Agricultural Systems in Africa
Senior 3 · Geography
Agricultural Systems in Africa
Lesson 3 of 5
30 min
Fly north along the Nile from Aswan to Cairo and you see a ribbon of green, in places only a few kilometres wide, between two walls of bare desert. Almost no rain falls there, yet the ribbon has fed Egypt for thousands of years and, since the 1820s, has grown some of the finest cotton in the world. The secret is water led from the river onto the land: irrigation.
Figure 3. A section across the lower Nile valley. Every field depends on water brought from the river.
Definition
Irrigation: supplying water to crops by artificial means, from rivers, lakes, dams or wells, where rain is too little or too unreliable. Barrage: a low dam across a river that raises the water level so that it can flow into canals. Alluvium: fertile silt and mud laid down by a river in flood.
| Type | How it works | Example |
|---|---|---|
| Basin (flood) irrigation | Fields are surrounded by earth banks; the river's summer flood fills them, leaves its silt and drains away. One crop a year. | Egypt before the dams of the 1800s and 1900s |
| Perennial irrigation | Dams and barrages store water and release it along canals all year. Two or three crops a year. | Egypt today; the Gezira Scheme, Sudan |
| Furrow (surface) irrigation | Water flows by gravity along small channels between crop rows. | Cotton and vegetables in the Nile valley |
| Sprinkler and centre-pivot | Pumped water is sprayed over the crop; a pivot arm turns in a circle. | Desert farms west of the Nile Delta; large farms in eastern Rwanda |
| Drip irrigation | Pipes drip water onto each plant's roots. Very little is wasted. | Fruit and vegetable farms |
Water can be lifted from a river or well by hand or animal power, with the shaduf (a bucket on a weighted pole), the sakia (a wheel of pots turned by an ox or donkey) or the Archimedean screw, or by diesel, electric and solar pumps.
In Rwanda, irrigation matters most in the dry months. In Season A of 2025, 13.4% of farmers irrigated (12% of small-scale and 64.1% of large-scale farmers), but in Season C, the short dry season from July to September farmed mainly in wetlands and on irrigated sites, 58.9% did (NISR, Seasonal Agricultural Survey 2025).
Definition
Basin irrigation: trapping the annual flood in banked fields. Perennial irrigation: irrigation all year round from water stored behind dams and barrages and led along canals.
Location. The lower Nile valley runs north from Aswan to Cairo, where the river divides and spreads into the Delta before reaching the Mediterranean. Cotton is grown on the valley floor and, above all, in the Delta.
History. Commercial growing began in 1820 with a long-fibred variety found by the French engineer Jumel, under the ruler Muhammad Ali. Output grew fast in the late 1800s as irrigation spread and as the American Civil War (1861–1865) cut supplies of cotton from the USA. Barrages, the Aswan Low Dam (1902) and the Aswan High Dam (completed 1970) turned basin irrigation into perennial irrigation, so a summer crop like cotton could be watered every year.
Favourable factors.
Growing. Cotton is sown in spring, watered along furrows through the summer and picked by hand from September. The raw cotton is ginned to separate the fibre (lint) from the seeds, then baled for spinning or export. The seeds give cooking oil and cattle cake.
Quality. Egyptian cotton is famous for its long fibres, or staple; extra-long staple is 35 mm or longer. Long fibres spin into fine, strong, soft yarn for high-quality cloth.
Definition
Staple: the length of a cotton fibre. Ginning: separating cotton fibre from its seeds.
| Importance of irrigated cotton | Problems | Solutions |
|---|---|---|
| Export earnings and raw material for Egypt's textile industry | Salinisation: with no yearly flood to wash the soil, salts build up | Underground and open drains; careful water use |
| Jobs in farming, ginning, spinning and weaving | Waterlogging where too much water is applied | Drip and sprinkler irrigation; lining canals |
| Cotton-seed oil and cattle cake | The dam traps the silt, so farmers must buy fertiliser | Fertiliser and crop rotation with clover (berseem) |
| Fields can carry two or three crops a year | Bilharzia spreads in slow canal water | Health care, lined canals, clean water supplies |
| Towns and industry grow along the valley | Pests such as the cotton leafworm; competition from food crops and synthetic fibres | Pest control, research into better varieties, guaranteed prices |
South of Egypt, between the Blue and White Niles, lies the Gezira Scheme. Cotton was first tried there in 1904; the Sennar Dam on the Blue Nile, completed in 1925, made large-scale irrigation possible. By 2008 it covered 8,800 km², about half of Sudan's irrigated land, with 4,300 km of canals and ditches. Cotton was its main crop, grown by tenant farmers together with the government and the Sudan Gezira Board.
Worked example
Worked example 1: how much water does a cotton field need? Suppose a crop needs 800 mm of water in a season (illustrative figure). How many cubic metres is that for 1 ha, and for a 5 ha farm?
Worked example
Worked example 2: who irrigates in Rwanda? In Season A of 2025, 12% of small-scale and 64.1% of large-scale farmers irrigated (NISR). Compare them and explain.
Warning
The High Dam ended the Nile flood. Do not write that "the Aswan High Dam floods the fields with silt". It does the opposite: it stores the flood in Lake Nasser and releases water evenly all year. That allows perennial irrigation, but the silt now settles in the lake instead of on the fields.
Tip
When you explain a problem of irrigation, show the cause: "Salinisation, because water evaporates in the heat and leaves its salts in the soil, and there is no longer a yearly flood to wash them out."
British Pathé classroom film from the 1940s: men lifting Nile water with a shaduf. Watch how the counterweight helps, and estimate how much water one man could lift in a day compared with a pump.
Practice
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
