Drip Irrigation in Landscaping
Drip irrigation - the bottom-line
Drip irrigation can save up to 90% on water consumption in a garden.
The entire area under drip gets the same amount of water per square area, ensuring even plant growth throughout.
It is not influenced by plant growth above ground therefore no alterations are required when plants get bigger and obstructive.
The system is self sufficient and self-cleaning resulting in much less maintenance.
A drip system can be installed in such a way that it is 100% vandal-proof without affecting the performance in any way.
This type of system is the only one that offers the user total control over the actual plant needs and the elements.
Drip irrigation was developed in Israel in 1965 and is used extensively today in more than 80 countries around the world. The present generation of inline drip components made their debut in 1978.
The main reasons for developing drip irrigation in Israel were limited available water sources and harsh conditions under which it had to be implemented.
Water suitable for watering crops has always been scarce and very expensive, therefore farmers had to utilise the available water "to the last drop".
Added to the lack of water was the fact that the climate was very harsh, with temperatures in the southern desert regions occasionally exceeding 50 ºC during summer. Taking these factors in consideration it would have seemed like an impossible task to develop suitable means to water crops.
However, through dedication and continuous development these problems were overcome and in the process an extremely efficient watering system was developed.
Although a very precise science, the principles of drip irrigation are fairly simple. Water moves through the soil by means of capillary action, which is the radial movement (outward and upward) of water through the soil that fills the spaces between particles with capillary moisture.
Capillary moisture is the water that is held in pore spaces by the surface tension between the water and soil particles. This is the primary source of water for plants and is also referred to as "available moisture".
There is a misconception that water only moves downward through the soil, pulled by gravity. In fact when water is applied slowly, as is the case in drip irrigation, water radiates outward from its source point, creating an overlapping wetting pattern beneath the surface.
In most soil types, ranging between heavy clay soils and sandy types, a sub-surface drip irrigation system penetrates the soil much better than overhead surface type systems. Heavy clay and sandy soils are a mixture of sand, silt and clay.
Loam, which contains equal proportions of sand, silt and clay, is ideal. However, plants can thrive in a very broad spectrum of soil textures when subsurface watering is applied at the proper rate, with appropriate spacing.
The comparisons between drip and conventional irrigation should be made in terms of:
Rate of application of water.
Initial installation cost.
Efficiency of the system.
Period of time to capitalise it.
A drip irrigation system will normally cover a bigger area than sprinklers, using the same amount of water. The major difference between the two types of installations is the percentage of water being utilised by the plants that are irrigated.
Losses to evaporation in a conventional system are considerable. During the hot months this can range anywhere between 50% and 95%, with the result that water evaporates faster than it can penetrate the soil. The denser the soil type, the more severe the losses.
A properly designed drip system can eliminate evaporation losses from the soil surface, depending on the actual installation and the effectiveness of surface mulching, etc. that is used. Although a drip system may cost more to install than a normal system initially, it will capitalise itself soon when running costs are considered.
Once a drip system is installed correctly and running, maintenance is very low as it is self-cleaning and flushes itself out automatically before and after each running cycle.
With a drip system it is possible to achieve totally uniform water coverage over an area being watered. When spaced correctly the same amount of water is applied per square metre throughout.
The system is also "pressure compensating" and at a pressure of between 0.5 to 4-bar, it will distribute exactly the same amount of water over the area being irrigated. Because drip lines are either sub-surface or positioned on the ground, water penetrates the soil directly.
When water becomes airborne (as with a normal system) the water particles drift and much of it falls in areas where it was not intended (like pathways, patios, against windows, etc.) and this problem is further compounded in windy conditions.
Water comes out of a sprinkler nozzle at high pressure and this causes the water to atomise and break up into very fine particles, which are too light to fall to the ground immediately and much of it evaporates long before it gets near the ground.
Drip lines are particularly useful in hard-to-water areas, for example where the space is too narrow to be watered with conventional sprays. Conventional sprays cover a minimum radius and when placed in an area which is too narrow for the "throw" distance, it results in over spray into areas that should not be watered.
A good example is traffic islands. With conventional methods of irrigation, a very high percentage of the water usually ends up running down the road. The reasons for these losses are wrong "throw" distances, wind or both.
A major problem associated with sprinklers in landscaping applications is obstructions by plants.
