Factors to consider •Level of control available to the irrigator •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

Must Measure to know what you have to Manage  Implementation of soil water budgeting Must Measure to know what you have to Manage Flowmeter Irrigation amounts Probe

Measure amounts ! 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