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AGRO-TECHNOLOGIE
Appareils de mesure
SYSTEM
PEPISTA
Made in France by AGRO-TECHNOLOGIE
DETAILED DOCUMENTATION
SYSTEM PEPISTA
Summary
- AGRONOMICAL
. The advantages of PEPISTA
1. Biological reminders
11. A plant's life
12. A plant's water requirements
13. A plot of land's irrigation requirements
2. Micrometric variations
21. Characteristic signs
22. Biological interpretation
221. Signs of well-being
222. Signs of lack of water
23. The meaning of the micrometric signal
- SCIENTIFIC AND AGRONOMICAL DOCUMENTS
- PRESS REVIEW
THE ADVANTAGES OF PEPISTA
The major advantage of PEPISTA is that it constantly gives clear information, straight from the plant, without disturbing it.
1. BIOLOGICAL REMINDERS
11. A plant's life
A plant is a living being which has an anchoring system in the ground : roots which are also an exchange zone for absorbing water and the indispensable minerals. The leaf system makes up the receptive surface of solar energy which enables a chlorophyll synthesis. However, the leaves also make up (through microscopic apertures : stoma) the zone through which carbonic gaz, the raw materiel for the making of organic molecules penetrates. These same stomas are used for transpiration and let out the quantity of water required by climatic needs. This transpiration is a capital phenomenon as it is the motor of the rising movement of the sap, of the absorption of water and nutritional elements by the roots. The greater the transpiration, the more absorption is activated.
Stomas have variable opening which is mainly controlled by light intensity, the brighter the light, the better is the photosynthesis, but also the greater is transpiration, therefore the move water is consumed by the plant.
12. A plant's water requirements
In order to function well, a plant must be able to absorb as much water through the roots as it loses through transpiration by the leaves. The water balance must be equal. Yet, as for all biological balance, it is not a mathematical balance at all times, but rather a succession of imbalances which compensate one another in time. It is just necessary that over a few days' time, the intake of water has on the whole compensated the outgoing.
All living beings have developed adaptation mechanisms. Plants, no more than animals or humans, do not need to drink each time they transpire. However, if there is a shortage over too long a time, men and animals become thirsty, that is their nervous system translates the exaggerated disturbance of certain physiological parameters as an urgent order to drink.
This is the exact role of the PEPISTA system detecting on the plant any disturbance of the parameters sensitive to a lack of water and ordering : irrigation in time.
13. Irrigation requirements of a plot of land
Crops need water and this water must be regularly available. That is why, in many areas where there is insufficient or irregular rainfall, it is necessary to bring in water in an artificial way : that is irrigation. Water is the first limiting factor ; in other words if there is not enough water, it is impossible to grow crops.
To irrigate is to bring water to a plot of land : that is to say, to a certain surface area with its type of soil, its topography a certain type of crop, its micro-climate and a certain number of technical constraints. a plot of land is not only a plant area, but also all the other elements that are a part of its functioning with the farming techniques.
Irrigating is a technical operation which brings water to a piece of land so that productivity is most satisfactory.
We irrigate according to the requirements of a plot of land. A plant's water requirements only represent a part of the quantity of water needed by the crop because this quantity also depends on the way it is brought in.
2. MICROMETRIC VARIATIONS
21. Characteristic signs
Figure 1 corresponds to display on the screen (standard software programme) of the evolution of a branch of an apple tree over 7 very sunny days in may.
Screen display
Only the variations in diameter with regard to the original point are interesting but the position of this point is of no importance. In fact, its position is automatically directed by the software programme so that the lowest diameter is at 0 (during the period observed).
In the top left-hand corner of the graph is a figure indicating the scale of diameter variations. A value 50 of figure 1 means that there are variations between 0 and 50 points (0 to 0.5 mm), the "point" being the smallest variation possible (0.01 mm). To make it easier to read, the full scale (here 50 points) is separated into 10 horizontal strips ( here, 1 strip = 5 points = 50 micrometers = 5 hundredths of a millimeter).
Vertical dotted lines separate successive days at 0 hour for each day, three markers indicate : 6,12 and 18 hours (here, sun hours). The date (day) is written under each day.
The figure on the far right of the curve (2) indicates the number of the way displayed.
Analysis of figure 1
The general tendency over the week is rising, but with characteristic undulations owing to a lessening of the diameter (contraction) during each day.
The curve which links the maximum figures shows the daily evolution (over 24 h). In the PEPISTA system "daily growth" (24 hour diameter variation from midnight to midnight) gives the daily component (slope) of long-term evolution, the sign and intensity of which reveal the state of the plant.
22. Biological interpretation
At sunrise, light causes the stoma to open. These are closed during the night ; the plant starts to transpire and if the day is light, this transpiration will increase until the afternoon. During this first phase the plant transpires more than it can absorb through its roots, even in very damp soil.
This shortage in the water balance is only possible if certain plant tissues lose water, which reduces their volume : the diameter of the organs concerned therefore is reduced too.
Day contraction amplitude (ACD) or loss of diameter between the morning maximum and the afternoon minimum is linked to the intensity of the participation of the water reserves of the part which is measured.
As soon as transpiration stops increasing, the plant reconstitutes its reserves, on condition that there is water available in the soil ; the plant "swells up again", its diameter increases : in growing organs the cells will be able to grow. From the afternoon minimum to the maximum on the following Morning, diameter increase corresponds to water recuperation plus growth.
As long as recuperation takes place correctly, at the end of the day, contraction is a normal phenomenon which accompanies plant transpiration and indicates that it is functioning well. Even with correct water availability in the soil, the contraction increases according to climatic needs.
