Earthworms contribute significantly to global food production

The intensification of agriculture, while successful in feeding a growing population, has led to significant environmental costs. Agroecological approaches are needed to ensure sustainable food production. Healthy soils are crucial for agroecological intensification, and soil biological communities, particularly earthworms, play a significant role. Earthworms improve soil structure, water retention, organic matter cycling, and nutrient availability, positively impacting plant growth. They also facilitate plant growth-promoting hormone production and trigger crop immune responses. Despite their importance, the quantitative contribution of earthworms to global food production remains poorly understood, hindering the development of effective agroecological practices and policies. This study aims to quantify this contribution for major cereal and legume crops.

The authors utilize a meta-analysis by van Groenningen et al. (2014) that examined the effect of earthworms on plant productivity across various studies. This meta-analysis reported varying earthworm-yield responses based on crop type, soil properties (texture, pH), nitrogen (N) fertilizer inputs, and earthworm abundance. Other relevant literature highlights the multifaceted roles of earthworms in soil health and ecosystem services (Blouin et al., 2013; Fonte et al., 2019; Nielsen et al., 2015). Studies have shown that earthworms can increase plant productivity (van Groenigen et al., 2014), alleviate negative impacts of extreme weather events (Andriuzzi et al., 2015), and contribute to improved crop growth in the long term (Plaas et al., 2019). The impacts of other soil organisms on crop yields have also been studied, for example the impact of ants and termites (Evans et al., 2011). However, a comprehensive quantification of earthworm’s contribution to global food production is lacking, making this study novel and important.

This study estimates earthworm impacts on major cereal (rice, maize, wheat, barley) and legume crop productivity using data from multiple sources and a novel analytical approach. Global crop yields and harvest areas were obtained from Monfreda et al. (2008), while soil pH and texture data came from SoilGrids (Poggio et al., 2021). Nitrogen application rates were adapted from Mueller et al. (2012). Global earthworm distribution data was taken from Phillips et al. (2019). The analysis incorporated the meta-analysis results from van Groenigen et al. (2014), which provided average earthworm effects on plant biomass and identified key drivers of these effects (crop type, soil pH, soil texture, nitrogen application rate, and earthworm abundance). A weighted coefficient for each factor was calculated based on effect sizes and sample sizes reported in the meta-analysis. These coefficients were used to scale the average earthworm effect (23.3% increase in plant production) based on the specific conditions in each grid cell. A nonlinear function was used to model the effect of earthworm abundance. The overall earthworm effect for each grid cell and crop was calculated using equation (1) in the paper. This equation incorporates the coefficients for crop type, soil pH, soil texture, nitrogen application rate, and earthworm abundance. Maps of earthworm effects for each crop were generated and masked to each crop’s production area. To estimate absolute crop yields attributable to earthworms, the calculated earthworm effect was applied to individual crop yield layers, and the difference in production was summed across grid cells. Finally, regional impacts were calculated using United Nations Sustainable Development Goals regional groupings.

The analysis revealed that earthworms contribute approximately 5.4% of global production for the major cereal and legume crops considered. For cereal crops alone, the contribution is estimated at 6.45% (roughly 128 million metric tons of grain), while for legumes, it is 2.3% (16 million metric tons). The difference is attributed to legumes’ nitrogen-fixing capacity, reducing their dependence on earthworm-facilitated nitrogen mineralization. Regionally, the highest relative effect of earthworms was observed in Sub-Saharan Africa (10% of cereal production, 3.2% of legume production) and Latin America and the Caribbean (8% of cereal production, 3.1% of legume production). These higher impacts are associated with lower soil pH, higher clay content, and lower fertilizer inputs in these regions. Europe and Eastern/South-Eastern Asia also showed relatively high earthworm contributions (7.4% of cereal production). In absolute terms, Eastern/South-Eastern Asia and Europe showed the highest earthworm contributions to total cereal grain production (over 40 million metric tons in each region). This reflects the higher overall productivity and expansive cropping areas in these regions. While Sub-Saharan Africa and Latin America and the Caribbean had smaller absolute contributions, even modest increases in these regions are crucial for addressing food security issues.

This study provides the first quantification of a beneficial soil organism's contribution to global agricultural production. The significant contribution of earthworms highlights the importance of soil biodiversity for food security. The findings emphasize that promoting agroecological practices that enhance soil health, including earthworm populations, is essential for sustainable agriculture. The study does not advocate for widespread earthworm inoculation, which can have negative ecological consequences. Instead, it promotes investment in research and implementation of agroecological management to support entire soil biological communities, enhancing ecosystem services and ensuring long-term agricultural sustainability. The regional variations in earthworm contributions underscore the context-dependency of these effects and the importance of tailoring management strategies to specific soil and environmental conditions. The higher contribution in the global South, despite lower absolute production, highlights the potential for impactful interventions in regions facing food insecurity challenges.

This study quantifies the significant contribution of earthworms to global grain and legume production, highlighting the importance of soil biodiversity for sustainable agriculture. The results underscore the need for agroecological practices that support earthworm populations and overall soil health. Future research should explore the contributions of other soil organisms and investigate the complex interactions between soil biodiversity, management practices, and crop yields in diverse agro-ecosystems. Further studies are needed to refine the estimates of earthworm abundance, particularly in data-sparse regions, and to better understand the long-term impacts of earthworms on soil functions and crop production.

Several sources of uncertainty exist in this study. The meta-analysis data primarily relied on mesocosm experiments, which might overestimate the earthworm effect due to sometimes unrealistic densities. The short-term nature of these experiments may not fully capture the long-term benefits of earthworms. The analysis assumed simple additive effects, ignoring potential interactions between environmental factors and earthworm impacts. The global earthworm abundance map had a sampling bias toward the global North, potentially underestimating earthworm contributions in the global South. Global data layers also have inherent uncertainties that can compound in this type of analysis. The spatial resolution of data layers used in the study might affect the accuracy of the estimations.