Page 228 - Biosystems Engineering

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percolate more vertically. Therefore, selection of the type of drip emit-
ter and its placement is very important. Drip systems operate under
low pressure and use capillary-sized channels within the emitter to
control the flow rate. However, this leads to clogging of the emitters.
Therefore, drip systems are designed with filtration systems to remove
suspended sediments. Water quality is also of major concern due to
the formation of salt deposits in the emitters, which alter the hydraulic
flow characteristics of the emitter. The water needs to be chemically
treated to prevent salt precipitation. The flow though the emitters is
controlled by the pressure of water within the lateral at the location of
the emitter. Biosystems engineers have designed emitters that have
pressure-compensating mechanisms, which maintain a similar flow
rate even under a large variation in water pressure.

Subsurface Irrigation Systems
This is the most advanced irrigation system with water application
efficiencies as high as 95 percent (ASAE 1990). The water is applied
directly into the root zone via porous pipes. Because the plant root is
directly wetted in the root zone, the plant canopy does not get wet.
This reduces the incidence of diseases, which are common in high-
humidity conditions associated with wet canopy. Just as in drip
irrigation systems, subsurface irrigation systems also require water
filtration and chemical treatment to prevent clogging and salt
precipitation. Figure 6.5 shows a cotton field subsurface irrigated
with porous pipes buried within the root zone. Note the absence of
weeds in the furrows due to limited availability of water.

FIGURE 6.5 Cotton fi eld irrigated by subsurface irrigation system in central
Arizona.