Irrigation Scheduling. 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/. 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/
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
Why Schedule • Prevent stress – health of plant - yield loss – appearance • Maximize water use efficiency – beneficial use of resource • Minimize leaching of nitrates or pesticides
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
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 50%=1
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
ET Measurements • Weighing Lysimeters • Uniformity of soil important • Representative plant growth
For Annual Crops • Depth of root zone increases during the growing season • Allowable soil moisture depletion varies with each stage of plant growth
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
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/cropsystems/DC1322.html • “SCS-Microcomputer Irrigation Scheduling Package” 1992 • Computer simulations