In a recent publication in the journal Nature Communications, US scientists conducted a study to assess the significance of earthworms in global food cultivation. Their findings highlight the importance of sustainable agricultural management and increased investment in agroecological policies to ensure food security while preserving soil health and biodiversity.
Over the past century, the escalating global population has driven farmers to enhance yields through the adoption of new crop varieties and increased use of machinery, fertilizers, and pesticides. However, these practices have adversely impacted soil health and biodiversity, contributing to air and water pollution and climate change. As the demand for food rises, sustainable production becomes imperative.
Earthworms, often termed ‘ecosystem engineers,’ play a vital role in agriculture by aerating, hydrating, enriching soil with nitrogen, and protecting crops from pathogens. Recognizing these benefits, scientists sought to quantify the impact of earthworm activities on agriculture to manage croplands more efficiently and enhance yields in an environmentally friendly manner.
The researchers collated existing literature on the effects of earthworms on agriculture, drawing evidence from experiments involving the removal or addition of earthworms to greenhouses or fields. These studies allowed them to estimate the average effect of earthworms across diverse settings, referred to as the ‘overall earthworm effect’ (E).
The research team employed global maps of agricultural lands to examine the cultivation of specific crops, focusing on cereal grains (e.g., barley, maize, rice, and wheat) and legumes (such as soybean and peas). Various factors influencing crop yield, such as soil acidity and texture, were taken into account.
Additionally, distinctions were made between areas receiving high rates of nitrogen fertilizers and those that did not. Another set of maps was utilized to estimate earthworm abundance, indicating the size of the earthworm population in each geographic area.
These maps, along with the earlier estimated overall earthworm effect (E), were utilized to quantify the contribution of earthworms. The calculation considered the cultivated area for each crop, factoring in elements like soil acidity, texture and nitrogen. The impact of earthworms was further assessed for each global region, aligning with the classifications outlined in the United Nations Sustainable Development Goals.
In the absence of earthworms, cereal production would experience a 6.45% decline, equivalent to 128 million metric tons annually. While their impact on legumes is less pronounced, it remains significant at 2.3% contributing to 16 million metric tons each year. The authors attribute this difference to legumes having the ability to fix their own nitrogen, reducing dependence on earthworms.
Examining regional significance, earthworms play a pivotal role in Sub-Saharan Africa, responsible for one-tenth of cereal grain crops and slightly over 3% of legume crops. Latin America and the Caribbean also witness substantial contributions, accounting for 8% of cereals and 3.1% of legumes. In South-Eastern Asia, their importance lies in cereal grain growth, making up 7.4%.
Analyzing regional yields, the most substantial contribution of earthworms occurs in Eastern/South-Eastern Asia and Europe, totaling 40 million metric tons of cereal grains. This is likely attributed to the high earthworm populations in these regions, which also boast greater cereal production and more cultivated land. While contributions are comparatively lower in Sub-Saharan Africa (3 million metric tons) and Latin America (22 million metric tons), they remain indispensable for ensuring food security.
The authors go on to say, “Our results are encouraging and suggest significant potential to enhance agricultural productivity via improved management of soil biological communities.”
This groundbreaking study marks the first attempt to quantify the global significance of earthworms in agriculture and nutrition. Earthworms annually contribute 140 million metric tons to legume and cereal production, particularly in soils with lower pH and higher clay content, where fertilizer use is minimal.
The scientists adopted a conservative approach, acknowledging the potential underestimation of these small animals’ contribution. Many of the experiments they examined were brief and lacked assessments of long-term effects, such as protection against erosion.
The team highlighted that while the relationship between earthworms and agriculture is well-explored in Europe and North America, there is limited knowledge in Africa and Asia. There may also be an underestimation of earthworm abundance, impacting the study’s results, and providing fertile ground for further scientific exploration. The study highlights the need to explore the roles of other soil organisms.
Regardless of these promising results, scientists caution against interpreting them as a justification for releasing earthworms into areas where they are scarce, as this could have adverse effects. Instead, they advocate for ongoing promotion and research of agroecological management practices that enhance biological communities in the soil, including earthworms. These practices contribute to safeguarding soil biodiversity and promoting 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,” the authors note.