Baseline Systems BaseStation 1000 - Manual (Page 9)

BaseStation 1000 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
te
r
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.
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