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Trabalho
comparativo de manejo de irrigação entre Tensiômetro e
IRRIGAS
Irrigas
- a new simple soil moisture sensor for irrigation scheduling
Irrigas
- ein neuer einfacher Bodenfeuchtesensor zur Bewässerungssteuerung
P.-J.
Paschold and A. Mohammed
Stichworte
Bewässerungssteuerung, Irrigas, Tensiometer, Bewässerungszeit
und -häufigkeit, Tomate
Keywords:
Irrigation scheduling, Irrigas , tensiometer, irrigation
time, irrigation frequency, tomato
Zusammenfassung
Es
gibt zahlreiche unterschiedliche Methoden zur Bewässerungssteuerung,
aber oft sind sie kompliziert und teuer. Der neue brasilianische
Bodenfeuchtesensor, Irrigas , wurde hinsichtlich seiner
Eignung zur Bewässerungssteuerung in Geisenheim geprüft.
Basierend auf den Ergebnissen von zwei Versuchsserien
ist das neue Bewässerungssteuerungssystem als einfach,
preiswert und effektiv zu beschreiben. Irrigas initiiert
den Bewässerungsstart im Bereich zwischen -200 und -300
hPa, wenn vergleichend mit dem Tensiometer gemessen wird.
Irrigas
stellt eine einfache Methode dar, um den Beregnungstag
zu bestimmen. Wenn der Preis relativ niedrig sein wird,
kann Irrigas ein vielversprechendes Gerät zur Bewässerungssteuerung
auch in Entwicklungsländern sein, da das System auch einfach
zu handhaben ist.
In
einem Versuch erreichten die Tomatenpflanzen, deren Bewässerung
mit Tensiometer oder Irrigas gesteuert wurden, eine vergleichbare
Höhe und Anzahl der Blätter, Blüten und Früchte.
Abstract
There are many different methods of irrigation scheduling,
but often they are difficult and expensive. The new soil
moisture sensor Irrigas developed at Embrapa Vegetables
national research center(Brazil) as an irrigation controlling
system has been put into efficiency test in Geisenheim.
Based on the results obtained from two preliminary observations
the new irrigation controlling system is considered as
simple, cheap and effective. Irrigas indicated the need
for starting irrigation between -200 and -300hPa, measured
by tensiometer.
Irrigas
is an easy method of determining the irrigation day, even
for farmers who do not read and write. If the price will
be relatively cheap, the device can be a promising irrigation-scheduling
tool for poor and illiterate farmers. For commercial purpose,
where crop plants at different stages of development require
different amount and frequency of irrigation, the question
of an apparatus with automatic and semi-automatic manoeuvrings
is worth considering.
Tomato
plants, which were grown on plots under irrigation scheduled
with Tensiometer or Irrigas, had similar height, leaf,
flower and fruit number.
1.
Introduction
On global basis, water stress is a major cause limiting
productivity of Agricultural systems and food production
(BOYER, 1982). Water resources are becoming very limited
and the search for efficient water use is a major challenge
in the agricultural production system. This necessitates
the use effective irrigation controlling equipment. It
is a petty that only about 15.7% of the total cultivable
land in sub-Saharan Africa is irrigated (FAO, 1997). Among
the many reasons for the under utilisation of the water
resources, technological constraint is rated as the major
problem. Often irrigation facilities developed in the
developed world are expensive and beyond the scope of
the poor illiterate farmers.
Irrigation
control is meant to determine when, how often and how
much water to provide for the crop plants (PASCHOLD, 2002).
It is also important to note that the amount of water
supply to the crop plants depends on soil (type and field
capacity), the level of under ground water table, climate
and growth stage of the plant and the deep of its root
system.
There
are many different methods to determine the frequency
and amount of irrigation for crop plants. Often are used
Gypsum Block, Kombi sensor (DLO Wageningen), Flori (Netafim),
Watermark, Tensiometer, TDR-sensor (TOPP and DAVIS, 1985;
PASCHOLD and WIETHALER, 2000) and now for the first time
the Irrigas method. Each of these methods has their relative
advantages and disadvantages, which is beyond the scope
of this paper here to discuss. Small growers of vegetables
and fruits in Africa and other developing countries require
more than ever simple to use, effective and above all
cheap instruments to regulate small scale Irrigation.
