State of the Planet

News from the Columbia Climate School


Revitalizing Africa’s Soils

Farmers in Tanzania. Photo: Gates Foundation
Farmers in Tanzania. Photo: Gates Foundation

A new study by the United Nations projects that, contrary to previous estimates, the world’s population will not stabilize in 2050, but may grow to 12.3 billion by 2100. Much of this growth will occur in Africa, where the population is expected to quadruple to 4 billion.

To feed our burgeoning global population, the world has to at least double crop yields by 2050, and in order to do this, we need to both improve seeds of high yielding crops and cultivate healthy fertile soils, according to Pedro Sanchez, director of the Earth Institute’s Agriculture and Food Security Center. A new on-the-spot soil testing kit has been developed by researchers at Columbia University and the University of Maryland to meet this challenge.

The 68th UN General Assembly designated 2015 the International Year of Soils to raise global awareness about the importance of “healthy soils for a healthy life.” Soils produce food, fuel, fibers, sustain plant and animal life, cycle nutrients and help provide clean water and other ecosystem services such as carbon storage.

The amount of fertile soil on Earth’s surface is limited and not renewable in human time frames. In the last 150 years, half of Earth’s topsoil has been lost, with more being continually degraded through deforestation, over-tillage, irrigation and soil salinization, excessive use of nitrogen fertilizers, acid rain, pesticides and chemical fertilizers, overgrazing and compaction by heavy equipment.

Nkhoma's farm

The soil in many parts of Africa is poor and crop yields are inadequate because farmers have planted intensively without replenishing the soil’s nutrients. While the U.S. and Japan produce approximately 10 tons of crops per hectare, Africa produces only one ton of crops per hectare. In some parts of Africa, crop yields have doubled and tripled mainly due to the application of expensive and inefficient mineral fertilizers and improved seeds, but in order to use nutrients and water more efficiently in a world where agriculture will be increasingly affected by climate change, farmers need specific recommendations that take their local climate, soils, crops and potential crop yields into consideration.

“We know a lot about how to improve soil health with fertilizer, manure and tillage practices,” said Sanchez. “But the recommendations need to reach the farmers or they’re useless.”

The new SoilDoc kit can do on-the-spot soil testing to assess the availability of nitrogen, phosphorus, sulfur, potassium and active organic matter (microbes), and the amount of compaction of the soil. The kit makes it possible to provide specific and timely recommendations to make the soil more fertile.

“It’s just like the doctor coming to see the patient,” said Sanchez. “But in this case, the patient is soil.”

Traditionally soil samples are mailed to a lab for testing. There are commercial soil labs in developing countries that can analyze soil and make recommendations, but these analyses are relatively expensive (costing $30 to $50 each), and require electricity and distilled water, which are sometimes hard to come by, explained Sanchez. Moreover, most national labs are overwhelmed, so recommendations may take a long time—so long, in fact, that sometimes they are no longer relevant by the time they arrive.

3 extension workers wearing SoilDoc kits
Extension workers wearing SoilDoc kits

By comparison, the SoilDoc kit is battery-operated, uses bottled water instead of distilled, takes one to two days to produce results, and costs only about $3 per analysis. The kit, which can be carried as a backpack, produces results as accurate as those of commercial labs, and it can be used anywhere.

Kenyan Lydiah Gatere, a post-doctoral fellow in soil science at the Agriculture and Food Security Center, is currently the main trainer for the kit. She has trained extension workers in Nigeria, Tanzania and Zambia to use the kit—either government workers who give farmers advice on planting, or private company workers who contract farmers to provide service. Some of them, in turn, will teach others.

I visited Gatere at a Lamont-Doherty Earth Observatory lab to learn how the process works as she was training four agronomists.

First, about 10 randomized samples of soil are taken from the main field a farmer relies on for food. The samples should be representative of a field’s slopes, soil texture and soil color. The soil samples are mixed up in a bucket and sieved; then a tiny amount is mixed with bottled water in a tube. The sample is shaken for 2 minutes—at this point, the farmer and his family are often invited to join in the shaking process.

Lydiah Gatere teaching agronomists
Lydiah Gatere training agronomists at LDEO

Once the soil settles in the tube, a pH meter borrowed from the beer industry is used to test the acidity of the water in the tube. The water is then tested with miniaturized sensors for salinity, nutrients (sulfur, potassium, phosphorus and nitrate) and biologically active organic matter. The results are entered into a program on an Android tablet and sent to the cloud. A lab director analyzes the information and makes recommendations to the extension worker.

Each soil sample will eventually be given its own barcode, then test results will be sent via SMS through a cell phone to a database in the cloud. Right now, recommendations for improving the soil are made by soil experts based on their own knowledge and experience, but in the future, said Sanchez, algorithms will be able to make recommendations automatically.

Two other tests are also performed: The texture of the soil is determined by human feel, and a separate small instrument assesses the compaction of the soil. If the soil is very compacted, recommendations may be made for more tilling or the addition of extra organic matter.

While general blanket recommendations for soil fertility exist in Africa, they are usually national or regional and don’t account for an area’s specific characteristics. Moreover, they are usually holdovers from post-colonial times and thus irrelevant to today’s soil conditions, explained Gatere. She and Sanchez, Cheryl Palm, director of research at the Agriculture and Food Security Center, and soil scientist Ray Weil, who developed the SoilDoc kit, are working on new recommendation standards based on data gathered through the kit.

Gatere testing soil samples on a veranda
Gatere testing soil samples on a veranda

Bringing the kits to market commercially will likely take another year. Currently, the SoilDoc kit is in test mode. There are five kits in Zambia, 15 in Tanzania and 100 in Nigeria.

“We are doing ‘proof of concept’ experiments in various countries,” said Gatere. “We are applying fertilizer based on the recommendations. Once you get a yield, then you can calculate to see how much fertilizer you need to get the maximum yield…And we will be working with fertilizer companies, because if an area needs more of something, we will ask them to blend the fertilizer to suit the specific needs of the farmers.”

In Tanzania and Malawi, Gatere also studied whether farmers will pay for the service, and if they will implement the recommendations they receive.

Because Africa has a lot of tech-savvy university graduates, Sanchez wants to recruit them to use their IT capabilities to transform the existing extension services. He’s hoping that the technical aspects of the SoilDoc kit will entice young people to become extension workers or form their own companies to bring technology to the farmers.

Training data management on the Android
Training data management on the Android

Eventually, data from the kits will be melded with the global digital soil map  being developed by the African Soil Information Service. The digital soil map provides top-down information about clay and organic carbon with data from satellites and drones; the kits will provide on-the-ground local data about nutrients in the soil.

The farmers like being able to know what kind of fertilizer to apply to their fields and how much, Gatere said. One soil scientist working in a Zambian national lab told her, “This kit is what I’ve been waiting for my whole life.”


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Juan Trescothick
9 years ago

Extraordinary and Insightful! It really stunned me to read that world’s population will grow from quadruple to 4 billion especially in Africa. 6% of total earth surface is covered by Africa and it is obvious that with so much growth in population would require more cultivation to feed them. Healthy soil is a vital part of the environment and it effects the distribution of plant species for a wide range of organisms.

I was unaware of SoilDoc kit so thanks for the update on it. This is indeed a very useful technological development for farmers and surely it will attract many young people to open their own farming companies. I am truly impressed after reading your blog as it gave immense satisfaction that to feed the future growing population innovative steps are taken and developed in advance. I hope this kit will really come in handy in order to improve the soil fertility. Thanks for narrating the whole process.

9 years ago

Good post Renee. Thanks for your information.
Lets save africa.