In a recent study published in the journal Nature Communications, scientists from the US calculated the importance of earthworms for food cultivation worldwide. Their findings highlight the need to manage agriculture sustainably and invest more in agroecological policies promoting food security while protecting soil health and biodiversity.
Study: Earthworms contribute significantly to global food production. Image Credit: Bukhta Yurii / Shutterstock
Background
In the past century, farming has had to keep pace with quickly growing human populations. Farmers increased their yields by planting new crop varieties and using more machines, fertilizers, and pesticides. However, these practices affected the health of the soil and its biodiversity. They caused air and water pollution and contributed to climate change. While demand for food is increasing, production should rise sustainably.
Earthworms contribute to agricultural production in many ways. They are so beneficial that they are often called ‘ecosystem engineers.’ Earthworms help aerate, hydrate, and enrich soil with nitrogen and even protect crops from pathogens. Knowing these mechanisms, scientists aimed to estimate how much their activities affect agriculture. This can help manage croplands and increase yield in an environmentally friendly way.
About the study
Scientists searched published literature, putting together all the research examining the effects of earthworms on agriculture. Their evidence came from experiments that removed or added earthworms to a greenhouse or field. Using these studies, they were able to approximate the average effect that earthworms have across different areas and settings or the ‘overall earthworm effect’ (E).
The team also used global maps of agricultural lands, looking at the crops grown there, particularly cereal grains (such as barley, maize, rice, and wheat) and legumes (such as soybean and peas). They considered aspects that affect crop yield, such as soil acidity and texture. They also differentiated areas that receive high rates of nitrogen fertilizers from those that do not. Other maps were used to estimate earthworm abundance, which was the size of the earthworm population in each area.
These maps and E (which they had estimated earlier) were used to calculate how much earthworms contribute. This was based on the area under cultivation for each crop, including factors such as soil acidity, texture, and nitrogen. They also calculated the impact of earthworms for each global region, using the groupings named in the United Nations Sustainable Development Goals.
Results
Without earthworms, the production of cereals would be 6.45% or 128 million metric tons lower every year. Their contribution to legumes was lower but still significant, at 2.3% or 16 million metric tons annually. According to the authors, this difference is caused by legumes fixing their own nitrogen so they are not as dependent on earthworms.
Regarding regional contribution, earthworms were most important in Sub-Saharan Africa. They were responsible for one-tenth of cereal grain crops and slightly over 3% of legume crops. Earthworms also contributed significantly to cereal and legume production in Latin America and the Caribbean (8% of cereals and 3.1% of legumes). In South-Eastern Asia, their importance was in the growth of cereal grains (7.4%).
However, looking at regional yields, the contribution of earthworms was highest in Eastern/South-Eastern Asia and Europe, at 40 million metric tons of cereal grains. This was probably because earthworm populations are high in these regions. These areas also produce more cereals and have more land under production. The contributions were lower in Sub-Saharan Africa (3 million metric tons) and Latin America (11 million metric tons) but are still crucial for food security.
“Our results are encouraging and suggest significant potential to enhance agricultural productivity via improved management of soil biological communities.”
Conclusions
This is the first study to quantify the importance of earthworms for agriculture and nutrition globally. Earthworms contribute 140 million metric tons to legume and cereal production every year. They have a crucial role in soils with lower pH and more clay, where fertilizer use is not high.
The scientists were conservative in their approach and feel that they might even have underestimated the contribution of these small animals. For example, the experiments they found were often short and did not measure long-term effects like protection against erosion.
The team also noted that the relationship between earthworms and agriculture is well-studied in Europe and North America, but little is known in Africa or Asia. Scientists may also be underestimating the abundance of earthworms, thus affecting the results. These are all fertile avenues for more scientific investigation. The role of other soil organisms should also be explored.
These promising results, scientists caution, should not be interpreted to mean that earthworms should be released into areas where they are currently rare. This could have adverse effects. They instead advocate for ongoing promotion and research of agroecological management practices that boost the biological communities in soil, which includes earthworms. These practices help protect soil biodiversity and support sustainable agriculture and resilient ecosystems.
“Instead, we suggest investment in continued research and promotion of agroecological management practices that enhance entire soil biological communities, including earthworms, so as to support a whole range of ecosystem services that contribute to the long-term sustainability and resilience of agriculture.”
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