies; they analyse the growth of the crop and makes small changes in the settings in order to optimize the production of the greenhouse that lags behind. So far they have experienced yield improvements.

“Since we’ve been using the system, we’ve been able to make better grounded decisions and analyze the settings at an early stage. This resulted in improved production in the glasshouse producing the least. Production went up in this house, but also in the other greenhouse that was already ahead. The production in both glasshouses went up by a few kilos, and the difference in yield decreased.”

Keyingham Salads said the system is key to this improvement.

“When we make small changes in the growing strategies, whether it is a change in temperature, humidity or irrigation, we can see the result within the next two days. You can immediately see the effect of your adjustments.”

Currently, they are still learning how to utilize the system to its full potential. Paskal’s agronomist Dr. Menachem Dinar visited the grower last week to analyze the output of the system as well.

“So much data becomes available, that it changes the approach to growing. Every day we are still learning a bit more about how to apply the outcome,” the agronomist concluded.

Continuous measuring of tomatoes plant growth rate was performed in 4 tomatoes greenhouses in Holland and Canada using the Paskal “Plant Growth analysis” system. Differences in growth rate between the east and the west sides of the row were observed in all 4 locations. Pattern, timing and period of this phenomenon varied among locations.

The study was conducted to evaluate greenhouse performance under various locations and different orientation.

The absolute differences were lower (-0.03 kg.m²/day /row) in Canada (A) and higher in Holland (D)- 0.06 kg/m²/day/row.

There seems to be a link between the pattern of the difference and orientation of greenhouses. Minor changes were observed in Canada – 2ᵒ orientation and larger fluctuations in Holland: – 110ᵒ and 65ᵒ orientation.
In some cases the pattern of these differences is not identical in the beginning and the late part of the growing season.

The present study does not provide scientific explanation to this phenomenon.
However, this phenomenon may provide an interesting opportunity to improve the yield by managing the trellising strategy. Timing and duration of lowering the trellising should be studied systematically.

Preliminary observations, conducted in 2013 aimed at improving rows performance by lowering the two sides of the rows separately. It is expected that the grower will be able to manage and adjust the trellising strategy according to the daily growth pattern and radiation.

Introduction

Light penetration to a greenhouse is a complex process, in which sun angles, greenhouse location, greenhouse orientation and type of cover, play an important role in the processes.
The sun’s angle varies throughout the year and the relationship between direct solar radiation and radiation inside greenhouse varies throughout the year.
Differences in photosynthesis were found between two sides of the rows in citrus. It was explained by the difference in photosynthesis efficiency between morning and afternoon, which can be caused by photo inhibition effect or Hysteresis.
Light interception by plants depends mainly on the plant’s Leaf Area Index (LAI): At an LAI of 3, an indeterminate crop theoretically intercepts about 90% of the incident light.
The spatial arrangement of plants in the greenhouse is important. It determines the amount of light that reaches the top of the plants and may also affect the quality of light to the lower parts of the plants.

Previous observations in Holland using the “plant growth analysis“ system, showed that growth rate between two side of the rows was different and its intensity was different throughout the year.
The common trellised technology practiced in modern cultivation in greenhouse tomatoes varied from a height of 2.5m to 3.5 m. Differences of trellising height between the two sides of the row indicate that it is possible to improve uniform performance between the rows.
This study will present differences in growth rate between sides of rows in four locations and discuss the practical aspects of improving the yield.

Materials and methods

Fresh weight of an individual stem was weighed continuously along the growing season, using weighing units developed especially for this purpose.
Data are transmitted every 20 minutes by radio to the computer and then to the server to process 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. Climate and irrigation data are collected from the grower’s climate and irrigation control system. Data are expressed as growth rate in units of fresh weight gr./stem or gr./day/m².

Monitoring and measurements were performed in 4 tomatoes greenhouses in the following locations. Latitude and Greenhouse orientation are specified in table no.1.

Table no 1.
Varieties and plant population were different in the various locations
A.Canada – Variety Torrero 3 stems /m²
B.Holland – Variety Grodena 3 stems /m²
C.Holland – Variety Capricia 3.9 stems/m²
D.Holland – Variety Capricia 3.3. stems/m²
100 weighing units were placed in each location, where 50 units were connected to the east side of the row and 50 to the west side. Data were collected throughout the growing season of 2014. In C. Holland data were collected in 2013 .

Results and discussion

Differences in growth rate were observed between the east and the west side of the rows in the 4 locations (Figure No. 1)
However, the pattern, timing and period of this phenomenon varied among the locations, resulting in differences between the locations.

The biggest difference were observed in location D (Holland 65ᵒ ), while the lowest difference was observed in A (Canada 2ᵒ)

The daily differences between the rows were calculated and expressed in kg/day/m² along the year (Figure No. 2)

The pattern of the differences between row sides varied along the year in the four locations. In addition, the absolute differences are different between the locations.
The absolute differences were lower -0.03 kg/m² in Canada (A) and higher in Holland (D)- 0.06 kg/m² . Values in Holland ( B,&C) varied between 0 to 0.3 kg/m².

There seems to be a relationship between the fluctuations phenomenon and the greenhouses orientation. Minor phenomenon changes were observed in Canada (A) 2ᵒ, orientation and larger fluctuations in Holland, mainly in (C) 110ᵒ and (D) 65ᵒ.

The differences in growth between the rows are illustrated by presenting the accumulated values of the differences between the rows throughout the growing period (Figure No. 3).

The pattern of accumulation differs between the various locations.
In Canada (A, 2ᵒ) – it seems that there are differences in the nature of the changes between the beginning of the season and the following stages.

In the Netherlands – with a slight change of orientation compared to the North (B, 15ᵒ), there are also differences between the beginning of the season and it’s following stages.

When the orientation of greenhouses is clearly different from the North (C, 110ᵒ & D 65ᵒ) the accumulation curve shows the same pattern at the beginning of the season and it’s following stages, with a break between the two parts of the season.

Table 2 shows the absolute yield of the rows, as well as the calculation of the differences between the rows.

In addition, a calculation was conducted to present differences between the rows that are greater than + 0.005 kg/m² or less than -0.005 kg/m². This calculation took into account differences in the course of the season, when one line was lower than the other on a certain date and then this row became inferior to the second row.

The above phenomenon is also expressed in Figure No. 4:

There seems to be a large difference between locations, in the range of higher than +0.005 or less than -0.005.
This phenomenon is more pronounced in locations where greenhouse orientation is significantly different than North – South ( compare D&C to A&B).

Discussion

It appears that differences in growth rates between row sides in this study are a consistent pattern of the phenomenon.

The differences between east and the west can be explained by differences in photosynthesis efficiency between morning and afternoon. This phenomenon was quoted in several crops.

However, the present study does not provide any scientific explanation to the phenomenon observed in this study: The difference and pattern between the two sides of rows in the beginning of the season and in the late stage of the season is unclear.

It is logical to assume that several factors are involved in this phenomenon, including light intensity, plant development status, plant density, varieties and more. It would be interesting to study the effect of defused light on this issue.
It was clear that greenhouse orientation is linked with this phenomenon, but more research is required to elaborate this subject.

Preliminary observations were conducted for the purpose of improving rows performance by separately lowering the two sides of the rows (Star growers 2013).
This was accompanied by improved light penetration toward the top of the opposite rows and better performance.

Since the accumulated differences between rows varied between 3 to 7 kg/m, 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 controlled manner.