Quick Facts....
- Subsurface drip (SDI) is a low-pressure, low-volume irrigation system
that uses drip tubes buried below the soil surface.
- Subsurface application of water aimed directly at the root zone improves yields by reducing the incidence of disease and weeds.
- SDI is suitable for almost all Crops and especially for high-value
fruit and vegetable Crops, turf and landscapes.
- Research shows the yield and quality of produce improves with a buried drip system. Normal life expectancy of a system is 12 to 15 years.
Subsurface drip (SDI) is a low-pressure, low-volume irrigation system
that uses buried drip tubes. Farm operations become free of impediments
that normally exist above ground with any other pressurized irrigation
system.
Subsurface application of water aimed directly at the root zone improves yields by reducing the incidence of disease and weeds. Germination of annual weed seed is reduced, which lowers weed pressure. Water is conserved, fertilizer efficiency is enhanced, and labor needs are reduced. In addition, field operations are possible, even when irrigation is applied.
The applied water moves by soil matrix suction, eliminating the effect
of surface infiltration characteristics and saturated condition of ponding
water during irrigation. Application is uniform and highly efficient.
Wetting occurs around the tube and water moves out in all directions.
A subsurface-drip or microirrigation system is flexible and can provide frequent
light irrigations. This is especially suitable for arid, hot and windy
areas with limited water supply. Since SDI is under the surface, repairing
tubes is difficult and cumbersome. Rodents tend to chew the tubes therefore
precaution should be taken to prevent rodent damage. Clogging is not apparent.
Close monitoring of the system is a must.
Crops
SDI is suitable for almost all crops. It is used mostly for high-value fruit
and vegetable crops, turf and landscapes. Strawberry, tomato, potato,
cantaloupe, onions and other vegetables have shown increase in yield,
both in quantity and quality. Cantaloupe tends to mature early and uniformly.
Rots, molds or blemishes from hard water are eliminated. Alfalfa regrowth
after a cut may be encouraged by subsurface irrigation without allowing
shallow-rooted weeds to emerge. Spacing of the burial tubes is a critical
issue for normal crops such as alfalfa.
Materials
A large variety of drip tubes are available on the market. The polyethylene tubes have built-in emitters set at certain
intervals along the tube. Water drips out of the emitter opening at the end of a turbulent pathway, where the pressure is
dissipated and water just dribbles out.
The spacing and the flow rate of the emitters in subsurface drip tubes
are variable according to the product. Products are available at variable
wall thickness. The higher the MIL number, the thicker the wall, which
extends the life of the tube. The cost also goes up with the increase
in wall thickness. The polyethylene tubes fitted with pressure-compensating
emitters make them suitable to distribute water uniformly in sloping fields.
Pressure differential due to ground slope is avoided. Naturally, these
tubes cost more.
Layout
A typical system layout consists of a settling pond (where possible), pumping unit, a hydrocyclone separator (when a pond
is not feasible to take out the coarse materials), chemical injection unit, filtration unit equipped with back-flush control
solenoid valves, pressure regulators, air vent at manifold, and PVC delivery system to carry the water to the field.
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Figure 1: A typical subsurface microirrigation field layout.
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The delivery system is composed of main, submain and manifold, to which
the lateral drip tubes are attached. Optional items like a flow meter
and a pressure gauge are essential to monitor the performance of the system.
It is essential to provide an air release/vacuum breaker valve at the manifold
for easy drainage of the tubes when the pump is shut off. Determine valve
placement according to the topography. The air release valve should be
placed at the highest point of elevation at the delivery pipes. This will
allow release of trapped air. The vaccum breakers help prevent suction
development due to the partial vacuum created as the water leaves the
tube. In a freshly installed system, the loose soil may settle around
a collapsed tube, making it difficult for the tube to regain its shape
in absence of an air vent. A typical field layout is shown in Figure 1.
Placement
The tubes are injected below the soil surface, using an attachment pulled
by a tractor. The placement depths vary from six to 24 inches, depending
on the soil and crop. Shallow-rooted crops, like strawberries, may require
placement at six to 10 inches below the surface, depending on soil type:
capillary water movement is limited in sandy soils therefore shallow placement
is recommended. In heavier soils, water moves upward easier and can reach
higher levels thus tubes can be placed deeper. The emitters on the tube
should face upward at installation. Placement at a uniform depth is essential
and proper soil moisture facilitates the process.
Filtration
It is essential to have a filtration unit that will filter all the particles
that are bigger than the emitter openings. A 200 mesh filter is usually
adequate for most types of emitters. Filtration can be viewed as the heart
of a SDI system and should be designed properly to fit the level of contamination
of the water source. Filtration may not be a concern where domestic water
is used around the house or in city landscaping.
Operation and Maintenance
The performance and life of any system is dependant on how well it is designed and operated. When operated by automatic
controls, the system needs to be inspected from time to time. The back-flush system needs to be checked and the laterals
flushed at regular intervals.
The quality of water affects the system. High pH water will tend to precipitate calcium salts. High salinity or iron will cause precipitates. The situation is aggravated by organic matter, bacteria and algae present in the water. The scum material formed by the combination of organic matter and fine clay particles may clog the emitters. Deep well water may be free of scum, but the pH need to be checked to avoid precipitate.
Occasional injection of acid, acid-forming chemicals or chlorine may help to stop precipitate and scum formation.
N-phuric, a commercial mixture of acid and N-fertilizer available in the market,
may be useful. In addition to lowering the pH to reduce precipitate formation,
the product will provide nitrogen fertilizer to the crop. The system should
run for awhile after injection of any chemical to remove residual chemicals.
It is essential to winterize the system at the end of the cropping season
by thoroughly draining all pipes and appurtenances. An air compressor
may help blow out the residual water, especially from the above ground
fixtures. Polyethylene tubes are flexible and won't break due to freeze.
Rootguard products may be used to prevent root growth into the emitter
openings which can cause clogging.
Cost
A subsurface drip system may require higher initial investment and cost will
vary due to water source, quality, filtration need, choice of material,
soil characteristic and degree of automation desired. System cost, including
installation, may range from $800 to $1500 per acre.
Research consistently shows yield and quality of produce improves when a buried
drip system is used. Normal life expectancy of a system is considered
to be 12 to 15 years. The system may remain buried in the ground for many
years.
References
For information on irrigation management and scheduling. see Colorado State University
Extension fact sheets:
Additional Information on the Web:
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