Drip irrigation

Drip irrigation is a type of micro-irrigation system that has the potential to save water and nutrients by allowing water to drip slowly to the roots of plants, either from above the soil surface or buried below the surface. The goal is to place water directly into the root zone and minimize evaporation. Drip irrigation systems distribute water through a network of valves, pipes, tubing, and emitters. Depending on how well designed, installed, maintained, and operated it is, a drip irrigation system can be more efficient than other types of irrigation systems, such as surface irrigation or sprinkler irrigation.

Components and operation:

Components used in drip irrigation (listed in order from water source) include:

  • Pump or pressurized water source
  • Water filter (s) or filtration systems: sand separator, Fertigation systems and chemigation equipment.
  • Backwash controller
  • Pressure control valve
  • Distribution lines (main larger diameter pipe, maybe secondary smaller, pipe fittings)
  • Hand-operated, electronic, or hydraulic control valves and safety valves
  • Smaller diameter polyethylene tube (often called “laterals”)
  • Poly fittings and accessories (to make connections)
  • Emitting devices at plants (emitter or dripper, micro spray head, inline dripper or inline drip tube)

In drip irrigation systems, pump and valves may be manually or automatically operated by a controller.

Most large drip irrigation systems employ some type of filter to prevent clogging of the small emitter flow path by small waterborne particles. New technologies are now being offered that minimize clogging. Some residential systems are installed without additional filters since potable water is already filtered at the water treatment plant. Virtually all drip irrigation equipment manufacturers recommend that filters be employed and generally will not honour warranties unless this is done. Last line filters just before the final delivery pipe are strongly recommended in addition to any other filtration system due to fine particle settlement and accidental insertion of particles in the intermediate lines.

Drip and subsurface drip irrigation is used almost exclusively when using recycled municipal wastewater. Regulations typically do not permit spraying water through the air that has not been fully treated to potable water standards.

Because of the way the water is applied in a drip system, traditional surface applications of timed-release fertilizer are sometimes ineffective, so drip systems often mix liquid fertilizer with the irrigation water. This is called fertigation; fertigation and chemigation (application of pesticides and other chemicals to periodically clean out the system, such as chlorine use chemical injectors such as diaphragm pump, piston pumps, or aspirators. The chemicals may be added constantly whenever the system is irrigating or at intervals. Fertilizer savings of up to 95% are being reported from recent university field tests using drip fertigation and slow water delivery as compared to timed-release and irrigation by micro spray heads.

Properly designed, installed, and managed, drip irrigation may help achieve water conservation by reducing evaporation and deep drainage when compared to other types of irrigation such as flood or overhead sprinklers since water can be more precisely applied to the plant roots. In addition, drip can eliminate many diseases that are spread through water contact with the foliage. Finally, in regions where water supplies are severely limited, there may be no actual water savings, but rather simply an increase in production while using the same amount of water as before. In very arid regions or on sandy soils, the preferred method is to apply the irrigation water as slowly as possible.

Pulsed irrigation is sometimes used to decrease the amount of water delivered to the plant at any one time, thus reducing runoff or deep percolation. Pulsed systems are typically expensive and require extensive maintenance. Therefore, the latest efforts by emitter manufacturers are focused on developing new technologies that deliver irrigation water at ultra-low flow rates, i.e. less than 1.0 L (2.1 US pints; 1.8 imperial pints) per hour. Slow-and-even delivery further improves water use efficiency without incurring the expense and complexity of pulsed delivery equipment.

An emitting pipe is a type of drip irrigation tubing with emitters pre-installed at the factory with specific distance and flow per hour as per crop distance.

An emitter restricts water flow passage through it, thus creating head loss required (to the extent of atmospheric pressure) to emit water in the form of droplets. This head loss is achieved by friction/turbulence within the emitter.

Advantages:

The advantages of drip irrigation are:

  • Fertilizer and nutrient loss is minimized due to a localized application and reduced leaching.
  • Water application efficiency is high if managed correctly.
  • Field levelling is not necessary.
  • Fields with irregular shapes are easily accommodated.
  • Recycled non-potable water can be safely used.
  • Moisture within the root zone can be maintained at field capacity.
  • Soil type plays a less important role in the frequency of irrigation.
  • Soil erosion is lessened.
  • Weed growth is lessened.
  • Water distribution is highly uniform, controlled by the output of each nozzle.
  • Labour cost is less than other irrigation methods.
  • Variation in supply can be regulated by regulating the valves and drippers.
  • Fertigation can easily be included with minimal waste of fertilizers.
  • Foliage remains dry, reducing the risk of disease.
  • Usually operated at lower pressure than other types of pressurized irrigation, reducing energy costs.