Soil can look like plain dirt at the end of a dry season, but under the surface it is packed with microscopic life that helps decide whether crops struggle or thrive. What if the next boost for farming starts with what is already living in the ground?
Researchers at the National Autonomous University of Mexico, led by Mario Alberto Martínez-Núñez with Quetzalcoátl Orozco-Ramírez, analyzed soils from the Mixteca Alta UNESCO Global Geopark in Oaxaca.
Working through the Institute of Geography, the Academic Unit for Territorial Studies in Oaxaca, and the Observatorio Genómico de Oaxaca, they linked traditional farm landscapes to different mixes of bacteria. Their open access paper is available in the journal Agriculture.
What the study found
The team looked at the soil “microbiome,” the microbes living in soil. They detected 21 major bacterial groups, with four of them making up about four out of five genetic reads. Those top groups were Acidobacteria, Proteobacteria, Actinobacteria, and Chloroflexi.
Why call it an “army”? Because these bacteria are not just passengers. The study links them to core soil jobs like breaking down organic matter and helping limit plant disease.
The researchers also used genetic patterns to predict possible functions. Some pathways were tied to making natural antibiotic compounds that can help block pathogens, the germs that cause plant illness. Others pointed to nitrogen cycling, which matters when farmers try to get more from every bag of fertilizer.
The ancient systems behind the samples
The samples came from three land types shaped by long-term land management, lama-bordos, contour terraces, and valleys. A lama-bordo is a stone wall built across a small channel so water drops sediment behind it, slowly forming a fertile terrace. It is a practical way to fight erosion in steep terrain.
A 2013 study reported that people in the region built lama-bordos at least about 3,400 to 3,500 years ago. The geopark profile also describes lamabordos as a technique designed to trap water and soil, summarized at UNESCO.
This matters for microbes because land shaping changes the soil itself. Trapped sediment can hold more nutrients and moisture, while exposed slopes may stay sandier and drier. Over time, that can favor different bacterial communities.
How scientists identified the bacteria
In May 2023, during the dry season, the team collected multiple soil samples from each land type. They sampled from roughly 8 inches below the surface and compared lama-bordo, valley, and terrace soils side by side. The final analysis compared three lama-bordo samples with four samples each from valleys and terraces.
To identify bacteria, they used 16S rRNA sequencing, a genetic barcode method. Scientists read traces of DNA in the soil and match them to known groups, instead of trying to grow everything in a dish. That helps capture microbes that are hard to culture in a lab.
There is a limit to this approach, and it is worth saying out loud. DNA can show what is present, and software can suggest what microbes might do, but it does not prove that a field will yield more corn or beans next season. It is a map, not a guarantee.
What it could mean for farmers
One result stood out. Valley and lama-bordo soils looked more similar to each other than to terrace soils, even when they were not right next to each other. The researchers link that pattern to soil richness, with nutrient-rich soils supporting one set of bacteria and poorer terrace soils favoring another.
That split points to a practical idea, local biofertilizers and biostimulants made from microbes already adapted to Mixteca conditions.
If those microbes can be turned into products, they could support healthier soil with less reliance on heavy agrochemical use, but they would still need careful field testing. Results can also vary with crop type, rainfall, and everyday farming decisions.
A U.S. Department of Agriculture glossary helps explain what “biofertilizers” are in simple terms. It defines them as beneficial microorganisms applied to plants, seeds, or soil to increase the nutrients available to plants, which is different from compost or manure. The definition is at lod.nal.usda.gov/nalt/en/page/69901.
Why soil health is in the spotlight
The big backdrop is soil degradation. The Food and Agriculture Organization of the United Nations has warned that about one-third of land is moderately to highly degraded. It also notes that soil forms slowly, sometimes taking up to 1,000 years to build less than half an inch.
That helps explain the interest in microbes. Healthy soils are living systems, and microbes help make nutrients usable and keep soil structure stable. It is not a silver bullet, but it is part of the same push to keep farms productive without treating soil like a disposable resource.
For a kitchen table view, soil health can show up as food prices. When soil loses fertility, yields can fall and costs can rise, even for families far away from the field.
What happens next
The next step is moving from discovery to proof. Researchers usually need to isolate promising bacteria, test them in greenhouse and field trials, and confirm they are safe for ecosystems and people. Real-world performance can swing with drought, storms, and changing farm practices.
The regional research unit behind this work was created in 2017 to strengthen the university’s presence in southern Mexico and to support the geopark alongside local communities. Its mission and background are described at UNAM. That connection could make long-term monitoring easier.
For now, the “army” label is a metaphor, but the living workforce is real. The soil already does a lot of work for agriculture, and scientists are learning how to measure it.
The study was published on the journal Agriculture.
