Earthworms are important drivers of global food production, contributing to approximately 6.5% of grain yield and 2.3% of legumes produced worldwide each year, according to new work published by Colorado State University scientists in the journal Nature Communications.
Estimates from CSU researchers mean earthworms may account for as much as 140 million metric tons of food produced annually - roughly comparative to the amount of cereal grains (rice, wheat, rye, oats, barley, maize and millet) grown annually by Russia, the world's fourth-largest producer.
"This is the first effort that I'm aware of that's trying to take one piece of soil biodiversity and say, 'this is the value of it; this is what it's giving us on a global scale,'" said Steven Fonte, the study's lead author.
Earthworms help establish healthy soils by supporting plant growth in multiple ways - building good soil structure, assisting in water capture and aiding in the beneficial churn of organic matter that makes nutrients more available to plants. Other research has shown that earthworms can facilitate the production of plant growth-promoting hormones and help plants protect themselves against common soil pathogens. Some estimates have indicated that earthworms can increase overall plant productivity by about 25%.
Fonte and his colleagues Nathan Mueller and Marian Hsieh, who is supported by a U.S. National Science Foundation Graduate Research Fellowship, estimated the contribution of earthworms to global food production by overlaying and analyzing maps of earthworm abundance, soil properties, fertilize rate and crop yields.
Their analysis indicated that earthworms had a more significant impact on grain production in the global south - notably, 10% of grain yield in sub-Saharan Africa and 8% in Latin America and the Caribbean. It's likely the earthworms contributed more in these areas, Fonte said, because farmers there tend to have less access to fertilizer and pesticides. Instead, they rely more on earthworm-rich organic matter like manure and crop residues, which help stimulate the beneficial effect earthworms have on plants.
"Earthworms are contributing a lot in these areas where we have fewer chemical inputs," Fonte said. For the study, the researchers analyzed earthworm impacts on four grain crops: rice, maize, wheat and barley. The group examined a set of legumes that included soybeans, peas, chickpeas, lentils and alfalfa, among others. Fonte said he thinks soil biodiversity has historically been undervalued, and that he hopes this work will bring more attention to ways healthy soils can have positive, tangible impacts on crops.
