Base Line BaseStation 3200, User Manual, Page: 17 / 102

BaseStation 3200 Advanced Irrigation Controller Manual
Page
9
Understanding Soak Cycling
When you set up your irrigation programs, remember that the rate at which the irrigation application devices
apply water might be very different than the rate at which the soil in your landscape can take up that water.
Soak cycling breaks the total run time into shorter water “cycles” with “soak” periods in between to allow time for
water to soak into the soil.
Precipitation Rates vs. Infiltration Rates
The precipitation rate, which is the rate at which sprinkler heads or drip emitters apply water to the soil, is typically
measured in inches, like rainfall.
Many soils only allow water infiltration at a rate of .25 inch per hour or less, whereas most head types put down
.50 inch per hour or more (much more in the case of some spray heads).
Also remember that head spacing and overlap directly influence the total precipitation rate for any specific zone.
Precipitation Rates for Common Sprinkler Types
Spray Heads 1.00 inch to greater than 5.00 inches per hour
Gear Driven Rotors 0.25 inch to 0.65 inch per hour
Multi-stream Rotors 0.40 inch to 0.60 inch per hour
Drip Emitters Depends on area covered, rarely exceeds infiltration rate
Estimated Infiltration Rates for Common Soil Types
Course Sand 0.75 inch to 1.00 inch per hour
Fine Sand 0.50 inch to 0.75 inch per hour
Find Sandy Loam 0.35 inch to 0.50 inch per hour
Silt Loam 0.15 inch to 0.40 inch per hour
Clay Loam 0.10 inch to 0.20 inch per hour
As you can see from the tables above, most sprinkler heads have higher precipitation rates than the infiltration
rate of most soils.
When the irrigation schedule puts down more water than the soil can take up, the excess water will typically run
off to the lowest point, leaving some areas of the landscape, or even the entire irrigated landscape, under
watered. Standing water also evaporates at a fairly high rate, especially in the heat of the summer months, further
reducing irrigation efficiency.
Even on a perfectly designed system, it is important to match the water application rate to the infiltration rate of
your soil. You can achieve this balance by breaking a total run time for any zone into multiple “cycles” (timed water
applications) and “soaks” (timed wait periods for the water applied in the last cycle to infiltrate into the soil before
applying more water).
The BaseStation 3200 has built-in support for soak cycling and has intelligent watering algorithms that apply cycles
in the optimal order to maximize water penetration and minimize evaporation loss.
Note: Soak Cycling is required on all soil moisture based zones or scheduling groups in order to ensure that the
applied irrigation water is reaching the moisture sensor.
As a rule-of-thumb, Baseline recommends that you break the total run time for any zone into at least 3 cycles, and
configure the soak time between cycles to be at least twice the length of the cycle time.