Flooding irrigation is a practice where water is pumped or allowed to flow into channels passing between crop rows in areas where farmers have level fields. This flooding system is an effective method of managing weeds and pests, preventing the completion of their lifecycles as they are either drowned or isolated from air and sunlight. This practice is applicable in areas where there are favourable climatic conditions with high rainfall amounts; and is not recommended in arid and semi-arid environments. Flooding is controlled using water pumps in order to reduce waterlogging problems, and fields should not be entirely flooded, with surges of periodic flooding used to distribute water and avoid wastage to run-off, evaporation and creation of anaerobic conditions in the soil. Flood waters can be filtered using a fine mesh to control pests and diseases from spreading to neighbouring fields. Sandy soil is not favourable for flood irrigation as it does not evenly distribute water across the field whereas loam and clay soils distribute water efficiently across the field.
It is considered a climate smart practice because it requires less energy, and can promote crop productivity, whilst controlling weeds and pests.
To effectively leverage flooding irrigation:
- Step 1: prepare the field, digging parallel furrows and raising beds with the excess soil. Crops are planted in beds, and the irrigation water will flow in the furrows.
- Step 2: Using a pump or gravity fed water storage, allow water to flow into the field, flooding furrows.
- Step 3: Insert a fine mesh or introduce a hessian sack at the in-flow point to trap weeds and pests.
- Step 4: Water release should be moderated so as not to flow too fast and erode beds, and too slow such that it remains trapped at the in-flow point.
- Step 5: Water release can be more effective if released in surges, taking advantage of infiltration rates and capillary action in soil.
- Step 6: Observe progress. Avoid leaving soil crusts, which will make water rush over.
A sustainable water source must be identified and a pumping/irrigation system should be used.
- The Food and Agriculture Organisation (FAO), 1989. Guidelines for designing and evaluating surface irrigation systems. Rome, Italy.
- The Food and Agriculture Organisation (FAO), 1985. Irrigation Water Management: Irrigation Methods. Rome, Italy.
- FAO 2014. Irrigation Techniques for Small-scale Farmers: Key Practices for DRR Implementers. Rome, Italy.
- Kerr B. 2016. Getting flood irrigation right. Farmer’s Weekly.
- African Farming 2018. Saving water: flood irrigation explained. African Farming.com
Benefits
- A flood irrigation system reduces weed growth and acts as preventive measure against spread of pests and diseases.
- Requires less energy, so reduces costs. Gravity does the work, so less need for pumping.
- Flood irrigation can work with lower-quality water because the water doesn’t contact with crop leaves, which is usually a concern with waste water.
Drawbacks
- Requires larger amounts of water than other types of irrigation – only suitable in wetter climates.
- Is considered more labour intensive as land must be closely managed, and prepared.
- Land must be level, or manually/mechanically levelled.
- Cannot effectively operate in sandy soils.
- Very clay-heavy soil can easily become water-logged.
- If not managed properly, can be very wasteful with respect to water.
