1. Tools for Practical Irrigation Scheduling
R. Troy Peters, Ph.D., P.E.
Washington State University
Irrigated Agriculture Research and Extension Center
Prosser, WA

2. 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.

3. Water In = Water Out + ΔStorage
Soil Water Balance
Water In = Water Out + ΔStorage

4. Soil Water Balance

5. 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

6. 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

7. Soil Texture and Available Water

8. 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

9. after a few days of water use.
Starting from full,
after a few days of water use.
Sand
Silt ET ET

10. Production Reduction FunctionFC
MAD
PWP

11. Crop
MAD (%)
Alfalfa
Apples
Asparagus
Corn
Hop
Mint
Potato
Winter Wheat 65 50 35

12. 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.

13. 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)

15. 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

17. Good Irrigation Management

18. Poor Irrigation Management

19. 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.

20. 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.

21. Android App is functional.
iPhone App will be ready by Spring.

24. Current Use

37. Specific help link on every screen

38. Apple iPhone iPad iPod weather.wsu.edu/ism in Safari Then…

39. Then

40. Looks and behaves like an app! runs in Safari

41. Android

42. Android Google Play Store

45. 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)

46. 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)

47. 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).

48. http://weather.wsu.edu/ism R. Troy Peters, Ph.D., P.E.
Questions?
R. Troy Peters, Ph.D., P.E.