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The border area of Mauritania and Senegal in westernmost Africa is an example of both expanding irrigation and desertification. The international border between Mauritania and Senegal is the Senegal River, flowing westward and interrupting the arid lands to the north and south. The regional capital of southwestern Mauritania is Rosso, which is on the north bank of the river, and the town of Richard Toll ("Richard's Field" in the Wolof language) is on the south bank. The effects of Mauritania's National Highway 2, which connects the regional capital Rosso to the national capital Nouakchott, on the desert is seen in the close-up images.

Map of the featured area.

The word desertification, if split into its roots, logically would mean the event of non-desert land becoming desert, but it is not quite so simple. Desertification is usually defined as a process that happens to land that is already normally arid (dry) or semiarid and it's not just caused by drought. In fact, the crucial factor is a decline in the biological productivity of the land—the amount of vegetation that grows (either naturally or that people have planted)—as well as the animal life supported by the plants. If desertification continues, eventually the land becomes a desert, with increased wind and water erosion, decreased soil fertility, and decreased water-retention capacity. Plant and animal communities decline in number and diversity, as many species can no longer survive.

Desertification is usually a patchy development, spreading outward from pockets of land where the vegetative cover has been harmed or destroyed, so that sandy dry soil begins to drift and vegetation is unable to reestablish itself.

In western Africa, boreholes (water wells) are often the points of this vegetation disturbance, because they attract livestock, which overgraze the land nearby. But in this example, the point of disturbance is a paved highway that was built to connect Nouakchott, the national capital of Mauritania, with the regional capital Rosso. Besides travel and transportation, the highway also encourages building and settlement. All of these activities consume vegetation for grazing, fuel, and building material. The vegetative cover becomes disturbed, some sandy soil begins to drift, and the process of desertification is underway.

In these images, the disturbances the highway causes become evident. The 1972 image shows the highway slicing across the desert's sand dunes. The other images show a widened corridor, the brighter tones that follow the highway.

There has been irrigation along the Senegal River in the Richard Toll, Senegal, area since the 1940s. With little dissolved salt, the quality of water in the Senegal River is generally good for irrigation. However, proper drainage and cropping schedules are needed to keep levels of alkaline content from accumulating in the root zone.

In the 2011 image, many bright red fields can be seen. Most of them are sugarcane and rice, and virtually all of them are irrigated. The amount of irrigated land increased greatly between 1972 and 2011, and new irrigation canals are visible. The irrigated crops are able to grow in the dry season because they are not dependent on rainfall.

On the Mauritania side of the river, growth in agriculture is limited by poor soil quality and lack of agricultural education. Most of the country's food is imported. Since almost half of Mauritania's population lives at or below the national poverty level, the imported food is not always affordable. In 2007, the people's distress was expressed by food riots.

In the 2011–2012 growing season, the Mauritanian government began some new strategies to increase the yield and amount of crops grown. By training young farmers about agriculture, investing money into more irrigation, and introducing genetically modified crops that can survive in Mauritanian conditions, leaders of the country are hopeful that better times are to come for farming.

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