By turning a wasted resource into fertilizer, researchers aim to help a hungry nation replenish depleted soils

By Virginia Gewin |

As unemployed young men pick through trash heaps near Jimma University in southwestern Ethiopia to find treasures to sell, they search for one of the hottest resources in demand at the moment: discarded animal bones.

Animal bone is one of Ethiopia’s only sources of phosphorus and calcium, nutrients the country’s acidic, depleted soils have in shortest supply. Most of the country’s 80 million farmers, who comprise 80 percent of the population, cultivate small parcels of the ruddy soils. Despite the fact that Ethiopia is one of the fastest-growing economies in the world, fertilizer often remains an out-of-reach expense. And if farmers are able to buy phosphorus fertilizer, they typically apply only a fraction of what is needed, which diminishes, if not eliminates, the intended effects of the fertilizer. As a result, hectares of stunted maize plants — made worse by the current devastating drought — are a common sight, and 10.1 million households in the sub-Saharan country will rely on food aid this year. In search of nondegraded land, farmers expand operations onto steep mountain sites, which are not ideal for agriculture, either.

In 2011, the U.S. Embassy in Ethiopia spent US$15,000 to foster an agricultural research partnership between Cornell University in Ithaca, New York, and Jimma University, located 350 kilometers (217 miles) from Ethiopia’s capital, Addis Ababa, as a way to both educate students and improve food production in the face of climate change. The partnership quickly seized on the phosphorus dilemma and the potential of the abundant, untapped source of the nutrient going to waste outside slaughterhouses or in garbage heaps across the cattle-rich country.

“There were piles of bones that nobody was using at the time,” says Cornell University soil scientist Dawit Solomon, a native of Ethiopia. Solomon and colleagues decided to turn the mountains of slaughtered cattle, sheep and goat carcasses into a local fertilizer source. In 2013 the researcher calculated that, if recycled, the 192,000 to 330,000 metric tons (212,000 to 364,000 tons) of bone waste each year from livestock could yield 28 to 58 percent of annual phosphorus supplies to the country — saving US$50 million to US$104 million annually were the same amount of fertilizer imported. They proposed setting up a system to collect bones and burn them at high temperatures, a process known as pyrolysis. Pyrolysis eliminates potentially harmful microbes and makes the phosphorus in the resulting bone powder more available to plants when added to the soil. (The team is working separately on trials to address nitrogen and potassium shortages in the soil, but the focus of the bone char research is to provide phosphorus.)

It wasn’t clear how, using Ethiopia’s existing technology, to fashion bone into the familiar, easy to spread, slow-release fertilizer pellets farmers would want. Cornell agricultural economist Garrick Blalock and students from Cornell and Jimma found themselves in uncharted territory — spraying sugar water onto powdered bone, cornstarch and molasses as a motorized spinning disk churned the mixture into sturdy peanut-sized pellets. They finally hit on a winning strategy and are now supporting development of low-cost machinery to produce the fertilizer anywhere in the country.

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