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Irrigation made easy – Part 16: Mini-sprinklers and garden sprayers

Thousands of people all over Africa rely on community gardens to provide them with food and an income. Community gardens constantly gain in importance in poor rural communities.

Irrigation plots are small, and it is often difficult to plan appropriate systems using conventional irrigation technology. Some of the equipment used to irrigate small areas in community gardens were developed for the urban garden.

Irrigation systems developed specifically for small garden plots include hand-watering systems, bucket-drip systems, and short-furrow flood irrigation systems using portable hoses. Pressurised garden systems use mini-sprinklers and garden sprayers to distribute water. Garden sprayer systems differ from more conventional sprinkler systems.

Garden sprayers typically cover a small area.

The systems are labour intensive, and farmers will spend much time moving sprayers. Garden sprayers work at low pressure (between 150 and 200 kPa). Small sprayers tend to spray water up against tall crops, and water will not be spread over the plot.

Garden sprayers typically cover a small area. The spay radius will seldom exceed 6 metres. Application rates are often very high and if the sprayer is left in one position for too long, water will run off and not infiltrate into the soil.

Garden sprayer systems differ from more conventional sprinkler systems. The systems are labour intensive and farmers will spend much
of the day moving sprayers.

These systems are normally designed so that the emitter (sprayer) is moved every 5 to 10 minutes. The ‘farmer’ stays in the field the whole time and constantly moves emitters.

Small orifice sprayers

This type of sprayer is the most likely choice for a small garden system. Water is forced into a swirling vortex and escapes through an orifice to wet an area of 7 to 8 m in diameter. A wide selection of orifice sprayers is available. Sprayers range from simple cast metal units to more elaborate plastic sprayers.

The distribution pattern of orifice sprayers is irregular. More water is sprayed to one side.

The distribution pattern of orifice sprayers is irregular. More water is sprayed to one side. This makes it important to always point the sprayer in the same direction when using the sprayer in the field. The system design will attempt to overlap the natural skewed distribution pattern to achieve an even distribution. If sprayers are not properly aligned, the application rate will be erratic and irrigation efficiency will be reduced.

Good vegetable production is possible in small community garden plots that use garden sprayers to irrigate.

Orifice sprayers are closely spaced, with normal in-field spacing of between 5 and 6 metres. A single sprayer can be used to irrigate an area of up to 600 m2, or a number of garden beds.

Care should be taken to allow for the effect of friction in supply hoses when designing or operating these systems.

Sprayers normally connect to a supply line by means of a garden hose attached to a riser valve. Care should be taken to allow for the effect of friction in supply hoses when designing or operating these systems.

Sprayers normally connect to a supply line by means of a garden hose attached to a riser valve.
A single sprayer can be used to
irrigate an area of up to 600 m2, or a number of garden beds.

Good vegetable production is possible in small community garden plots irrigated with sprayers.

This series is published with acknowledgement to the ARC Agricultural Engineering for the use of their manuals. Visit www.arc.agric.za for more information.

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