Adaptability and Suitability of Microirrigation

Based upon analyses provided by Pair et al. [96], Keller and Bliesner [11], and Papadopoulos [122], advantages and disadvantages of microirrigation systems include:

Advantages

Microirrigation has the following advantages:

• It has the potential to reduce irrigation water use and corresponding operating costs because water can be applied only where the crop roots develop. This is particularly true for widely spaced crops such as orchards and vineyards or for shallow-rooted crops.

• It has been shown to increase the yield and quality of some crops. This is most likely the result of maintaining near-optimum water and fertility conditions in the root zone.

• It can reduce the cost of labor because the systems need only to be maintained and managed, not tended. Operation usually is accomplished by automatic timing devices, but the emitters and system controls should be inspected frequently.

• A greater control over fertilizer placement and timing through fertigation with microirrigation improves fertilizer efficiency and reduces pollution hazards associated with fertilizers.

• It can reduce weed growth and the incidence of some diseases because foliage and much of the soil surface are not wetted. This reduces costs of labor and chemicals to control weeds and diseases and reduces related pollution hazards.

• It is less disruptive to field operations because the noncropped soil between crop rows is not wetted.

• Frequent irrigations maintain soil water content and keep the salts in the active root zone more dilute, making it possible to use more saline water than with other irrigation methods.

• Well-designed microirrigation systems can operate efficiently on almost any topography.

• Problem soils with low infiltration rates, low water-holding capacity, and variable textures and profiles can be irrigated efficiently.

• It usually requires lower operating pressure and thus less energy than sprinkler systems.

Disadvantages

Microirrigation has the following disadvantages:

• Equipment costs usually are higher than for surface irrigation systems and may be higher than for sprinkler systems.

• Equipment often is complex and requires frequent monitoring to ensure good performance.

• Energy costs to pressurize the system are higher than with surface irrigation.

• Because emitter outlets are very small, they can become clogged by particles of mineral or organic matter. Clogging reduces discharge rates and the water distribution uniformity; thus filtration is required in most cases. Iron oxide, calcium carbonate, algae, and microbial slimes may be problems requiring chemical treatment of the water to prevent clogging.

• Because microirrigation systems operate at low pressures, varying field topography can result in significant pressure variations and irrigation nonuniformity. Careful design and pressure regulation are required on undulating land.

• Some crops do not germinate well with drip irrigation and especially with subsurface drip. A second method of irrigation, usually portable sprinklers, may be required for germination.

• Salts may concentrate at the soil surface and between emitters and become a potential hazard. Localized salt accumulation can hinder crop germination. Light rains can leach accumulated salts downward into the root zone. Irrigation should continue on schedule unless adequate rain has fallen to ensure leaching of salts below the root zone.

• Salts also concentrate below the surface at the perimeter of the wetted bulbs. Too much drying of the soil between irrigations may allow the movement of water and salts back toward the inner bulb. To avoid this damage, irrigation must be frequent under saline conditions.

• If unexpected events (equipment failure, power failure, or water-supply interruption) interrupt irrigation, crop damage may occur quickly because roots use only a small volume of wetted soil. At least 33% of the total potential root zone should be wetted. Careful system maintenance and a secure water supply are a must.

• When a main supply line breaks or the filtration system malfunctions, contaminants may enter the system, resulting in emitter clogging. Secondary filters can be used to protect against these problems.

• Rodents and other small animals sometimes chew and damage polyethylene tubing. In some cases, animal damage disallows laying tubing or emitters on the soil surface. Burrowing rodents also may damage subsurface tubing. Rodent control may be necessary to reduce the problem.

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