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Tools for Practical Irrigation Scheduling
R. Troy Peters, Ph.D., P.E. Washington State University Irrigated Agriculture Research and Extension Center Prosser, WA
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Irrigation Scheduling Everybody Wins!
Better Yields. Better Crop Quality. Use less water. Save power Water available for alternative uses. Less leaching of water, nutrients, pesticides. Improved environmental quality.
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Water In = Water Out + ΔStorage
Soil Water Balance Water In = Water Out + ΔStorage
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Soil Water Balance
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Soil is a Water & Nutrient Reservoir
Soil Water Content (soil moisture measurement) Wilting Point (empty) Field Capacity (full) Deep Percolation = Overflow Irrigation or Precipitation = Water In ET = Water Out Water Holding Capacity (AW * Rz) = Size of Reservoir
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Field Capacity (FC): Maximum amount of water that a soil can hold indefinitely against gravity (% of volume) Permanent Wilting Point (PWP): The amount of water remaining in the soil after plants can no longer pull water from the soil (wilt & die) Available Water (AW) = FC - PWP
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Soil Texture and Available Water
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How Big is Your Reservoir?
2/25/2018 How Big is Your Reservoir? How much water can it hold? When will it be empty? Deep Silt Deep Sand ET ET Question: Which soil needs MORE water? Answer: The plants use the same amount of water regardless of soil type. Question: Where will you see water stress first? Sand. Answer: This is why people think that sandy soils need more water. Not true. Need more FREQUENT water, in smaller amounts. Question: If you have variable soil types in a single field and you want to manage for maximum production (no stress) which soil type should you manage to? (Where should you place your sensors?) Answer: Shallow sand, or lowest water holding capacity. Question: If you want to impose water stress (red wine grapes), plants in which soil type will respond most quickly? Answer: Shallow sand Question: In which soil type are you going to have trouble imposing water stress? Answer: Deep silt. Shallow Silt Shallow Sand ET ET Template B-curves
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after a few days of water use.
Starting from full, after a few days of water use. Sand Silt ET ET
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Production Reduction Function
FC MAD PWP
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Crop MAD (%) Alfalfa Apples Asparagus Corn Hop Mint Potato Winter Wheat 65 50 35
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ETc = ETr x Kc Estimate ET ETc = crop evapotranspiration
ETr = evapotranspiration rate of a reference crop (alfalfa). Function of the weather. Kc = crop coefficient. Function of the plants.
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ET and Weather ET (inches/day) Date 4/10 5/10 6/09 7/09 8/08 9/07
10/07 Date 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 ET (inches/day)
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Variation in Crop Water Use
Growing Season Crop Water Use Average Crop Water Use Germination and Emergence Vegetative Growth Reproduction (seed set) Maturity Senascence Variation in Crop Water Use from growing season to growing season
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Good Irrigation Management
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Poor Irrigation Management
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Simple soil water balance based on ET.
Designed for use on a smart phone, but usable on any desktop web browser. Designed for usability #1. Quick & easy to set up. Automatically pulls ET data from selected weather stations. Can run on any weather network who’s data can be automatically accessed.
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Don’t ask farmers questions they don’t know or have to look up.
Make is simple enough that they can play with the inputs. Tools they will use = Simple and Robust.
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Android App is functional.
iPhone App will be ready by Spring.
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Current Use
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Specific help link on every screen
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Apple iPhone iPad iPod weather.wsu.edu/ism in Safari Then…
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Then
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Looks and behaves like an app! runs in Safari
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Android
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Android Google Play Store
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Additional Features Copy settings from an existing field for quick setup or reset for new year. One-week ETc forecast NWS max & min forecast & Hargreaves eqtn. Can use hrs of irrigation run time instead of inches of applied water. Integrated calculators to help calc app. rate. Correction for dry, un-irrigated inter-rows (adjustment to water holding capacity)
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Additional Features Option for notifications via email or text.
Download all data to a .csv from full-page. Use reporting. Shows what users do and when. Can set up different crop defaults for different states, or climatological regions. i.e. can make it state-specific. Crop Kc, growth dates, MAD, Free and Open source. (PHP, MySQL)
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Feedback Growers are generally pleased with it and are using it on their own. Setting up and customizing for own field is important. Need to keep up with entering irrigation events (record keeping).
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http://weather.wsu.edu/ism R. Troy Peters, Ph.D., P.E.
Questions? R. Troy Peters, Ph.D., P.E.
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