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.

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°

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.

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.

Klapwijk, P., De Winter, M., Van Den Bosch, B., Seasun company ‒ Holland, Nature Fresh – Canada, GreenQ Improvement Centre – Holland.
Literature cited
Bakker, J.C., Bot, G.P.A., Challa, H., and Van de Braak, N.J. (1995). Greenhouse Climate Control- An Integrated Approach (Wageningen, The Netherlands: Wageningen press), pp.279.
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
Sase, S. (2006). Air movement and climate uniformity in ventilated greenhouses. Acta Hortic. 719, 313–324
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.