Irrigation Scheduling MethodsIrrigation Scheduling Methods

Gerald Buchleiter

USDA-ARS Water Management Unit

Fort Collins, CO

NRCS Irrigation Water Management Training

What is Irrigation Scheduling?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

•Flexibility of system to deliver water •Level of control available to the irrigator

e.g. ditch system on a fixed schedulevs. 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

Factors to consider

Can range from

qualitative ‘feeling’ that need to apply water to prevent damaging crop stress

  to

quantitative soil water budgets forindividual fields at various levels of detail

Irrigation scheduling methodsIrrigation scheduling methods

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 crope.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 budgetingImplementation 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 ProbeIrrigation amounts

 Implementation of soil water budgeting Implementation of soil water budgeting Computerized scheduling program

•Same basic procedure as ‘checkbook’

•Obtain data from weather network

•Forecasts futurecrop 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