221. Signs of well-being
This adaptations enables the plant to make the most of solar energy at the price of a slight temporary dehydration. Everything goes very well as long as the soil is sufficiently damp for it to supply the essential part of day transpiration and to enable reserves to be recuperated when there is low water demand (in cloudy weather, late afternoon, at night time).
When a plant is in the best functioning conditions and specially when there is constant fine weather and water available in the soil, the micrometric data have special characteristics.
On the branch or stem (fig. 1)
Long term evolution is stable with a rising slope. Figure 1 shows daily net growth between 2 and 3 points.
When there is stable weather over successive days, the climatic demand and day contraction amplitude (ACD) remain quite stable. In figure 1, the ACD which is at most 25 points, is only at 16 points on the 11th, when cloudy intervals in the middle of the day enabled the plant to recuperate.
On the fruit (fig. 2)
The growth of fruit is always more spectacular and greater than the stems. It can be between 100 and 10 points on day, depending on the species and the time. On the other hand, the ACD is often less and sometimes inexistent (apples after the end of june).
Figure 2 shows the evolution of a kiwi fruit with daily growth about 30 points/day and contractions at around 10 points.
222. Water shortage signs
When ground water is rare and difficult to extract plants have to draw on their reserves more.
Day contraction amplitude increases, recuperation takes place with difficulty. Daily growth slows down, becomes nil because it is transformed into daily decrease in growth.
All these phenomena are characteristic of thirst. They announce that the plant sets off its mechanism for adapting to and surviving through drought.
The main reaction is the stomatic regulation phenomenon : in the middle of the day, the plant will reduce the opening of its stomas to reduce its transpiration, which causes a drop in photosynthetic activity.
Good irrigation means supplying water to the plant before it is obliged to reduce its activity due to a shortage of water.
Shortage of water on a tomato stem (fig. 3)
The crisis starts off on 3rd, worsens on 4th when ACD reaches 50 points, irrigation on 5th allows recuperation and a return to more normal working. In this case, the situation is not excellent because this tomato, which has just been transplanted has not recuperated its daily growth.
Shortage of water on a peach branch (fig. 4)
On 12th and 13th the situation is normal with just a lower climatic demand on 13th. On 14th, the roots of this experimental peach tree were taken out of nutritional solution in which they were soaking. Cut off from all possibilities of absorbing water, the peach tree drains its reserves in 5 days without any possibility of feeding.. In the ground this figure cannot be obtained because ground water reserves are drained less quickly.
Shortage of water on an apple tree, branch and apple (fig.5)
For the first two days the branch loses 10 points whereas the apple (way 5) only grows by 10 points. Irrigation on the 3rd restarts growth of the branch, the apple gains 15 points that day, then 23 points on the 4th, it will reach 35 points the next day, which is the normal "cruising speed" for a "Golden" 5 days before harvesting.
It should be noted that the apple shows no contraction but on the other hand it "swells up" during hot periods. It is the effect of thermal dilatation of the apple which warms up whilst its tissues can no longer give up water (held back by the accumulating sugars)
Shortage of water on corn (fig. 6)
This figure shows a special presentation it is not trace with variations accumulated over the whole week, but with a retiming at midnight on a same base line (marked by the arrow). The comparison of successive days is easier like this, the presentation is exceptional and not accessible with the standard software programme.
The setting in of water shortage is very visible over the first 3 days diameter loss of 4 to 5 points/day, ACD increasing. Irrigation on 20th allows recuperation, then regular functioning with ACD of no more than 4 points.
23. The meaning of the micrometric signal
Micrometric measurement enables objective data to be obtained directly from the plant about how it is adapting to climatic conditions and about the real availability of water in the soil.
Micrometric measurement therefore integrates all the functioning of the plant as far as its water balance is concerned. However, it only relates the water which is accessible to the roots (which is the most important for the plant), without necessarily being able to explain what is really happening in the ground.
P E P I S T A
Translation of plant behaviour by analysis of diameter variations in the plant and its application to the automatization of irrigation piloting.
PELLOUX G., LORENDEAU JY., HUGUET JG., I.N.R.A. Avignon, France
INTRODUCTION
The measurement of diameter variations on fruits or branches can yield information about the hydrous state of the plant (ZOZLOWSKI 1968, HUGUET 1985, LI & HUGUET 1989). On this principle the National Institute of Agronomical Research in France (INRA) has filed an application for a patent concerning an "Irrigation bioprogramme or PEPISTA system".
The aim of this device is to adjust water input as close as possible to the plants' needs, through interpreting diameter variations of fruit and branches.
RESULTS
In a test carried out in the middle Rhône valley (France), a region where there is a severe lack of water during most of the growing season, PEPISTA has cleary improved water feeding efficiency and crop quality (positive effect on fruit quality (chart 1).
CONCLUSION AND PERSPECTIVES
Micrometrics is the right method for observing all modification in a plant's water condition through stem contraction and the growth of stalks and fruits.
The PEPISTA system therefore appears to be a multi-purpose method for guiding irrigation on varied crops, which has the great advantage of being capable of adapting as closely as possible to a plant's real needs.
In the longer term, the research work undertaken at INRA from the PEPISTA procedure will enable its interpretation to be linked to our biological experience (growth model, effects of water availability on the quality of the fruits, lack of fertiliser symptoms ...) The coming version of TAMARIS programm will therefore be able to bring greater help to crop growing.
BIBLIOGRAPHY :
HUGUET J.G. 1985 Appreciation of the hydrous state of a plant through consultation of the micrometric variations of the size of fruit or stems during the day. Agro. : 733-741 KOZLOWSKI T.T. 1968 Diurnal charges in diameters of fruits and tree stems of Montmorency cherry. J. HORT. SCi. 43: 1-15 LI S-H, HUGUET J.G. 1989 Irrigation scheduling in a mature peach orchard using tensiometers and dendrometers.
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