Choosing an irrigation system for your crop is a key consideration in any commercial farming venture. The right system guarantees high yield, efficiency, environmental preservation, and profitability.
Many smallholder farmers in Kenya still use the ancient furrow irrigation system, which though cheap is water wasteful, laborious, and heavily leaches the soil, which in turn significantly limits crop yield. Below, we look at key considerations when choosing a system:
1. Budget
Drip irrigation systems and the centre pivot system are expensive to install. However, drip irrigation systems conserve 70 per cent of the water equivalent used by centre pivot systems and overhead sprinklers. A drip irrigation system too will be powered by gravity, cutting energy costs.
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A grower must choose the right drip pipe thickness according to the crop location. In the open field, 0.4mm thickness is advised.
This is because the drip tape will be exposed to direct radiation from the sun, and will also be disturbed often during farm activities such as; weeding and tilling.
For the greenhouse, 0.2 or 0.3mm will do because the drip tape is not exposed to direct radiation, and soil management activities are minimal.
Overhead irrigation is more affordable at the point of installation but has an energy recurring cost because a water pump must be used to power the system. Its water use is inefficient and sometimes wasteful.
Cost of irrigation per acre
i. Drip irrigation
- 3 drip lines per bed for onion, garlic, strawberry, and herbs. From Sh145,000
-2 drip lines per acre for tomato, peppers, brassicas (cabbage, lettuce, spinach, kales, broccoli, and cauliflower). From Sh25,000
-1 drip line per bed for watermelon, pineapple, and butternut. From Sh80,000
-Button drippers or online drippers for fruits. From Sh45,000. This one varies considerably depending on the fruit tree orchards or forestry trees spacing
ii. Overhead irrigation
Pop-up sprinklers. These are sub-surface sprinklers which as the name suggests ‘pop-up’ above the surface only when irrigating. These are used only in lawns, ornamental gardens, and stadiums, and are they are the most expensive sprinkler type to install. The cost is Sh150,000.
-Rain gun, Meganet, or Impact sprinklers. From Sh50,000
-Rain hose kit. From Sh55,000
Sprinklers and the rain hose kit are also used to irrigate in fruit tree orchards or in commercial forestry production.
2. Crop type
· Solanaceous crops such as; tomato, pepper, potato, brinjals, eggplant, and other Asian vegetables are highly susceptible to fungal infections when the leaves are wet leaves. The same problem exists for export green beans. The solution is to use a drip irrigation system for these type of crops because it leaves no moisture on the leaves.
· Onion, garlic, maize, leafy vegetables such as brassicas do well with both overhead irrigation and drip irrigation. Overhead irrigation will be either through sprinklers or the rain hose irrigation kit. In the hot months when diamond black moth (on brassicas) and aphid pest attacks occur, overhead irrigation controls these pests.
· Tree crops will use overhead or button drip irrigation
· Carrot, coriander, and African traditional vegetables. Use the rain hose kit in such densely spaced crops
· Lawn grass. Install pop-up sprinklers.
3. Crop acreage
Large plantation acreage is irrigated overhead using the centre pivot system, or through drip irrigation. Rain hose kits and overhead sprinklers are used on smaller acreages.
4. Stage of growth
· Nurseries. Irrigation for any tree or vegetable nurseries is done by overhead irrigation through sprinklers or a rain hose kit. This is because the area under irrigation is limited and the seedlings are closely spaced.
· Mature crops will work with the other options based on crop type.
5. Water availability
· Overhead irrigation. The use of sprinkler irrigation systems, centre pivots, or rain hose kits. To use these, there must be a permanent, and plentiful source of water.
· Drip irrigation kit. This is ideal when there is a need to conserve water. For example, if the water source is seasonal or shared by the community or in an arid and semi-arid area.
6. Land topography
While sprinkler and rain hose systems are easy to use on flat or gently sloping terrain, it is more difficult on steep sloping land. This is because steep slopes have low water percolation, so the risk of run-off is high.
Here, a drip system should be used; pre-perforated drip tapes for vegetables and pressure compensated button drippers for fruit or forestry trees. Pressure compensated button drippers ensure that each tree receives an equal amount of water for even growth.
7. Growing method
When growing in a greenhouse, the farmer is restricted to use drip irrigation. If it is an open field crop, then the grower will choose from any of the given irrigation methods.
[Wamae Mwangi is a director at Grekkon Limited – Irrigation Hub]
