■ Critical Management Issues for
SDI Systems in North Carolina
Although subsurface drip irrigation (SDI) is in its infancy in North Carolina, it is
becoming more popular as growers learn of its many benefits, which include in¬
creased irrigation efficiency. Proper management is imperative with an SDI system.
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Some management areas, such as water
management (irrigation scheduling) and
chemigation management (applying chem¬
icals and fertilizers through your irrigation
system), are similar to above ground drip
systems. But other management practices
are especially important or unique to SDI.
Many components of an SDI system are
underground; therefore, you must carefully
monitor pressure and flow rates to ensure
that the system is operating properly.This
publication addresses water management,
chemigation, system management and
maintenance, and system evaluation.
Water Management
Water management, often referred to as
irrigation scheduling, is the process of de¬
termining when and how much to irrigate.
Factors influencing your decision to ir¬
rigate include weather, crop, soils, system
design, and management criteria (yield
goal, labor, convenience, water supply,
etc.). Irrigation scheduling techniques pro¬
vide information on how much to irrigate,
or when to irrigate, or both.
Techniques that determine how much to
irrigate are typically called water balance
or checkbook methods. They are based
upon replacing water that has been lost to
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soil evaporation and plant transpiration,
often lumped together and called evapo-
transpiration (ET). You may also lose
water to deep percolation (drainage) and
runoff. Inputs of water to the soil system
are irrigation and rainfall. Water balance
methods try to balance incoming and out¬
going soil water so that water is available
for crop growth.
Techniques that determine when to ir¬
rigate typically measure stress points in
soil or plants, and require additional soil
and crop information to determine how
much to irrigate.
An SDI system can apply water in rela¬
tively small amounts and can be operated
to replace the water several times a day
as it is used by the crop. Multiple small ir¬
rigations per day are more appropriate for
high value vegetable crops.
Water Balance Scheduling Methods
The water balance or checkbook method
requires that you estimate evapotrans-
piration, measure rainfall, and record
irrigation amounts. Irrigation and rainfall
replace water lost to ET. Irrigation and
rainfall in excess of what the soil can hold
are lost as deep percolation or runoff
and are not credited towards replac-
