State of the Planet

News from the Columbia Climate School

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Why Soil Matters

Photo credit: visionshare

Soil is the source of all life. Yet “we know more about soils of Mars than about soils of Africa,” says Pedro Sanchez, director of the Earth Institute’s Tropical Agriculture and the Rural Environment Program. To remedy this situation, the Earth Institute is taking part in an ambitious undertaking to map the world’s soils.

Soil provides nutrients that sustain plants for food and energy, and anchors their roots. By absorbing, releasing and purifying most of the water on earth, it supplies us with drinking water, regulates excess rainfall and prevents floods.

Much of the planet’s biodiversity resides in the soil: it’s estimated that an acre of soil may contain 900 pounds of earthworms, 2400 pounds of fungi, 1500 pounds of bacteria, 133 pounds of protozoa, 890 pounds of arthropods and algae, and even sometimes small mammals. One gram of soil may hold one billion bacteria, of which only 5 percent have been discovered.

Soil acts as a buffer against pollutants such as heavy metals and excess nutrients. Moreover, soil is critical in helping slow climate change—as the largest carbon sink on land, it stores over three times more carbon than forests and other vegetation.

It can take 500 to 1,000 years for one inch of topsoil (the upper layer of soil containing the most organic matter and microorganisms) to form through the interaction of bedrock, climate, topography, and living organisms. Soil erosion has always occurred naturally, but sometime during the 19th century, the rate of topsoil loss from erosion due to agriculture surpassed the rate of soil formation, according to Lester Brown, president of the Earth Policy Institute.

Today “soil is a threatened natural resource,” warns the International Soil Reference and Information Centre (ISRIC – World Soil Information).

Graphic: Philippe Rekacewicz, UNEP/GRID-Arendal

Seventeen percent of the world’s soil has been “strongly degraded” and areas of degradation are growing. Unsustainable agricultural practices are the chief causes of land degradation: land clearing and deforestation to plant crops remove vegetation and change the composition of soils; over-tillage destroys the top layers of soil and hastens erosion; irrigation and soil drainage cause soil salinization after crops take up water and leave salt behind; excessive use of nitrogen fertilizers and acid rainfall acidify soils; pesticides and chemical fertilizers change the consistency of soil and destroy organisms that aerate the soil; and heavy farming equipment compacts soils.

In addition, overgrazing strips soil of vegetation, making it vulnerable to erosion from wind and water, and causes desertification and dust storms.

Dust storm in Australia. Photo: Ian Armstrong

Huge dust bowls are now forming in northern and western China, western Mongolia, central Asia and in central Africa. In 2010, the United Nations reported that desertification affects 25 percent of earth’s land area and jeopardizes the livelihoods of over one billion people in 100 countries.

To feed the global population, now 7 billion and expected to reach 9 billion by 2050, we will need 70 percent more food than we are currently producing (100 percent in some developing countries). Yet, a third of the world’s cropland is losing topsoil at an alarming rate, resulting in lower crop yields. For example, for each inch of topsoil that is lost in the U.S., wheat and corn yields decrease almost 6 percent. As temperatures rise due to climate change, desertification in dry areas will intensify, extreme weather events will multiply and “… agriculture will increasingly be out of sync with the climate system that shaped it,” according to Lester Brown. Each 1-degree Celsius rise in temperature above the optimum during the growing season, will likely result in a 10-percent decline in grain yields.

In 1994,193 countries signed the U.N. Convention to Combat Desertification, acknowledging that soil and water conservation practices are necessary to increase biodiversity, help mitigate climate change and improve food security. The sustainable land management practices needed to conserve soil and boost production have long been recognized: planting grass, leguminous crops (to add nitrogen) and trees for vegetative cover; strip cropping; no till and minimal till techniques; efficient irrigation strategies and the addition of organic matter and fertilizer. But knowing what to do when and where requires a thorough understanding of an area’s specific soil properties and of how different soils respond to different agricultural techniques—so access to methodologies, standardized tools, models and accurate and detailed up-to-date maps is key.

Existing maps of the world’s soils, based on pre-computer age technology, are limited by low resolution and outdated information, or cover only a third of the planet’s ice-free surface. For example, the FAO world soil map, created between the 1970s and the 1990s, has a scale of 1:5 million (1 inch on the map equals 5 million inches on the ground).

