Baseline Systems BaseStation 3200 - Manual (Page 11)

BaseStation 3200 Advanced Irrigation Controller Manual
To understand soil moisture based smart irrigation, you also need to understand the following industry standard
terms for soil moisture content.
Dr
ie
r
W
et
ter
Saturation The soil pores are filled with water and nearly all of the air in the soil has been
displaced by water. Gravity exerts force on the water contained in saturated
soils, moving it deeper into the ground (if possible). When this “gravitational
water” moves down through the soil, it becomes unavailable to plants.
Field Capacity The level of soil moisture left in the soil after drainage of the gravitational
water. If you irrigate to a level above field capacity, it will result in runoff or
drainage as gravitational water.
Maximum
Allowed
Depletion (MAD)
When the soil moisture content reaches this level, irrigation needs to start. In
most cases, the maximum allowed depletion level is well before the plants
begin to show visible signs of stress. Irrigators typically start watering at or
before MAD is reached because they do not want their landscapes to show signs
of stress.
Permanent Wilt
Point
The minimal point of soil moisture where the plants wilt and begin to die off.
Oven Dry When soil is dried in an oven, nearly all water is removed. This moisture content
is used to provide a reference for measuring saturation, field capacity, and
MAD.
One key point is that water applied above field capacity is generally wasted – it gravitationally moves down
through the soil and becomes unavailable to plants. Excess water will also leech nutrients from the soil into deeper
soil layers, reducing the efficiency of fertilizers and soil treatments.
To understand field capacity, it is often useful to think of a sponge. If you dunk a sponge in a bucket of water and
pull it out, water will gravimetrically drain from the sponge for a period of time. When the dripping stops, the
sponge will still be very wet. This moisture level is roughly equivalent to field capacity in soils – water is no longer
draining into lower soil layers and is held in the root zone of the plants.
When your irrigation system maintains soil moisture content between field capacity and maximum allowed
depletion, you will find that your plants are healthier and your water use actually decreases. Studies also show that
appropriately varying the time between irrigation events in order to allow the soil to dry to the chosen depletion
point promotes deeper root growth and subsequently more efficiency and drought tolerance from the plants.
How to Use Soil Moisture Sensors Successfully
The first key for success with soil moisture sensors is to consider the hydrozones that exist in your landscaping. A
hydrozone is a grouping of plants that have similar water usage and delivery characteristics and can be watered
the same. For example, each of the following landscaping areas is a separate hydrozone:
• Grass in full sun with rotors
• Grass in full sun with sprays
• Drip zones in full sun • Grass in shade with rotors
• Grass in shade with sprays
• Drip zones in shade
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