DEVELOPMENT AND TESTING OF AN AUTOMATED SOIL MOISTURE SENSING DRIP FERTIGATION SYSTEM

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DEVELOPMENT AND TESTING OF AN AUTOMATED SOIL
MOISTURE SENSING DRIP FERTIGATION SYSTEM

• Jonathan H Schroder
• Rafael Muñoz-Carpena, Yuncong Li

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High efficiency irrigation

• Traditional methods of applying large amounts of
  water at a low frequency often result in much of
  the water being lost through percolation on the
  coarse soil common to florida
• The solution??
• Combine scientific methods for improving
  irrigation efficiency and management

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The challenge
This portion of water (50) is easily drained
from the soil during excess irrigation

• Irrigation design is very dependant on the water
  holding characteristics of the soil.
• Florida soils commonly have low water holding
  capacity (sands and gravels).
• The soils of South Florida made artificially by
  crushing the coral surface (Krome soil has 51
  coarse particles gt 2 mm).
• These soils present challenges for agriculture

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High frequency low volume (HFLV) irrigation

• Our recommendation for an efficient and modern
  irrigation system for these areas are based on
  THREE PRINCIPLES
• 1)       high-frequency/low volume (several
  times per day)
• 2)       soil moisture sensors for scheduling
  (give water when the plant needs it)
• 3)       automatic operation
• One added benefit of high frequency, soil
  moisture-based automated irrigation is
  convenience. Once the system is properly
  installed, normally only minimal supervision is
  required.

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Irrigation and fertilizer management

• Irrigation and fertilizer management are
  interlinked. This is very important, as changes
  in one will affect the efficiency of the other!
• Poor irrigation management will reduce nutrient
  use efficiency

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QIC and capacitance soil moisture probe

• Irrigation events are preset in the irrigation
  controller.

• The soil moisture probes do not initiate an
  event, it only determines if an event is needed
  according to soil moisture status.
• It gives a yes or no to a predetermined event

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Quantified Irrigation Controller
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Field experiments

• 3 field trials were conducted on plastic mulched
  tomatoes to test the soil moisture-based
  scheduling and QIC
• South Florida (Homestead) during the 2003/2004
  winter season (gravelly loam)
• So.FL-TREC again during the 2004/2005 winter
  season (gravelly loam)
• North Central Florida (Citra) during the 2005
  spring season (fine sand)

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Objectives of experiments

• To test for irrigation water savings and
  fine-tune the new soil moisture-based scheduling
  methodology
• To quantify any reduction in nutrient leaching
  from the root zone using the soil moisture-based
  scheduling.
• To successfully manage fertilizer by fertigation
  coupled with the soil moisture-based scheduling
  system

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Exp. 1 So FL 2003-2004

• The QIC system was set at two thresholds of
  Low400 mV and High 450 mV, corresponding to the
  soil moisture level at 25 and 10 cbar
  respectively, for the gravelly-loam soil of the
  area

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Field lay-out
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Results Water Use
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Results Yields
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Exp. 2 So FL 2004-2005
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Lysimeters
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Field pumphouse layout
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Pump house
Pressure tank
Venturi injectors
Backflow protection
Mess
Fire-ants
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Results Water use

• Large savings occur early in the season

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Results Yields
Different letters depict statistically
different means for P 0.05 (Holm-Sidak
method) z Total water per treatment includes
the hour per day of establishment irrigation
which was treatment independent

• Irrigation water use efficiency (IWUE) is
• IWUE (Y Yd)/Irr
• Where Y the total marketable yield
• Yd the dryland marketable yield (approx 0)
  
• Irr the water applied by irrigation

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Results Nutrient Leaching
Different letters depict statistically
different means for P 0.05 (Holm-Sidak method)
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Exp 3 Field preparation

• LAYING OUT RAISED BEDS

• Cleaning and burying lysimeters

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Field Equipment
Black plastic mulch beds
Lysimeters
Pumphouse
55 cm
85 cm
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Data acquisition

• Recording Soil Moisture and checking probe
  settings

• Sampling lysimeters

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Results water IWUE

• I1 -gt 10 water saving I2 -gt 64 water savings
  over I4

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Results Nutrient Leaching
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Summary of results

• () farmer IWUE in parenthesis

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Conclusions

• Significant water savings were recorded on both
  soils for the soil moisture cut-ff systems.
• Dielectric soil moisture sensors required less
  maintenance than tensiometers on the fast
  draining soils
• Reduced leaching ( gt58) of N and P fertilizer
  was achieved by the soil moisture-based
  scheduling

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Dicussions and limitations

• One tensiometer or ECH2O probe per treatment.
  -gt A single probe may not be representative due
  to soil, plant, probe position or irrigation
  inconsistencies
• The leached nutrient results depend heavily on
  the accurate placement of plants and emitters
  relative to the lysimeter
• Not an established system and technology yet, and
  trust in the performance still needs to be
  developed,
• BUT the system has high potential as can be seen
  from the results!

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Acknowledgements

• USDA-SARE for its Research Grant, no. LS03-148
• Matching Assistantship from the Dean of Research
  Office
• Tina Dispenza and Harry Trafford for their help
  in many trips to Lovett Irrigation Store