Problems associated with drip irrigation systems
In spite of the major advantages described earlier. There are several problems associated with drip irrigation systems:
- (i) Emitter clogging: A major problem associated with drip irrigation systems is the clogging of emitters, unless preventive measures are taken. Emitter outlets are very small and can become clogged easily by suspended materials (sand and silt), precipitated dissolved salts (mainly carbonates), rust and other iron oxides and organic matter (including plant roots, algae and other minute animals). Clogging can reduce emission rates and cause poor uniformity of water application. Prolonged clogging can cause severe damage to the crop. Clogging also increases the maintenance costs, as it becomes necessary to check, repair or replace clogged emitters and other components. Chemical treatment and proper filtration of water can prevent or correct emitter clogging. The first requirement is to select emitter devices which may require less maintenance. Well-designed filtering systems, when properly maintained, can solve the problem caused by suspended material (sand and silt) and in some cases the organic matter. An effective means of dissolving carbonates is by means of dilute acids (mostly HNO3 or HC1). However, it will require an interruption in irrigation water application. Flushing by water or air under pressure is feasible if the pipes and joints can withstand the pressure. Pulse irrigation, namely, irrigating at a higher rate for a very short time, is effective.
- (ii) Restricted root development of crops: Drip irrigation normally wets only a part of the root zone. Hence, the root distribution is almost limited to the moist zone. Many factors, involving soil and plant characteristics, management practices (amount and frequency of water application) and the design of the irrigation system (number of emitters per plant, placement and discharge rate of emitters) influence the root development of crops. The concentrated distribution of roots may reduce the plants ability to withstand strong winds. Further, the ability of the plant to withstand drought, resulting from any breakdown in the irrigation system, is greatly reduced as water of the wetted zone gets depleted soon and the surrounding region is dry. Careful planning and operation of the irrigation system and prevention of breakdowns will reduce the magnitude of the problem.
- (iii) Salt accumulation at the root zone periphery: Where high salinity water is used for irrigation in arid regions, salts tend to accumulate towards the periphery of the wetted zone and the interface between the irrigated and non-irrigated zones in the soil. As the root zone is kept constantly at high moisture level, there may not be any major impact on the crop, but in the next growing season these salts, if not leached away, may damage the succeeding crop if planted on the interface having the salt patch. In regions where drip irrigation is practiced in the dry season with rainfall exceeding about 300 mm in the following rainy season, the salts will generally be leached. Like in other methods of irrigation, good natural or artificial drainage is needed in drip irrigated areas as well. Otherwise, artificial leaching is to be provided once every one or two years.
- (iv) Damage from rodents and other animals: There are several kinds of burrowing animals which can cause damage to surface or buried polyethylene laterals. They include rats, mice, squirrels, dogs and rabbits. When present in large numbers, these animals can cause heavy damage to drip irrigation systems by chewing holes in the lateral lines. Use of repellents to keep the animals away and baiting or trapping them are possible control measures. Rats and squirrels can be controlled by adopting subsurface drip system. Rats generally never cross a wet surface. Keeping the system moist is a possible remedy to control it. A chemical repellent which tastes or smells bad to the animal can be injected through the system or laid down with the laterals during installation. There are a number of chemicals available which are obnoxious to animals, including anhydrous or aqua ammonia and a number of insecticides which can be injected into the drip system. Rodent damage can also be prevented by the use of polyvinyl chloride (PVC) laterals. Ants and beetles can damage thin-walled polyethylene tubing. Ant damage typically takes the form of holes chewed through the sides of strip tubing and enlargement of orifices in strip tubing. Some types of insects will build a cocoon inside emitter outlets in water distribution tubing. Cocoons are built when the system is shut down for a period of time. These insects are to be controlled only during prolonged shut down periods. Ant damage can be successfully controlled with chlorinated hydrocarbon insecticides. However, these chemicals are usually toxic and persist in the environment and should be used with great care. A common recommendation is to use lateral tubes with sufficient wall thickness (not less than 15 mils (0.38 mm) to reduce damage by ants and insects.
- (v) High cost of drip irrigation systems: The cost of drip irrigation system is high when compared to surface or portable sprinkler irrigation systems. Drip irrigation systems are expensive because of their requirements of large quantities of piping and filtration equipment to clean and water. However, the cost of drip irrigation systems varies considerably depending on the crop and terrain. Steep terrain may require several pressure regulators in the system. In many situations the benefits of the drip system will usually overweight the cost of the system, when compared to other methods of irrigation. Selecting widely spaced crops of high market value is necessary to increase the benefit cost ratio in drip irrigation. Under average field conditions, the major components of the total cost of the system lie in the number of laterals/and emitters of the system. Evidently both these items will be low in hards and other widely spaced row crops.