Irrigation Scheduling Methods

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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
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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
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Simple Visual observations Measure
current moisture status   Maintain soil
water budget of the root zone
Automatic irrigations Complex 
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Visual observations for scheduling Crop is
at a specific growth stage Crop is
experiencing water stress Water is available
to irrigate Neighbor is irrigating  
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 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  
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Gypsum blocks
From Scheduling irrigations by electrical
resistance blocks M. Alam, D. Rogers. Kansas
State Extension Service
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Tensiometers
From Tensiometer use in scheduling irrigation.
M. Alam, D. Rogers. Kansas State Extension
Service
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 Implementation Read sensors once or twice a
week Initiate irrigation when measurements
approach a critical level Irrigate until
water reaches a the lower depth  
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  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
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 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
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 Implementation of soil water budgeting
Irrigate when soil water reaches a critical level
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 Implementation of soil water budgeting
Must Measure to know what you have to Manage
Probe
Flowmeter
Irrigation amounts
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 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 !
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Automatic irrigations based on predetermined
conditions measured soil moisture level in
root zone water potential of the
plant computed soil water depletions program
med time
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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
 
 

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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