Green Environment Initiatives

What is Subsurface Textile Irrigation?

Subsurface Textile Irrigation (STI), although relatively new, is one of the most water efficient watering methods available. Far superior to surface watering (sprinklers, surface drip etc), it is an enhancement of subsurface drip (SDI) irrigation where water is supplied to the soil from the surface of a geotextile fabric rather than from individual emitters in a drip line.

Dispersing the water over a large area of geotextile reduces the rate of water discharge to the soil bringing it closer to the capillary absorption rate. The geotextile strip also converts the drip line from a series of point sources to a single, broad line source.

Subsurface Textile Irrigation was designed specifically for use underground. Drip lines, designed for use on the soil surface, do not perform well when buried. They produce less uniform wetting patterns and are more sensitive to soil type.

Some important differences between STI and SDI

Design

STI – designed for use under the soil surface

SDI – designed for use on the surface

Emitters

STI – Geotextile behaves as a large, continuous emitter running the full length of the line

SDI – Individual emitters spaced at intervals along the pipe

Wetting Pattern

STI – Produces a wide, continuous and uniform wetting pattern that is elliptical in cross section

SDI – Produces a series of circular wetting patterns that are discontinuous and tear drop shaped in cross section. Soil moisture is less uniform and more water is required to wet up the full root zone.

Recycled Water – Human Health

STI – Safer use of contaminated water because the surface remains dry

SDI – System is more prone to tunnelling which brings water to the surface

Recycled Water – Environmental Health

STI – Risk of contamination of surface and subsurface water with nutrients is lower because water is dispersed over a large volume of soil.

SDI – Water discharge is focussed around each emitter. This saturates the soil and leads to tunneling and deep drainage. The capacity of the soil to absorb nutrients such as phosphorus is also rapidly exceeded leading to early failure of the dispersal area.

Root Intrusion

STI – The physical arrangement of the systems component parts discourages roots growing into emitters

SDI – Herbicide is used to protect emitters from root intrusion in most applications.

When can Subsurface Textile Irrigation be used?

Subsurface Textile Irrigation is suited to most applications where conventional irrigation is used. The main advantage is where water supply is limited, costly or of poor quality. As STI is less wasteful of water than surface irrigation, it may be permitted when strict water restrictions apply.

STI is available throughout the world and has a wide variety of applications including:

· Home lawns and gardens

· Sports turf

· Vineyards

· Broad acre crops

· Green roofs

· Public Parks and Gardens

· Golf courses

· Dog and horse racing tracks

· Tennis courts

· Recycled water projects – commercial or residential
By Geoff Cresswell