Irrigation Scheduling Methods
NRCS Irrigation Water Management Training
Gerald Buchleiter
USDA-ARS Water Management Unit
Fort Collins, CO
What is Irrigation Scheduling?
• Using information to make a decision about
when and how much water to apply
• Can range from general information about a
broad region to very specific information about
areas of a field
Factors to consider
•Flexibility of system to deliver water
•Level of control available to the irrigator
e.g. ditch system on a fixed schedule
vs. large capacity well supplying sprinklers
•Ability to match water needs with available supply
•How often an irrigation decision is made
e.g. monthly, weekly, daily, hourly
•Availability of data and time to make decisions
Irrigation scheduling methods
Can range from
qualitative ‘feeling’ that need to apply water
to prevent damaging crop stress
to
quantitative soil water budgets for
individual fields at various levels of detail
Simple
•Visual observations
•Measure current moisture status
•Maintain soil water budget of the root zone
•Automatic irrigations
Complex
Visual observations for scheduling
•Crop is at a specific growth stage
•Crop is experiencing water stress
•Water is available to irrigate
•Neighbor is irrigating
Measure current status
•Soil moisture sensors indicate water availability
in the root zone
e.g. gypsum blocks, granular matrix probes,
tensiometers, capacitance probes,
•Sensors indicating the water status of the crop
e.g. IR thermometer for canopy temperature
Gypsum blocks
From “Scheduling irrigations by electrical resistance blocks”
M. Alam, D. Rogers. Kansas State Extension Service
Tensiometers
From “Tensiometer use in scheduling irrigation”. M.
Alam, D. Rogers. Kansas State Extension Service
Implementation
•Read sensors once or twice a week
•Initiate irrigation when measurements
approach a critical level
•Irrigate until water reaches a the lower
depth
Maintain soil water budget of the root zone
•Daily reference ET based
on weather data
•Crop coefficients for actual ET
•Measure rainfall
•Forecast daily water use for next 1-2 weeks
•Compare computed w/ measured soil moisture
Implementation of soil water budgeting
•Manual ’Checkbook’ method
Soil water is the ‘account balance’
Irrigation and rain are the ‘deposits’
ET, percolation, runoff are the ‘checks’
Implementation of soil water budgeting
Irrigate when soil water reaches a critical level
Implementation of soil water budgeting
Must Measure to know
what you have to Manage
Flowmeter
Irrigation amounts
Probe
Implementation of soil water budgeting
Computerized scheduling program
•Same basic procedure as ‘checkbook’
•Obtain data from
weather network
•Forecasts future
crop use
Irrigate when soil water reaches a critical level
Measure amounts !
Automatic irrigations based on
predetermined conditions
•measured soil moisture level in root zone
•water potential of the plant
•computed soil water depletions
•programmed time
Quantifying expected benefits
•Improved yields with less water
(include rain to make annual comparisons)
•Reduced energy costs if pumping
•Reduced leaching of nutrients
(less fertilizer required)
•Improved crop quality
(more timely irrigations)
•More efficient utilization of labor
Selecting a method
•Availability of data to determine crop water use
•Ability to measure water applied
•Time required to make better decisions
•Value of expected benefits