Measurements
of water content of the soil and plant materials are based
upon the sensing of the various properties of the water
molecule viz. Measurement of mass, thermal properties,
electrical properties and response to radiation (Gardner,
1987). The Irrigas functions in such away that the porous
cup exchanges water with the soil and as the water tension
of the soil becomes greater than the critical value, the
pores, which were initially full of water in wet soil,
get empty and allow the air to move freely through the
cup walls (CALBO and SILVA, Personal communication 2002).
Evaluation of the soil moisture at this moment with the
device indicates the entrance of water into the barrel
indicating that the soil should be irrigated.
Prototype
Irrigas devices, which were supplied from Brazil to Geisenheim
Research Institute, were put first in preliminary observation
on non-cropped sandy soil from 26 April until 28 May.
The devices were found to react at soil moisture regime
from -200 hPa onwards. It was therefore necessary to further
verify the efficiency of Irrigas on the growth plants.
Hence, the objective of this observation was to evaluate
the efficiency of the new prototype irrigation control
apparatus.
2.
Materials and Methods
An
experiment was started on 4th of June 2002 at Geisenheim
Research Institute to evaluate Irrigas . A standard tensiometer
(Tensio-Check TC 1041, produced in Geisenheim) has been
used to determine the water tension in the soil by the
time of Irrigas reaction. Two plastic boxes filled with
clay loam soil were used for the experiment. In each box
were two grafted Tomato plants planted.
Irrigas
(Figure 1) was installed in such a way that a hole was
made in between the grafted tomato plants at a rooting
depth (30 cm). Then the porous cup was placed in the hole
and the soil returned and slightly pressed to create an
intimate contact between the porous cup and the soil.
Thrusting a stake, which was used hang the transparent
barrel upside down, completed the installation.
In
addition, two 30 cm-tensiometers were installed in each
box. After the first uniform watering to field capacity
with 6 l, box one was watered based on the reaction of
Irrigas while box two was watered as per the readings
from the tensiometer (-200 to -250hPa).
Moisture evaluation was done once in a day as per the
recommendation of the company to determine the moment
of irrigation. Reaction of the Irrigas was checked by
immersing the transparent barrel, attached to the end
of the tube, into the water container. To be consistent
in the measurement, the same depth of water was used every
day to evaluate the reaction of the Irrigas . The water
vase was filled with three litres of water and the transparent
barrel was immersed to a depth of 1.5 litres. Entrance
of water into the barrel was then inferred as a signal
for irrigation requirement.
Nitrogen
(2gN/m2) was given uniformly to both boxes on the 13th
June 2002. Data was also collected once a week on the
growth and development of the tomato plants
.
3. Results and Discussion:
" Reaction of Irrigas
The results of the experiment conducted from 4th June
to July 4th 2002 showed that Irrigas could be successfully
used in the determination of the irrigation time for crop
plants. 9 days after the first irrigation reacted the
Irrigas in such away that about 7cm of water entered into
the little barrel (Figure 2). At the same time the reading
from the tensiometers indicated between -205 and -240
hPa, a soil moisture regime, which is within the range
of horticultural crops (-100 and -300hPa). When the soil
moisture regime is beyond -300hPa, then it leads to reduced
plant growth because of the excessive energy required
by plants for water uptake (PASCHOLD, 2002). Following
the second Irrigation with 6 litres of water, it took
7 days for both, Irrigas and tensiometer, to signal again
the time of irrigation. Based on the weather condition
and the growth stage of the plants the irrigation frequency
and amount of water were differed from time to time.
"
Growth of Plants:
There was no difference observed regarding the growth
of the tomato plants, be it in height, number of leaves,
flowers and fruits. The relative growth rate of the plants
was the same under both circumstances. Tomato plants,
which were watered, based on the reaction of Irrigas were
little bit taller than the others, however, it was not
significant and that might have resulted from initial
difference in plants (Figure 3). This has been asserted
from the relative increment analysis of plant height.
All the plants had similar number of leaves, which were
also equally green in colour. It is also possible to notice
from the graph that plants irrigated with Tensiometer
control had a slight increase in flower and fruit number
(Figure 4). However, this was quite insignificant difference,
which cannot be attributed to the treatment.
