Irrigation methods: surface, sprinkler and drip
How surface, sprinkler and drip irrigation work, their efficiencies, costs and suitability, how to choose, and sprinkler and drip design sums.
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Irrigated land makes up only about a fifth of the world's cultivated area but produces around 40 per cent of its food, and agriculture accounts for roughly 70 per cent of all fresh water withdrawn worldwide. How that water is applied to fields matters enormously: the same crop can be grown with half the water, or lose much of it to runoff, evaporation and deep drainage, depending on the irrigation method and how well it is managed.
Irrigation methods, their efficiencies and their design are core topics in agronomy and agricultural engineering exams.
Surface irrigation
Water is applied at the head of the field and flows over the soil by gravity. It is the oldest and still the most widespread method.
- Basin irrigation: level fields surrounded by bunds are flooded; used for rice, orchards and close-growing crops on level land. Check basins are small basins for row crops and trees.
- Border irrigation: long, gently sloping strips between parallel ridges; used for wheat, fodder and pasture.
- Furrow irrigation: water flows in small channels between ridges of row crops such as maize, cotton, sugarcane and vegetables; only part of the surface is wetted.
- Wild flooding: uncontrolled flooding, inefficient and uneven.
Advantages: low cost and energy, simple, suits many crops. Disadvantages: needs level or uniformly sloping land, high losses from deep percolation and runoff if poorly managed, uneven application, waterlogging and salinity risks. Laser land levelling and surge flow improve efficiency.
Sprinkler irrigation
Water under pressure is sprayed into the air and falls like rain.
- Set systems: portable, solid-set or hand-move laterals with rotating sprinklers.
- Centre pivots, invented by Frank Zybach in the United States around 1950: a lateral rotates around a pivot, irrigating large circles; and linear-move machines.
- Rain guns and travelling big-gun sprinklers.
- Micro-sprinklers for orchards.
Advantages: suits uneven land and sandy soils, controls application rate, allows fertigation and frost protection, and saves labour. Disadvantages: energy for pumping, wind drift and evaporation, wetting of leaves that can increase some diseases, and higher capital cost.
Drip (trickle) and micro-irrigation
Water is delivered slowly, drop by drop, through emitters or drip tape to the root zone of each plant, wetting only a bulb of soil. Modern drip irrigation was commercialised in Israel in the 1960s, building on work by the engineer Simcha Blass.
- Surface drip with emitters on laterals, drip tape for row crops, and subsurface drip buried below the surface.
- Requires filtration to prevent clogging, a pressure regulator, and often a fertiliser injector for fertigation.
Advantages: highest application efficiency, little runoff or deep drainage, dry soil between rows limits weeds, frequent small doses keep soil moisture near optimum, works with saline water better than other methods, and enables precise fertigation. Disadvantages: high capital cost, clogging, damage by rodents and machinery, and salt accumulation at the edge of wetted zones in dry climates.
Comparison and choice
| Factor | Surface | Sprinkler | Drip |
|---|---|---|---|
| Typical application efficiency | 40–70% | 70–85% | 85–95% |
| Capital cost | low | medium to high | high |
| Energy | low (gravity) | high (pressure) | low to medium |
| Land | level or uniform slope | most topography | any |
| Soils | medium to heavy | light to medium | all |
| Crops | most field crops, rice, orchards | field crops, pasture, vegetables | orchards, vegetables, high-value row crops |
| Water quality | tolerant | moderate | needs clean, filtered water |
The choice depends on water supply and cost, energy, soil, topography, crop value, labour and capital. Saving water at field level does not always save water in the basin: if farmers use the saved water to expand irrigated area, total consumption can rise, which is why water policies must consider the whole basin.
Sprinkler and drip design checks
Sprinkler application rate. Sprinklers discharging 1.2 m3 per hour each are spaced 12 m × 12 m.
- Application rate = discharge ÷ area = 1,200 L/h ÷ 144 m2 ≈ 8.3 mm per hour.
- On a soil whose infiltration rate is 6 mm per hour, water would pond and run off, so the designer should use smaller nozzles, wider spacing or a pulsed schedule.
Drip irrigation for a mango orchard. Trees at 5 m × 5 m (25 m2 each), crop water requirement (ETc) 6 mm per day, the canopy shading 60 per cent of the ground, and drip application efficiency 90 per cent:
- Water per tree per day = 6 mm × 25 m2 × 0.60 ÷ 0.90 = 90 ÷ 0.90 = 100 litres.
- With 4 emitters of 8 L/h per tree (32 L/h): operating time = 100 ÷ 32 ≈ 3.1 hours a day.
- For 400 trees (1 ha): 40,000 L per day, or 40 m3.
Surface basin irrigation of the same orchard at 50 per cent efficiency, wetting the whole area, would need 6 × 25 ÷ 0.50 = 300 L per tree per day, three times as much.
Key points
- Surface (basin, border, furrow): low cost, gravity-fed, 40–70 per cent efficient; needs level land and good management.
- Sprinkler (set, centre pivot, rain gun): suits uneven land and sandy soils, 70–85 per cent efficient; needs pressure and energy.
- Drip and micro-irrigation: 85–95 per cent efficient, precise fertigation; high cost, needs filtration.
- Choose by water, energy, soil, slope, crop value, labour and capital.
- Sprinkler application rate = discharge ÷ spacing area, kept below the soil's infiltration rate.
- Field-level savings may not save water at basin scale if irrigated area expands.
What the exams ask
- School-leaving and entrance papers: methods of irrigation with examples, and advantages and disadvantages.
- Degree and research-fellowship entrances: comparison of methods, efficiencies, components of sprinkler and drip systems, fertigation, and selection criteria.
- Agricultural engineering and professional examinations: design calculations for sprinkler and drip systems, pump selection, and water saving at farm and basin scales.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Is drip irrigation always the best choice?
No. It is most valuable for high-value crops, scarce or costly water, and difficult soils. For rice or low-value field crops with plentiful water, well-managed surface irrigation can be more economic.
Why do drip emitters clog?
Suspended sand and silt, algae and bacteria, and chemical precipitates such as calcium carbonate and iron. Good filtration, flushing laterals and periodic acid or chlorine treatment prevent clogging.
Can sprinklers spread disease?
Wetting leaves can favour some foliar diseases. Irrigating early in the day so leaves dry quickly, or using drip for susceptible crops, reduces the risk.
Sources
- FAO. AQUASTAT: FAO's Global Information System on Water and Agriculture. FAO, online.
- Brouwer, C., Prins, K. and Heibloem, M. Irrigation Water Management: Irrigation Scheduling, Training Manual 4; and Irrigation Methods, Training Manual 5. FAO, 1988–1989.
- Keller, J. and Bliesner, R. D. Sprinkle and Trickle Irrigation. Van Nostrand Reinhold, 1990.
- Michael, A. M. Irrigation: Theory and Practice, 2nd edition. Vikas Publishing, 2008.
- Perry, C., Steduto, P. and Karajeh, F. Does Improved Irrigation Technology Save Water? A Review of the Evidence. FAO, Cairo, 2017.
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