Agriculture has undergone significant changes over the last century, primarily driven by agricultural intensification through improved crop varieties, increased use of agrochemicals, and mechanized tillage.
These changes have played a pivotal role in feeding the growing global population. However, they have also come at a considerable environmental cost, including biodiversity loss, water and air pollution, and contributions to climate change.
As the world's food demand continues to rise, it has become increasingly important to explore sustainable agricultural practices that mitigate these negative impacts.
One critical aspect of sustainable agriculture is the management of soils and overall soil health. Soil biological communities, in particular, have the potential to support food production and provide various ecosystem services.
Earthworms, as important ecosystem engineers, have a significant influence on plant growth through their effects on soil structure, water retention, organic matter cycling, and nutrient availability. They have also been found to facilitate the production of plant growth-promoting hormones and enhance crop immune responses to common soil pathogens.
Despite being recognized as indicators of healthy soils, the precise contribution of earthworms and other beneficial soil organisms to global agricultural production has remained poorly understood. This knowledge gap is crucial for the development of innovative agroecological practices and policies.
Estimating Earthworm Impacts
To estimate the contribution of earthworms to crop production, a study analyzed data on earthworm abundance, soil properties, crop yields, and earthworm-yield responses from existing literature. The findings revealed that earthworms contribute significantly to global crop production, with their impact varying by crop type.
For major cereal crops such as maize, rice, wheat, and barley, earthworms were estimated to contribute approximately 6.5% of global production. This translates to over 140 million metric tons of grain annually.
In the case of legumes, such as soybeans, dry beans, peas, garbanzos, lentils, alfalfa, clover, their contribution was lower at 2.3% of the global total, equivalent to 16 million metric tons. The variation in impact between cereals and legumes can be attributed to the greater influence of earthworms on cereal growth due to the mineralization of organic nitrogen in the soil, which is more beneficial for cereals.
Regional Impacts of Earthworms
The impact of earthworms on crop yields is not uniform across regions. The study found the most significant relative effect in Sub-Saharan Africa, where earthworms contribute approximately 10% of total cereal production and 3.2% of legume production. Latin America and the Caribbean also benefit significantly, with earthworms contributing around 8% of cereal grain and 3.1% of legume production.
These regional variations are influenced by soil characteristics, such as lower pH and higher clay content, which enhance the benefits of earthworms in the global South. In Europe and Eastern/South-Eastern Asia, where earthworm abundance is higher, their impact on cereal grain production is estimated at 7.4%.
However, in regions with lower earthworm abundance, higher fertilizer use, and less favourable soil properties, the contribution of earthworms to crop production is less pronounced.
Recognizing Sources of Uncertainty
The study acknowledges potential sources of error in its estimates. Most studies included in the analysis relied on simple mesocosms with controlled earthworm densities, which may not fully capture the long-term benefits of earthworms under realistic conditions.
Additionally, the analysis assumed simple additive effects of plant and environmental factors, without considering potential interactions among these drivers.
There was also a sampling bias in the data used for estimating earthworm abundance, with a majority of data points from Europe and eastern North America. This bias may lead to an underestimation of earthworm contributions in regions with low representation, such as Sub-Saharan Africa.
Therefore, there is the possibility that the global earthworm map used in the study underestimates both the diversity and abundance of earthworms in these regions.
This study is the first to quantify the contribution of earthworms to global agricultural production. While earthworms were found to have a notable impact, it is important to recognize that other soil biota may also play equally important roles. The study does not advocate for introducing earthworms to regions where they are not naturally present, as this can have negative ecological consequences.
Instead, it emphasizes the need for continued research and promotion of agroecological practices that enhance entire soil biological communities, including earthworms, to support a range of ecosystem services. These practices are crucial for the long-term sustainability and resilience of agriculture in a world where food demand continues to grow, and environmental concerns are paramount.
