This chapter will describe the capability of the system to help the grower adapt or adjust agro-technical activities according to the plant's response, taking into consideration the climate and irrigation conditions. The system may be beneficial to the experienced grower, who is familiar with advanced climate control technologies as well as growers who use simple technologies.
All the facts presented here are based on the close work carried out with growers and experimental stations in Israel, Holland and Canada during the past three years.
The review covers the following subjects:
1 Daily weight accumulation
2 Integration of forecasting as part of agro technical considerations
3 Analysis of the relationship between weight accumulation and environmental conditions
3.4 Electrical conductivity
1. Daily weight accumulationThe system provides fresh weight data of an individual stem including its leaves, stem and fruits. The accumulation of fresh weight is the result of development and growth processes that take place prior to the measurement. At the same time, climate and irrigation data are collected via a connection to the grower's climate computer.
The daily weight accumulation process for greenhouse tomatoes can be characterized by 5 growth periods, affected by different environmental conditions. Understanding of the environmental factors enables proper agro-technical adjustment during the day presented in Graph no. 1
Graph no. 1: division of the day into 5 periods and the main factors that affect each period.
The graph describes the daily weight accumulation process (red line) and the hourly growth at any given time (blue line).
1. First period – during the night, before sunrise (post- night temperatures)– the weight accumulation depends mainly on the temperature .
2. Second period – during sunrise, water availability in the substrate and the temperature directly affect the weight accumulation
3. Third period – during morning and midday, weight accumulation is mainly a result of the water balance that is determined by both the transpiration rate and the water uptake by the plant: Climate factors involved, such as radiation, temperature and humidity (Humidity Deficit) are the main factors that affect the rate of transpiration.
4. Fourth period – during the afternoon and evening hours, an accelerated process of water uptake occurs, where the plant absorbs a large quantity of water (Recharge ). This process is caused by water potential differences between plant’s roots and the substrate. In this case, the plant is affected mainly by the quantity of available water in the substrate and the water electrical conductivity.(Ec)
5. Fifth period – the period of previous night is affected mainly by the temperature.
2. Integration of Forecasting in Agro- technical considerationsThe management of the growth processes is also based on processes that took place during the previous day, combined primarily with the forecast of radiation and temperature.
The combination of the information received from plant growth measurements, climate data of the previous day and climate forecast for the following day enables the grower to optimize the agro-technical activities.
For example, the high level of radiation during the previous day, together with a forecast for high level radiation on the following day, will enable an increase in temperature during the night and the following day (Table no. 1).
The following example illustrates the changes a grower may make during the day as a result of the previous day's conditions. It is possible to raise the temperature if the level of radiation was high the previous day and a high level radiation is expected.
Table no. 1 – Combination of Previous Day's Measurements and Forecast.
3. Analysis of plant growth and environmental conditions is an efficient method for a grower to achieve rapid improvement in the growth ratesThe system enables rapid evaluation of the relationship between the environmental conditions and the growth process. The evaluation is based on the daily growth rate and a comparison between the growth rates on various days. The system receives all the environmental data from the grower's computer and provides growth performance data.
3.1: The parameter that primarily affects the growth rates is radiation.
Graph no. 2: The Growth Rate is Directly Proportional to the Radiation.
Radiation has a direct and an indirect impact on fresh weight accumulation.
The direct influence over the growth rates is expressed by the Photosynthesis processes, which determines the quantity of assimilates that later are transported to the various plant organs. These processes is followed by the uptake and transport water and minerals, which determine the plant’s final fresh weight and the commercial yield.
The indirect effect of radiation on fresh weight accumulation is mainly due to its effect on transpiration: Transpiration is linearly correlated to radiation.
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
The following graph (3) 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 day, "a".
Graph no. 3: Growth Rates During Days with Radiation fluctuations.
High radiation rates are sometimes accompanied by a significant drop in weight accumulation during the day (see Graph 3 b). This is related to the effect of radiation on the water balance : the water uptake rate by the plant is lower than the transpiration. Usually the plant recovers after this period but sometimes actual damage is caused to the growth process.
this phenomenon can be prevented or reduced by influencing factors that affect the water balance such as irrigation, shading or decreasing the humidity deficit by adding fog or “small size “ drops by sprinklers.
3.2 It appears that temperature is important climatic factor that can be used by growers to manage the growth processes or adjust the vegetative / generative ratio. Extensive information was collected in the present work regarding the effect of temperatures on plant growth.
Currently, a grower can receive feedback on the growth results from the temperature effect only after several days. By using the growth analysis system, one can follow temperature changes almost on line.
The following Graph (4) describes the effect of day and night temperature regimes on growth at night and in the morning. In those two cases the rise in temperature was accompanied by improvement in growth.
Graph no. 4: The Effect of Daytime and Night-time Temperatures on Growth Rates. In two cases, the growth rate was higher for high temperatures, as compared to days with lower temperatures.
3.3 Irrigation : Irrigation is definitely one of the most relevant factors influencing the growth process.
The system enables to follow very fast and accurately 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 due to expected problems such as Botrytis, etc. that must be taken into account.
Graph no. 5 describes the dependency between the substrate water content in the morning when irrigation starts, and the growth rate during the morning and late hours. Poor water availability was accompanied by a delay in growth during the day.
It seems that irrigation management still requires further study. The plant’s response to changes in the available water content has yet to be properly studied. The growth analysis system may be highly beneficial in this regard.
Graph no 5: Relationship between Water content level (blue) and Growth Rate (red ). Low water content level during morning hours is accompanied by a slowdown in the growth during the day.
3.4 Electric conductivity (EC): The effect of electric conductivity (EC) near the roots environment on the growth rate is highly significant. The fertilization formulas, water quality and the grower's strategy determine the EC level in the growth substrate. The water uptake by the plant is affected by a combination of many factors, including the EC level in the substrate. A high EC level near the roots can reduce the water uptake.
As previously mentioned,(article no 1 ) the growth period during the afternoon and evening hours is characterized by water uptake and rapid growth. The substrate water content is the only water source, since there is no irrigation during those hours. Usually there is an increase in the EC level during this period, since the plant takes up more water than minerals.
Maintaining a low EC level at this stage will contribute to the water uptake and to higher growth levels. (Graph 7).
Graph 7: EC level in the growth Substrate
This article is the 3rd publication in a special series of articles on HortiDaily this month.
Next week, on Thursday October 9, we will publish the 4th and last article in this special series. Dr. Menachim Dinar will then discuss 'Challenges of the Climate control system.'
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