The main types of irrigation

Overhead irrigation is commonly used for pasture irrigation, while drip irrigation can be used for feed crops such as maize.

Drip irrigation
Drip irrigation minimises soil erosion and enables the water to be uniformly and accurately controlled
Photo: FW Archive

When water supplies are adequate, irrigation can increase crop yield dramatically. Different irrigation systems are suited to different soils, climates, crops and resources. There are three main types of irrigation systems: surface, overhead and drip (see Table 1).

Table 1

ASPECTSURFACE IRRIGATIONOVERHEAD IRRIGATIONDRIP IRRIGATION
Irrigation WUE55%75%90%
Water quality neededSuitable for water with sediments loads too high for overhead or dripWater quality should be potable to remain safe for people and animalsRecycled, non-potable water can be safely used
SoilNot suited to highly sandy soils with high infiltrationSuited to any soilsSuited to any soils
Water distributionUniform but uncontrolledCan be patchyUniform and controllable
Climate Suited to areas with unlimited water and little windSuited to areas with unlimited water and little windSuited to water-limited areas, where wind may contribute to high evaporation
Preparation and maintenanceLittle know-how required, requires labour intensive field levelling and diggingRequires know-how, little field levelling, maintenance of pipes neededRequires know-how, no field levelling, maintenance of pipes and filtration to prevent clogging needed
Field shapeAny shapeOften determined by sprinkler, e.g. pivotsAny shape
ErosionSoils vulnerable to floods and erosionSoils easily eroded if water poolsSoil erosion minimized
SalinitySoil salinization may occur due to capillary action drawing up salts from below to the wetted soil aboveAs for surface irrigation but salts may be leached out of rooting zone easierSalinity problems may occur at wetting front if system is not flushed periodically
FertilizationNot suited to fertigationSoil can be fertigated but involves nutrient wastageSoil can be fertigated without wastage
Chemicals addedNo limitation on type of fertilizers and biocidesNo limitation on type of fertilizers and biocidesNeed to choose fertilizers and biocides that do not require surface wetting
Crop healthGermination generally not limited by waterGermination generally not limited by waterGermination may be limited water only occurring in the wetted area
DiseasesFoliage remains dry and less susceptible to fungal diseaseFoliage gets wet and encourages disease in some cropsFoliage remains dry and less susceptible to fungal disease
WeedsWeeds get as much water as cropWeeds get as much water as cropWeeds minimized as water targets crop
CostsLowest cost, initially labour intensive.High investment costs, and relatively high labour and energy costs to maintain.Generally has highest investment and replacement costs (plastic degrades in the sun or may be attacked by rodents), but lower labour and energy costs.

 

In a dairy operation, drip irrigation is rarely used, as retrieving the dripper pipes before replanting or reploughing pasture is difficult and costly.However, small-scale dairies, where silage crops such as maize are hand-planted and harvested (as in Kenya), can save water and costs with drip irrigation.

Although expensive to install, sub-surface drip systems reduce the need to retrieve pipes, and may become more common as water becomes scarcer in South Africa.

While having the highest water- and electricity-use efficiency of any type of irrigation system, drip irrigation reduces the cost of cultivation. It limits weed growth to the wetting front, and there is none of the soil erosion associated with flood or sprinkler irrigation.

Source: Hawkins, HJ and Stanway R. 2013. The Sustainable Dairy Handbook: For SA           Dairy Farmers. Nestlé Printers: Bryanston, South Africa