When the original installation takes place it is done in such a way that optimum coverage of an area can be obtained. However, no allowance is made for plant growth. What normally happens is that plants thrive in the initial period and significant growth is attained until the plant gets bigger and denser.
At this point the sprinkler cannot maintain the original spray pattern resulting in some parts being over watered and other parts being left completely dry because the water cannot penetrate the growth.
This often results in losses of plants. Instead drip lines can be laid flat on the ground surface where the water enters the soil directly and the watering pattern is not influenced by plant growth above the ground. This type of installation is especially useful when the growth is very dense (and would use less than a third of the water as well).
Most of the sprinklers available in South Africa are manufactured in the United States. The use of these devices is strictly regulated in the United States in an attempt to conserve water and stay within allocated of water quotas.
In South Africa, water consumption for landscaping purposes is almost totally unregulated, except for the occasional water restrictions in major metropolitan areas. Although the landscape irrigation industry claims that the principles of water conservation are followed with sprinklers, it is blatantly ignored in practice when these installations take place. In the greater Cape Town area there are thousands of examples of uncontrolled wastage.
These systems cannot operate in sandy conditions.
Drip irrigation was developed in Israel, with vast regions consisting of desert sand. For a system to run properly, the water retention capabilities of the soil needs to be determined to calculate the spacing of drip lines. This also impacts on the effectiveness of the installation and eventual material cost.
The drippers get blocked with sand.
Factors which cause blockages are the absence of correct filtration; line-flush valves and/or vacuum breakers. If there is no filter sand can enter the installation from the source, causing blockage.
If an installation is sub-surface and set at a gradient, the presence of a vacuum breaker is crucial. If it is absent, the water will try to suck in sand from outside because gravity pulls the resident water in the lines downwards when the cycle ends. The absence of these components will eventually destroy the drip devices.
Roots grow into the sub-surface drippers.
This can happen when the soil is frequently allowed to dry out too much and results in roots penetrating the pipes in search of water. Correct scheduling will prevent this problem, but if the plant is a particularly vigorous grower like Kikuyu, a filter with Treflan-impregnated disc elements (a selective herbicide) can be introduced periodically.
This chemical (as well as liquid fertilisers) can also be fed into the installation by means of a fertiliser injector, which works on the principle of a venturi. Instead of killing the plant, the Treflan creates a "bio barrier", which discourages root growth in that desired area.
Landscaping applications for drip are very limited
Contrary to popular belief, the applications for drip irrigation are much more universal than sprinklers. With very few exceptions, areas where sprinklers cannot be used can be serviced with drip irrigation, while areas traditionally watered with sprinklers can also be placed under drip irrigation.
How does drip irrigation interact with landscaping?
The final results obtained with this method of irrigation are influenced to a great extent by the quality of the landscaping.
Growth of plants is proportional to the amount of nutrients in the soil. Drip lines provide basic water to plants and releases the nutrients to the plants. Poorly prepared soil normally results in the plant surviving with slower or stunted growth.
To obtain the best results, the landscaper has to carefully consider the method of irrigation to be used. This can be done very simply with drip irrigation, with just a little bit of planning and a slight change of planting habits and techniques. Young plants do best when planted in close proximity to the dripper, and the position of the inline drippers is easily identifiable by the position of the manufacturer's stamp in the area where the water is emitted.
In some landscapes mist sprayers can sometimes be added to the drip lines to allow small plants to establish. Once the root systems of the plants are established enough, the sprayers may be removed from the line.
Large patches of annuals may require that the mist sprayers be kept there permanently, without affecting the rest of the planted areas. Identifying the exact requirements of the site to be irrigated is crucial to the success of any drip installation. External factors such as sun hours; soil temperature and texture; degree of shelter from the wind; size and needs of mature plants; pests, etc. need to be considered.
Retrofitting drip into existing installations
It is usually possible, almost without exception, to convert existing sprinkler installations to a drip type installation. This is a cost-effective method provided the existing infrastructure of the irrigation is properly functional.
Existing supply lines may be used because it is usually the identical area that gets converted and almost always the primary installation will be simplified. Considering that an area approximately three times the size of that covered with conventional sprinklers can be irrigated with a drip installation, you may end up with a two-station installation instead of the original six- station installation.
Information supplied by Philip Botha of Cape Waterplant. For more information contact , or www.capewaterplant.co.za or telephone 021 551 1911.