Today high-resolution digital soil maps are being produced with new technologies. Digital soil maps are not actually maps in the traditional sense, but rather databases of soil properties compiled from the monitoring of soil and landscape characteristics through the use of technologies including satellite imagery, infrared spectroscopy (a way of analyzing the properties of soils by measuring their absorption of infrared radiation), methods of statistical modeling, field sampling of soils to predict the properties of soil in unsampled areas, enhanced pixel display, and the inclusion of historic information.

AfSIS coverage. Graphic: AfSIS

Under the auspices of the Africa Soil Information Service (AfSIS) and the Consortium, the initial segment of the global soil mapping effort was launched in 2009 in sub-Saharan Africa, where 265 million people do not have enough food. The International Center for Tropical Agriculture is leading the project, with major subgrants to the Earth Institute and the World Agroforestry Centre in collaboration with the International Soil Reference and Information Centre and numerous partners on the ground in more  than 20 African countries. The project is funded by an $18 million grant from the Bill and Melinda Gates Foundation and the Alliance for a Green Revolution in Africa.

The result will be a digital soil map 5 million times more detailed than the FAO soil map, of an area encompassing 42 countries and 90 percent of Africa’s population. The map will also incorporate data on land use, farming systems, crop yields, extent of poverty, roads, etc. The Earth Institute’s Center for International Earth Science Information Network is helping create information systems to collect, analyze, and distribute the data to a wide range of users.

The information will provide a baseline of soil conditions in sub-Saharan Africa, and aid in the development of evidence-based options for sustainable soil management. Models will be able to predict the efficacy of different soil management strategies under different soil, climatic and socio-economic conditions.

Pedro Sanchez, project director for AfSIS, says, “We are on track to release the digital soil maps of Africa in the next few months…and a renewal of the Gates Foundation grant looks very promising.” A second phase of the project, which would be renamed AfricaSoils and begin in November, would focus on Ethiopia, Nigeria, Ghana and Tanzania, and concentrate on the data aspects of the project, as well as the development of and training; while on-the-ground field sampling efforts are being conducted by government agencies, like the Agricultural Transformation Agency in Ethiopia. In addition, a new tool called lab-in-the-box will soon enable soil samples to be analyzed in the field with data sent via smartphone apps as well as text messaging, avoiding the time-consuming process of sending samples to a lab for results. Consortium partners are also developing digital soil maps in: East Asia, EurAsia, Latin America and the Caribbean, North America, Oceania, and Central-West Africa/North Africa. The wealthier regions have already begun work, while Latin America, the Mid-East and East Asia are looking for funding.

A Ugandan farmer. Photo: Neil Palmer CIAT

The digital soil maps will be made available online for free, and have many uses in different regions. For example, they will enable governments to anticipate and plan for the fertilizer needs of their farmers, determine the scope of their countries’ erosion and estimate costs to combat it, and help scientists predict the effects of climate change.

Farmers will be able to use the information to figure out the right strategies for their own soils, such as how best to manage fertilizer application rates, inputs of organic matter, irrigation, use of legume planting and tillage techniques.

Says Sanchez, “The digital soil maps will make a huge difference in what you can recommend for use with different kinds of soil, and for helping with climate change, water resources and biodiversity. And most importantly, it will help determine where you put your investments to get people out of hunger in Africa.”

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Joan Angus
6 years ago

I would like to use one of your pictures in the Winter edition of the GreenSpirit magazine, to illustrate an article about Compost. How can I get permission?
GreenSpirit is a national movement of like-minded people. The magazine is crculated to members who have paid a membership fee.

Sarah Fecht
Reply to  Joan Angus
6 years ago

These photos were taken from the creative commons. You’ll have to go to the original creators (cited in the captions) in order to see what permissions they allow.

Shaylee Packer
Shaylee Packer
3 years ago

I didn’t realize that soil provides the nutrients that sustain plants for food and energy. That does make sense though. We are looking to have a garden next year, but the soil in our yard has a high gravel concentration. How much top soil would we need to bring in to sustain a garden?