From
the findings obtained so far it can be concluded that
Irrigas can be used to successfully determine the irrigation
moment. With regard to the amount of water to apply it
is dependent on the type of soil, the soil depth and the
crop type grown. Unlike the Tensiometer, which signals
the water deficit gradually, Irrigas reacts spontaneously
in a single day. This makes it impossible to know how
much water is there when the moisture deficit is less
to be detected by Irrigas , which functions between water
deficit of -200 and -300hPa.
However,
Irrigas is an easy method of determining the irrigation
time even for people who do not read and write. Provided
that the price remains relatively cheap, Irrigas can be
a promising Irrigation scheduling device for many poor
and illiterate farmers like in Africa. Although it is
too early to speculate from this small experiment, it
is worth to notice that provided that automatic and semi-automatic
types can be developed; Irrigas can also be a promising
device for many vegetable and fruit growers all over the
world. It is necessary however to further test the device
under field condition with more replications. Additional
observations are also needed to test the reaction of Irrigas
at different osmotic regimes of the soil.
"
How much water to apply:
With regard to the amount of water to be applied, there
is no direct recommendation so far known. The sensor tells
only when to water. As per the suggestions from the manufacturers,
in the lack of a moisture retention curve, the following
relations can be used:
"
Clay soil: 0,60mm of water / cm of soil depth;
"
Medium soil: 0,45mm of water / cm of soil depth;
"
Sandy soil: 0,25mm of water / cm of soil depth.
As can be inferred from the above suggestions, it is impossible
to provide different quantities of water at different
stages of crop growth. It is therefore worth considering
the possibility of refining the technology with regard
to possibilities of determining the amount of Irrigation
water required at different growth stages of a given crop.
4.
Conclusion:
Provided that the price remains cheap, Irrigas is a promising
Irrigation controlling apparatus. The simplicity of the
method to use makes it a best candidate for small farmers
who cannot read and write at all. However, the development
of automatic and semi-automatic version will be best fit
for commercial large-scale use. Possibilities to use the
apparatus to regulate irrigation of crops at different
stages of growth are also a major work to be considered
in refining the technology. Its reaction to different
concentrations of fertilisers and salts should further
be tested.
Acknowledgement:
We would like to thank the manufacturers of the Irrigas
and in particular to Adonai G. Calbo and Washington L.C.
Silva who gave us the sensors and an idea about the principles
of its operation.
References:
Boyer, 1982:Plant Productivity and Environment. Science
218:443-448.
Calbo and Silva, Personal communication 2002.
FAO,
1997: Irrigation Potential in Africa. A basin Approach,
Rome, Italy.
Gardner, W.H., 1987: Historical perspective on measurement
of soil and plant water status. In Conf. On Measurement
of Soil and plant water status. Vol. 1 July 6-10, 19887
Utah State Uni. USA. 1-6.
Paschold, P.-J.; Wiethaler, A., 2000: Eignung von Sensoren
zum Steuern der Bewässerung bei Freilandgemüse (Usability
of Sensors in scheduling Irrigation of vegetables) Zeitschrift
für Bewässerungswirtschaft, 35, 1, 51-62
Paschold, P.-J., Kleber, J., Mayer, N., 2002: Geisenheimer
Bewässerungssteuerung 2002. Geisenheim Irrigation scheduling
2002. Zeitschrift für Bewässerungswirtschaft 37, 1, 5-15.
Topp, G.C. Und Davis, J.L., 1985: Measurement of soil
water content using time domain reflectometry (TDR) Soil
Sci. Soc. Am. J. 49 (19), 269 - 287.
Address
of authors:
Prof. Dr. Peter- J. Paschold
Research Institute Geisenheim
Department Vegetable Crops
Von-Lade-Str. 1
65366 Geisenheim
Germany
Paschold@fa-gm.de
Ali
Mohammed
Jimma University
College of Agriculture
P.o.Box 307.
Jimma, Ethiopia
alimhmd@yahoo.com
Figure
1: Irrigas-sensor (left) and the system for measurement
in tomato crops
Figure
2: The reaction of Irrigas at different soil moisture
regimes
Figure 3: The height of tomato plants watered with Tensiometer
and Irrigas control
Figure 4: The total number of fruits per plant of tomatoes
irrigated with Tensiometer and Irrigas Control
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