Rahul Somvanshi
Pick up a handful of garden soil and you are holding a mix of organisms: bacteria, fungi, protozoa, nematodes and more. According to the United Nations Food and Agriculture Organization (FAO), these organisms together make up what is known as soil biodiversity.
The FAO describes several specific functions this biodiversity performs. Soil organisms drive nutrient cycling. They help regulate soil organic matter, soil carbon sequestration and greenhouse-gas emissions. They modify the soil’s physical structure and its water regimes. They enhance the amount and efficiency of nutrient acquisition by vegetation. They also contribute to plant health. None of this is visible from the surface, but it is activity with effects that reach beyond the soil itself.
A food web shaped from above
Soil organisms do not operate in isolation from what grows above them. Research compiled by the U.S. Department of Agriculture’s Agricultural Research Service finds that increasing plant biomass and diversity provides larger and more diverse food sources for soil organisms at all trophic levels (USDA ARS). That finding is a useful reminder that soil biodiversity is part of a wider ecological system, rather than a separate world beneath the surface.
Biologically active, biologically diverse
The USDA’s Natural Resources Conservation Service describes soil as biologically active and diverse (USDA NRCS). It is a deliberately simple description, and it is worth not reading more into it than the source states. The organisms named by FAO are different parts of that diverse community, with documented roles in processes that matter for ecosystems and agricultural systems alike.
Where the popular comparison breaks down
A striking claim often circulates alongside facts like these: that a handful of soil contains more microorganisms than all the humans who have ever lived. It is a vivid way to make a point, but this comparison is not established by the FAO, USDA ARS or USDA NRCS sources referenced here. None of them puts a number on soil organisms or compares such a number with human population figures. The claim should not be read as a measured fact or attributed to these sources.
What the sources do support is narrower, but still substantial. Soil hosts a biologically active and diverse community of organisms. That community cycles nutrients, helps regulate organic matter and carbon in soil, affects greenhouse-gas emissions, modifies soil structure and water regimes, and helps vegetation acquire nutrients more effectively. Larger and more diverse plant growth above ground provides a larger and more diverse food supply for that community. These are specific, documented functions—not a single dramatic number, but a traceable set of processes.
That is the more reliable way to talk about what is underfoot: not as a record-breaking population count, but as a working system with identifiable roles documented by the agencies that study it. The next time a shovel turns over a patch of ground, it is worth remembering that the soil contains a community carrying out those quiet, specific functions.
