Abstract:
Most of the water used by man goes to irrigation. A major part of this water is used to irrigate small
plots where it is not feasible to implement full-scale Evapotranspiration based irrigation controllers. During the
growth season crop water needs do not remain constant and varies depending on the canopy, growth stage and
climate conditions such as temperature, wind, relative humidity and solar radiation. Thus, it is necessary to find
an economic irrigation controller that can adapt the daily water application to the plant needs. The dramatic
development of Programmable Logic Controllers, PLCs, and their rather affordable price has made it possible to
use them as stand-alone irrigation controllers. In this paper a PLC is used to adapt the daily irrigation amount to
actual ETc, using a Hargreaves-Samani type equation. This equation only requires temperature values to
calculate Evapotranspiration. Once the ETc is calculated, then the PLC manages the irrigation according to the
characteristics of the field, the irrigation equipment and the growth stage of the crop. First year results are very
encouraging and indicate a 12% saving in irrigation water. It was also found that heat flux form the soil can
influence canopy temperature.
Introduction
Water is becoming a precious resource.
Municipalities use thousands of cubic meters of
purified water to maintain the parks and green areas
in cities and towns. They rely on controllers with a
fixed schedule to operate the irrigation systems.
These controllers are usually programmed to satisfy
the peak water need, and end up wasting a lot of
water on cooler or clouded days. Farmers with drip
and sprinkler systems also use fixed schedule
irrigation programmers and thus end up wasting large
amounts of water in cooler days and at the beginning
of the growing season when the crop water needs are
minimum.
The purpose of this work is to develop
autonomous irrigation systems that use a single
climate criterion to adapt daily irrigation depths to
plant needs. Criteria such as temperature.
Present day irrigation controllers
Water is gradually becoming one of the most
precious natural resources. Meeting future water
needs requires aggressive conservation measures.
This requires irrigation systems that apply water to
the landscape based on the actual water requirements
of the plants. Many types of irrigation controllers
have been developed for automatically controlling
application of water to landscapes. Known irrigation
controllers range from simple programmers that
control application depth based upon fixed schedules,
to sophisticated devices that vary the watering depth
according to climatic data obtained from expensive
weather stations.
Material and Methodology
The PLC and controller
Various industrial PLCs were studied, including the
Siemens MicroMaster, Ibercomp uPLC IV and the
Bipom MM-51. After careful consideration the
Industrologic IC51 controller was selected due to its
particular characteristics, including the fact that it has
8 output relays, allowing it to simultaneously control
eight independent irrigations sectors. It is based on a
Atmel AT89C51 processor and can be configured
with up to eight 12 bit A/D inputs which are essential
for reading air temperature values (Fig.2). Its low
cost and modularity (possibility of being used with or
without a touchpad and a LCD) was also taken into
consideration, as a plus factor.
The programming language used by the
Industrologic PLCs is Tiny Machine Basic written
specifically for the hardware on the IC51. Given the
limited memory of the controller, (8K EEPROM)
Tiny Machine Basic was used as the only valid
programming tool. This is better than the LOGO!soft
software used by Siemens, although not as dynamic
and capable as the Bascom Basic used by the other
PLCs.
Irrigation Program
The PLC was programmed to carry out hourly
temperature readings, and at the end of every 24h
period, calculate the average, maximum and
minimum temperatures. With this information it
calculates the ETo using the Hargreaves-Samani
equation. The main challenge of working with the
IC51 is that it uses only 8bit numbers, thus larger
numbers had to be avoided. Also Tiny Machine Basic
does not have many mathematical functions, so, for
example, the square root function had to be carried
out resorting to a square root table nested in the
program. The program flow chart is presented in
Table 2.
Conclusion
In this work an adaptive irrigation controller was
developed and tested in a 2000m2 corn field. A rather
inexpensive PLC was used as the heart of the system
making hourly measurements of air temperature at a
height of 1.5m. These temperatures were registered
and used by the PLC to calculate daily reference
Evapotranspiration from a corn-field. These values
were then converted to ETc, using the methodology
and Kc values originally proposed by FAO56.
The program then used this information to
calculate the exact depth of water needed daily by the
crop to ensure maximum production. The irrigations
were carried out using a drip system, with drippers
spaced at 0.2m and a flow rate of 1ls-1.
The first year results were satisfactory indicating a
12% water saving, along with some increase in crop
yield, when compared to irrigation with a fixed water
depth using a standard irrigation controller.
It was observed that in the particular case of corn,
the use of Crop Coefficient values is very important,
as it leads to significant water saving at the beginning
and end of the growth season.
