Irrigation Scheduling

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Irrigation Scheduling
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New Legislation

• Act 148 Water use reporting, mapping of
  groundwater information, consider need for
  addition legislation
• Act 177 Water use conflict resolution
• Governor - Water Legacy Act
• http//www.michiganlegislature.org/

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Irrigation Scheduling

• Know available soil water for each unit
• Known depth of rooting for each crop
• Know allowable soil moisture depletion at each
  stage of plant growth
• Use evapotranspiration data to estimate crop
  water use
• Measure rainfall in each field
• Use container capacity for nursery crops

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Why Schedule

• Prevent stress health of plant - yield loss
  appearance
• Maximize water use efficiency beneficial use
  of resource
• Minimize leaching of nitrates or pesticides

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Irrigation amount

• The amount of water available to the plant is a
  function of root depth and soil available water
• For example plant with a rooting depth of 2 ft
  on Coarse-textured loamy sand has .08 in/in X 2
  ft X 12 in/ft 1.98 in
• For an allowable depletion of 50 - a 1 in
  application would replenish available water

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Reference Evapotranspiration

• ETo or potential evapotanspiration represents a
  well watered, fully developed plant such as grass
• Reference evapotranspiration is multiplied by a
  crop coefficient to obtain the ET rate for a
  specific crop
• The crop coefficient varies throughout the
  growing season
• For Example Corn at 20 0.67 at 501

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Estimates of ET

• Max and min temperatures
• Relative humidly
• Wind
• Net radiation
• Modified Penman to estimate ETo
• U of Wisconsin web site
• http//www.soils.wisc.edu/wimnext/et/miet.html

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ET Measurements

• Weighing Lysimeters
• Uniformity of soil important
• Representative plant growth

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For Annual Crops

• Depth of root zone increases during the growing
  season
• Allowable soil moisture depletion varies with
  each stage of plant growth

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Methods to Estimate Soil Moisture

• Feel and Appearance
• Electrical resistance electrodes on blocks in
  soil
• Tensiometers measures soil moisture tension
• Must be measured at a range of depths in root
  zone

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Irrigation Scheduling Methods

• All methods require keeping sufficient records
• Appearance and feel of soil must look at a
  range of depths in the root zone
• Checkbook method inputs are rainfall and
  irrigation output ET Automated spreadsheet
  will be available by Jan 15
• http//www.extension.umn.edu/distribution/cropsyst
  ems/DC1322.html
• SCS-Microcomputer Irrigation Scheduling Package
  1992
• Computer simulations

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