ESP-SMT Smart Modular Control System
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Management Allowed Depletion (MAD)
This is the maximum amount of amount of Plant Available
Water (PAW) expressed as a percent that the irrigation
manager has determined can be removed from the soil
from ET before irrigation will need to occur. To promote
Plant Health and deep root growth, it is best to irrigate only
when the root zone has reached MAD. In this example, the
MAD value is 50% (see Table below); so irrigation will need
to occur when the PAW level reaches 0.51 inches (1.02” @
50%)
Managed Allowed Depletion (MAD) Table
Soil Type or Class
Available Water (AW)
(in of water per in of soil)
Sand
30%
Loamy Sand
50%
Sandy Loam
50%
Loam
50%
Clay Loam
40%
Silty Clay
40%
Clay
30%
“Checkbook” Method of Irrigation
The on-site SMT Weather Sensor constantly monitors
the weather and communicates the information to the
controller on a daily basis. Once the Accumulated Water
Requirement reaches the MAD threshold value, irrigation
will begin if it is on an Allowed Watering Day. An analogy
to this scenario is your checkbook…. rainfall is the amount
of free money going in, and ET being the money being
withdrawn; and irrigation representing a deposit that you
put into your account to bring it up to a certain threshold
value.
The Table below shows the Accumulated Water
Requirement (AWR) for the example:
Day
ET/Day
Effective
Rain
Net Water
Req’t
Accumulated
Water Req’t
1
0.18”
0.00”
0.18”
0.18”
2
0.16”
0.00”
0.16”
0.34”
3
0.16”
0.16”
0.00”
0.34”
4
0.18”
0.00”
0.18”
0.52”
5
0.14”
0.00”
0.14”
0.66
”
In the example, irrigation will occur on Day 4 as the Accumulated
Water Requirement (0.52) has reached the calculated Management
Allowed Depletion (0.51).
Replenish Accumulated Water Requirement (AWR)
The total amount of time that each zone needs to operate
is dependent on the Net Application Rate (Precipitation
Rate X System Efficiency) that the sprinkler system is
applying.
For example, if the precipitation rate for a rotor zone is 0.6
inches per hour and the efficiency is 85%, then the Net
application Rate is 0.52 inches per hour. To replenish the
AWR, the zone would need to have a total run time of 1
hour on Day 4.