DRIP, DRIP, DRIP

IS drip irrigation REALLY worthwhile to keep our personal patches of green alive and healthy?

WELL. In theory, yes. In practical terms…………..it depends.

The concept of drip irrigation is rather simple – plants are irrigated when water is allowed to drip out of holes in a pipe, usually located near its roots.  Drip irrigation systems can be located at the surface, or under the top soil (the subsurface) and thus directly in the root zone.  Applications with drip irrigation water are usually more frequent than other methods and thus provide a favourable high moisture level in soils for our vegetables, flowers and trees. A typical system consists of the following major components:

  • Pump unit – to take water from the source and provide pressure for delivery into the pipeline
  • Control head – controls the discharge and pressure, may include filters
  • Main and submain lines and laterals – supply water from from the control head into the garden/field
  • Emitters or drippers – devices used to control the discharge of water from the pipes to the plants.

These kinds of systems are typically used in hot and dry climates where water is rather precious, and can be installed on a larger agricultural scale, or smaller domestic scale. While primitive drip irrigation systems are thought to have first been used in China in the first century through buried clay pots filled with water, the use of plastic to hold and distribute water relatively evenly was developed in Australia by Hannis Thill after World War II.  This system was further refined in Israel by Simcha Blass in the mid 1960s when the first practical surface drip irrigation emitter was born, allowing agriculture to flourish in Israel’s Negev Desert (a place of extremely limited rainfall) and expand to other arid parts of the world.

The results of drip irrigation in the Negev Desert (Source: http://i.bnet.com/blogs/iz2.jpg)

The results of drip irrigation in the Negev Desert (Source: http://nihs.nl/2013/01/24/israel-in-perspectief/)

Given the kinds of historical sprouting success that has been associated with drip irrigation over the last 50 years and longer, the advantages of this system over more traditional sprinkler methods seem obvious when applied to a more local garden level:

  • Increased water application efficiency (and reduction in evaporation)
  • Uniform water distribution
  • Maintenance of soil moisture at the root zone
  • Prevents leaching, water run-off and soil erosion
  • Accommodation of gardens with irregular shapes/heights
  • Foliage remains dry, minimising sunburn and risk of disease
  • Safe use of recycled non-potable water

However, depending on the conditions of a garden, the way it’s installed and the material from which the pipes are made, these systems can really be a big ‘drip’ on your green patch. In particular, headaches may arise due to:

  • Expense – initial costs can be more than overhead systems
  • Clogging – if water is not filtered and equipment is not properly maintained
  • Difficulty in using over large areas of turf and if it requires maintenance, will have to be dug up
  • Waste of time, water and plants if not installed and maintained properly (due to lack of consideration of topography, soils, dripper spacing and plant and germination requirements)
  • Salinity and leaching – as drip irrigation is designed to minimise leaching, if water of high salinity or alkalinity is used for irrigation and there is not enough rain to leach the soil, salts may build up in the root zone causing the soil to gradually become unsuitable for cultivation (granted this is unlikely to happen if you use scheme water, and there is more risk on larger scale areas)
  • HOLES – if pipes get hole-y as a result of sun or pest damage, you often won’t find out until you’ve lost a beloved shrub and it can be time-consuming to determine exactly where the break(s) are located

However, a lot of these issues can be resolved with due consideration and care; by ensuring that protective sleeves, filters and protective layers of soil and mulch are part of your system, that dripper intervals are located according to the root zone of different sized plants, the soil conditions (considering high infiltration rates in sand versus ponding in clay) and topography of your garden, through regular maintenance by flushing of pipelines, and through appropriate irrigation timing (shorter but more frequent watering periods).

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In addition, new designs in drip irrigation systems are addressing some of these issues and making installation and maintenance much easier. A recent example of this is the use of rigid PVC lateral lines and risers buried just under the top soil, from which the outlet for multiple drip emitters may be connected.  Compared to polypipe or Netafim installations, materials such as these are better protected as a result of their position under topsoil or mulch, and thus less prone to damage from exposure to weather, pests. Distribution tubing is also not so easily dislodged and herbicides are not required once the system has been flushed and emitter heads installed,due to the strength and integrity of the system. This example is just one of many designs which are being developed to improve the useability of drip irrigation.

In summary, drip irrigation systems in rain-starved cities such as Perth are definitely worthwhile for use in domestic gardens IF installed correctly with consideration to site conditions, layout, emitter position and intervals, and the types of plants which require watering. They also provide an opportunity to use recycled non-potable water in subsurface systems, which will be increasingly advantageous, given the drying climate we have all come to know too well, the increasing price of water associated with infrastructure and energy intense water supply systems such as desalination plants, and the ever-increasing water constraints such as Water Corporation’s winter sprinkler bans which applies to both scheme and bore water and controlled watering days over summer. If drip irrigation systems were installed by all Perth residents in the appropriate locations of their garden, it would go a long way to reducing Perth’s overall domestic irrigation water demand. And imagine if all local governments used it in their parks too!

To get more advice on drip irrigation systems, organisations such as Gardening Australia, the Water Corporation, and Irrigation Australia are good places to obtain some solid information, set up your own system and get your flowers blooming without throwing buckets of water at them!

 

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