ZIMSEC O Level · Agriculture · Form 3, Form 4
Sources of water
Rivers, dams, boreholes, wells, springs and rainwater harvesting.
Irrigation methods
- Surface/furrow: water flows along furrows; cheap but wasteful.
- Sprinkler: sprays water like rain; suits many crops; costly to run.
- Drip (trickle): delivers water to each plant's roots; most efficient; good for vegetables and orchards.
- Centre pivot: a large rotating sprinkler for big farms.
Advantages of irrigation
Crops can be grown all year, yields are higher and more reliable, and dry regions can be farmed (e.g. sugar cane in the lowveld).
Problems
Salinisation (salt build-up when water evaporates), waterlogging, high costs, and the spread of water-borne diseases such as bilharzia.
Water conservation
Mulching, drip irrigation, irrigating in the cool of the day, rainwater harvesting (tied ridges, tanks), and protecting catchment areas.
Exam tip: When comparing irrigation methods, mention cost, water efficiency and suitability.
Check yourself
- Which irrigation method is most water-efficient?
- Explain salinisation.
- Give two methods of harvesting rainwater on a farm.
Show answers
- Drip irrigation.
- Salts build up in the soil as irrigation water evaporates, harming crops.
- Any two: storage tanks from roofs, tied ridges, small dams, infiltration pits, planting basins.
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