Maize, Africa’s New World Crop

While the Americas produce more of their native crop in total volume, the overall impact of maize globally may be greatest in Africa, where its expansion as a major food source has paralleled the continent's economic and nutritional crises.

Since its first arrival with missionaries, merchants and slave traders, the crop has expanded its domain rapidly. In the past two decades, rapid advance of maize as a major food crop in Africa has caught the imaginations of agricultural economists and — international policy planners. They see this as an agricultural sea change that could rival Asia's Green Revolution of the 1970s.

Entrepreneurial economists see the dominance of maize in Zimbabwe, Kenya, Malawi and South Africa as a free-market economic miracle.

The story of African maize tells us a great deal about the continent's distinctive physical and cultural environments. Despite Africa's enormous diversity of cultures, ecologies and aesthetic sensibilities, in recent years Africans have seemingly reached a consensus that maize is their favorite food and that its color should be white — not yellow, red or blue.

At the end of the 20th century, the world planted 140 million hectares of maize each year. Of that total, 96 million hectares were in developing countries, a category that includes all of sub-Saharan Africa. Although 68% of all land planted with maize is in the developing world, it accounts for only 46% of the world's 600 million tons of production as of 1999.

The discrepancy reflects the fact that the average maize yield in industrialized countries is eight tons per hectare, but in the developing world less than three.

Although maize arrived in Africa 500 years ago, it is nevertheless a relative newcomer in a very old and complex environmental setting.

Africa is the oldest continent in human terms, but if we go even further back, in geological terms it was the largest fragment of what was the original geological landmass, Gondwanaland.

The soils and geomorphology of Africa show both its age and also recent episodes of volcanic upheavals, deposition of sediments and the action of water and wind on the land's surface.

In altitude, the extremes range from 120 meters below sea level in the Danakil depression near the Red Sea to 5,895 meters above sea level at the peak of Mount Kilimanjaro.

In northeast Africa, the geological domes that extended from Ethiopia to Tanzania split open 750,000 years ago to create the Great Rift Valley. The Great Lakes formed when the Eastern Rift Dome lifted the earth's crust and left behind a series of long, deep lake basins stretching from south of the equator to, and including, the Red Sea itself.

The highlands of northeast Africa form what biologist Jonathan Kingdon calls a fractured dome. While only a small fraction of Africa's landmass lies above 1,500 meters — half of those highlands are in the region of Ethiopia and Eritrea — a concentration that gives the continent as a whole a tilt from northeast to southwest.

Forty percent of Africa's land has a slope of more than eight degrees, resulting in the movement and redesposition of soil by rain and river systems — erosion. Erosion is not so much a recent crisis as a consistent and inexorable historical process that defines the areas where maize has found an accommodating ecological niche.

Viewed from a satellite, the continent's major features are vast alluvial plains broken by the branching of old streambeds and living rivers.

At ground level the textures and hues of the different soils are more visible. Africa's soils vary dramatically in color, chemistry and structure, ranging from light, sandy arenosols to heavy, poorly drained black "cotton" soils (vertisols).

That something over a quarter of the continent's tropical soils are acidic is significant, since for farmers these soils pose special problems. Not only are acidic deficient in phosphorous, calcium and magnesium, they often contain toxic levels of aluminum.

Even more common in Africa are the red porous laterite soils, which are liable to lose nutrients and are low in nitrogen and phosphorus — both critical to maize plants' yield. These soil conditions are all local phenomena that allow us to make few generalizations.

Such variations, though they are a nightmare for modern industrial agriculture, which seeks uniformity and economics of scale, have encouraged African farmers to practice agriculture as a craft rather than an industry.

Historically, African farmers have dealt with the variation by creating patchwork plots that reflect soil and crop types — that is, by matching crops to soils and climate conditions.

The role of maize and the landscapes of Africa reflect the changing patterns of the climate. Unlike in temperate zones, where growing seasons and life cycles respond most directly to fluctuations in temperature, in Africa the rhythms of life reflect primarily the availability of moisture, especially rainfall.

Africa's annual patterns of rainy and dry seasons, humidity, soil moisture and length of growing season result from the yearly rhythms of global cyclonic winds, ocean temperatures and the earth's rotations around the sun.

In following the tilt of half the earth toward the sun in summer and away in winter, the trade and anticyclonic winds set the yearly cycle of rainy and dry seasons.

This shifting zone of rain-bearing turbulence — which climatologists call the Inter-Tropical Convergence Zone (ITCZ) — sets a bimodal or two-part pattern of seasons, one wet and one dry, which characterizes the continent as a whole.

This seasonality, however, also produces subtle variations from year to year. In certain places, elevation, topography and global climate anomalies such as El Niño (or ENSO), La Niña and tropical Atlantic surface circulation signal drought to the regions of Africa located north of the equator moves from south to north of the equator as the earth tilts toward the sun in the summer months — June to September.

These turbulent movements north of the equator bring summer rains in the northern hemisphere. Africa's annual weather cycle is predictable in broad seasonal terms, even if it is at times erratic from year to year and from locale to locale.

The onset of the rains has a remarkable effect. Within two weeks, brown, lifeless landscapes turn green, seeds germinate and chemical reactions within soils make nutrients available to plants.

From December through March, air masses from the north dominate, creating a long dry season as the rain-producing ITCZ turbulence moves south of the equator.

In the dry season, fields ripen for harvest, pasture grasses shift into dormancy and livestock migrates to pasture near water sources.

As a continent, Africa has the world's sharpest seasonal swings from wet to dry. Vegetation patterns, animal movements, and human economies in Africa have adjusted to this cycle over several millennia.

In the larger geological time frame, Africa's climate has been more often dry than wet and more often warm than cool. The cereal crops native to Africa, such as many varieties of sorghums and millets, or teff and eleusine (finger millet) in Ethiopia, have adapted to seasonal conditions and periodic drought over a millennium or two.

Exotic crops like cassava and bananas — and maize — that originated in either the New World or Southeast Asia, owe their popularity among African farmers to the success with which they have fit into the seasonal systems.