by Rolf Sommer
For farmers in North America, Europe and parts of Asia, growing enough food has never been a problem thanks to a centuries-old practice that leads to high yields: the application of chemical fertilizer to soil. It has become increasingly obvious, however, that this soil-booster—a US$100 billion dollar industry that dates back to the 19th century—is seriously damaging to the environment. Nitrate and other chemicals that comprise fertilizer have polluted streams and lakes and seeped into drinking water supplies, killing wildlife and threatening human health.
Why, then, are soil scientists around the world, many of whom will gather in Berlin next week for Global Soils Week, lobbying for a rapid increase in the use of chemical fertilizers in sub-Saharan Africa. Wouldn’t that mean repeating the mistakes of the developed world?
Not necessarily. Not all soil is created equal—and in sub-Saharan Africa, it’s in bad shape. Most soils in the tropical region aren’t as fertile as soils in the temperate north because they are millions of years old and over time nutrients have been leached. Without the addition of fertilizer, organic or inorganic, these soils can’t achieve the potency necessary to feed the population—expected to quadruple by the end of the century— that relies on these lands for their food.
Africa has only begun to adopt fertilizer as a solution to its infertile soil. In sub-Saharan Africa, farmers apply an average of nine kilograms of fertilizer per hectare per year. In Germany, farmers apply 200 kilograms per hectare per year. As a whole, all farmers across sub-Saharan Africa use only a little more fertilizer than farmers in Germany—a country only about two-thirds the size of Kenya. For Africa, lack of access to fertilizer is evident in low yields, high soil degradation and the rampant depletion of soil nutrients.
Some argue that instead of applying more chemicals to soils, farmers in Africa should turn to environmentally-friendly organic fertilizer, such as manure, compost and plant residues. Indeed, researchers have found that organic fertilizer is better than its chemical counterpart at sustaining soil fertility and health. But an organic-only solution still falls short.
First of all, organic fertilizer produced on-farm does not replenish soils with nutrients, such as phosphor and potassium, that are absorbed by crops and trucked off-farm to markets. Every year, African farms lose 54 kilograms of these essential nutrients per hectare. Without external inputs in the form of mineral fertilizer, farmers can’t get them back.
Secondly, organic resources are in short supply for millions of farmers, especially those in semi-arid climates. Even when they are available, these poor farmers often can’t afford to apply these organic materials to soil. Instead, they use crop residues as livestock feed and straw and manure for cooking, house construction and as a source of income.
Scientists joining me in advocating for responsible use of mineral fertilizer in Africa aren’t ignoring history. We understand that applying only mineral fertilizer to fix the problem is not the answer. We’re simply convinced that supplying farmers in Africa with fertilizer is the only viable solution to increasing crop productivity and food production.
Still, there are ways for both sides of this debate to find common ground. My team of scientists at the International Center for Tropical Agriculture (CIAT) are developing ways to maximize the benefits of fertilizer— relying on both organic and inorganic—through smarter and more site-specific application methods.
We’ve discovered through recent research that if farmers know what fertilizer to use and when to use it, they’ll need less and it will work better. We have found that infrared technology, for example, makes it easier and quicker to test soil quality to determine which nutrients are missing. And from long-term trials in Western Kenya, we know that we can reduce mineral nitrogen fertilizer quantities by half if we combine it with moderate amounts of manure, without jeopardizing maize yields and soil fertility.
Looking for alternatives to fertilizer is also at the top of our agenda. Recent research shows that cutting-edge computer models can be used to advise farmers—based on their specific geographic location—on techniques they can use to improve their yields. CIAT scientists have identified environmentally friendly grasses, for example, that minimize losses of nitrogen to the environment, while enhancing soil health and the likelihood of growing more food—with less inputs.
As long as agricultural policymakers in Africa stay clear of “chemical only” or “organic only” solutions to their agricultural woes, fertilizer offers the continent a real chance of boosting productivity, while using resources efficiently and maintaining healthy soils.