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Most of the water used by man goes to irrigation. A major part of this water is used to irrigate small
plots where it is not feasible to implement full-scale Evapotranspiration based irrigation controllers. During the
growth season crop water needs do not remain constant and varies depending on the canopy, growth stage and
climate conditions such as temperature, wind, relative humidity and solar radiation. Thus, it is necessary to find
an economic irrigation controller that can adapt the daily water application to the plant needs. The dramatic
development of Programmable Logic Controllers, PLCs, and their rather affordable price has made it possible to
use them as stand-alone irrigation controllers. In this paper a PLC is used to adapt the daily irrigation amount to
actual ETc, using a Hargreaves-Samani type equation. This equation only requires temperature values to
calculate Evapotranspiration. Once the ETc is calculated, then the PLC manages the irrigation according to the
characteristics of the field, the irrigation equipment and the growth stage of the crop. First year results are very
encouraging and indicate a 12% saving in irrigation water. It was also found that heat flux form the soil can
influence canopy temperature.
Introduction
Water is becoming a precious resource.
Municipalities use thousands of cubic meters of
purified water to maintain the parks and green areas
in cities and towns. They rely on controllers with a
fixed schedule to operate the irrigation systems.
These controllers are usually programmed to satisfy
the peak water need, and end up wasting a lot of
water on cooler or clouded days. Farmers with drip
and sprinkler systems also use fixed schedule
irrigation programmers and thus end up wasting large
amounts of water in cooler days and at the beginning
of the growing season when the crop water needs are
minimum.
The purpose of this work is to develop
autonomous irrigation systems that use a single
climate criterion to adapt daily irrigation depths to
plant needs. Criteria such as temperature.
Present day irrigation controllers
Water is gradually becoming one of the most
precious natural resources. Meeting future water
needs requires aggressive conservation measures.
This requires irrigation systems that apply water to
the landscape based on the actual water requirements
of the plants. Many types of irrigation controllers
have been developed for automatically controlling
application of water to landscapes. Known irrigation
controllers range from simple programmers that
control application depth based upon fixed schedules,
to sophisticated devices that vary the watering depth
according to climatic data obtained from expensive
weather stations.
Material and Methodology
The PLC and controller
Various industrial PLCs were studied, including the
Siemens MicroMaster, Ibercomp uPLC IV and the
Bipom MM-51. After careful consideration the
Industrologic IC51 controller was selected due to its
particular characteristics, including the fact that it has
8 output relays, allowing it to simultaneously control
eight independent irrigations sectors. It is based on a
Atmel AT89C51 processor and can be configured
with up to eight 12 bit A/D inputs which are essential
for reading air temperature values (Fig.2). Its low
cost and modularity (possibility of being used with or
without a touchpad and a LCD) was also taken into
consideration, as a plus factor.
The programming language used by the
Industrologic PLCs is Tiny Machine Basic written
specifically for the hardware on the IC51. Given the
limited memory of the controller, (8K EEPROM)
Tiny Machine Basic was used as the only valid
programming tool. This is better than the LOGO!soft
software used by Siemens, although not as dynamic
and capable as the Bascom Basic used by the other
PLCs.
Irrigation Program
The PLC was programmed to carry out hourly
temperature readings, and at the end of every 24h
period, calculate the average, maximum and
minimum temperatures. With this information it
calculates the ETo using the Hargreaves-Samani
equation. The main challenge of working with the
IC51 is that it uses only 8bit numbers, thus larger
numbers had to be avoided. Also Tiny Machine Basic
does not have many mathematical functions, so, for
example, the square root function had to be carried
out resorting to a square root table nested in the
program. The program flow chart is presented in
Table 2.
Conclusion
In this work an adaptive irrigation controller was
developed and tested in a 2000m2 corn field. A rather
inexpensive PLC was used as the heart of the system
making hourly measurements of air temperature at a
height of 1.5m. These temperatures were registered
and used by the PLC to calculate daily reference
Evapotranspiration from a corn-field. These values
were then converted to ETc, using the methodology
and Kc values originally proposed by FAO56.
The program then used this information to
calculate the exact depth of water needed daily by the
crop to ensure maximum production. The irrigations
were carried out using a drip system, with drippers
spaced at 0.2m and a flow rate of 1ls-1.
The first year results were satisfactory indicating a
12% water saving, along with some increase in crop
yield, when compared to irrigation with a fixed water
depth using a standard irrigation controller.
It was observed that in the particular case of corn,
the use of Crop Coefficient values is very important,
as it leads to significant water saving at the beginning
and end of the growth season.
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