Exercises Case study pesticide leaching in field soil

1
Exercises Case study pesticide leaching in
field soil
2
Case Study on Pesticide leaching

• In this case study we will use the data of Groen
  (1997) on pesticide leaching at a sandy loam
  experimental field.
• Similar to other case studies, first a reference
  situation is defined. Next various input data and
  simulation options are changed (scenarios) and
  their effect on pesticide transport analyzed.
  Besides getting more acquainted with the
  possibilities of SWAP, the scenarios were
  selected to provide more insight in the relative
  importance of various processes.

3
Data and Options

• The following input data and simulation options
  are considered
• 1. Reference situation
• 2. Dispersion
• 3. Adsorption
• 4. Temperature
• 5. Application time
• 6. Seepage
• 7. Meteorological year
• 8. Preferential flow due to immobile water
• 9. Cracked clay soil

4
Reference Situation

• The experimental field is situated near Creil in
  the Noordoostpolder, which was reclaimed from the
  former Zuider Zee.
• The soil profile consists of 90 cm loamy sand on
  top of a 30 cm detritus-gytta layer with a low
  permeability.
• Underneath the detritus-gytta layer a sandy
  aquifer occurs, which interacts with the phreatic
  groundwater.

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Reference Situation

• Table 1 lists the soil hydraulic parameters of
  the 4 distinguished soil layers.

6
Reference Situation

• On top of the detritus-gytta layer subsurface
  drains were installed with a spacing of 4 m.
  Using groundwater level and drainage rate data,
  Groen (1997) determined the interaction between
  the phreatic groundwater and the groundwater
  underneath the semi-confining detritus-gytta
  layer.
• The resistance of the detritus-gytta layer
  amounts 75 d, and the average hydraulic head in
  the underlaying aquifer 85 cm below soil surface.

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Preparing Data of Reference Situation
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Reference Situation

• We will consider the period September 1989 until
  August 1990, and define September as the first
  month of the agricultural year.
• The simulation is started in autumn, as
  pesticides applied in autumn in North-West
  European climate have the highest risk of
  percolation to groundwater and leaching to
  surface water in the subsequent winter period.

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Reference Situation

• The meteorological data consist of daily
  reference evapotranspiration (weather station
  Lelystad) and on-site rainfall data. In the
  considered period tulips were grown, which were
  planted in October and started to grow in
  February.
• In June the tulips started to wither, and at the
  beginning of July they were harvested.

10
Reference Situation

• Detailed data on leaf area index, soil cover,
  rooting depth, and the root water uptake function
  are included in the file 'Tulip.crp' on the
  directory 'Pesticid'.

11
Reference Situation

• The properties of the pesticide Metamitron were
  determined in the laboratory (adsorption,
  decomposition) and fine-tuned by calibrating SWAP
  simulations with Metamitron concentrations
  measured in the soil and drainage water during
  field experiments. Table 2 lists the fine-tuned
  transport properties of Metamitron, which will be
  used in current simulation. Usually Metamitron
  is applied in spring-time, however for
  illustrative purposes we will simulate a large
  application in autumn time (7 November, 169.5 kg
  ha-1).

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Reference Situation

• Metamitron decomposition is sensitive to soil
  temperatures. Groen (1997) showed that measured
  soil temperatures were well approximated by a
  sinusoidal temperature wave with parameters as
  listed in Table 3.

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Tap - General
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Tap - Timing
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Tap Sub-run(s)
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Tap Run options
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Checking, Saving, Exiting
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Running
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Output preparation
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Output water balance
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Output solute balance
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Preferential flow changing