Exciting results from study that examined farmland soil treated only with organic fertilizers

Beneath our feet lies one of Earth’s most overlooked treasures – a thin, living skin of soil that quietly feeds us, shelters us, and helps control the climate by keeping carbon out of the air.

Farmers influence that system every season through how they manage their fields. The question that keeps coming up is: Which practices actually help soil hold on to carbon for the long haul?

Carbon does not stay put by accident. It needs places to settle and forms that resist rapid breakdown.

That is why researchers are paying close attention to how fertilizers and field practices change tiny features within soil where carbon can be stored indefinitely.

Organic soil and carbon storage

A research team examined soil from a Kansas cornfield that has not been tilled for 22 years.

Sections of the same field followed different nitrogen strategies over that period: no fertilizer, synthetic fertilizer (urea), or organic amendments such as manure or compost.

That long record gives a clearer view of real change, rather than short-term swings from weather or a single harvest.

The work comes from Kansas State University and partners who used ultrabright X-ray facilities to analyze intact soil particles.

“We were trying to understand what the mechanisms are behind increasing soil carbon storage using certain management practices,” explains Dr. Ganga Hettiarachchi, professor of soil and environmental chemistry at Kansas State University.

“We were looking at not just soil carbon, but other soil minerals that are going to help store carbon.”

Understanding microaggregates

Soil forms tiny clusters called microaggregates, each about the width of a human hair. Inside them are small pores and mineral surfaces that can trap organic matter.

When carbon enters those protected spaces or binds to minerals, it becomes harder for microbes and oxygen to reach it, which slows decomposition.

These structures build over time through plant inputs, microbial activity, and chemistry at mineral surfaces.

In no-till systems, aggregates are less disturbed, which helps them persist and accumulate carbon-rich material.

How to study soil grains

The team used synchrotron X-ray imaging at the Canadian Light Source in Saskatchewan and the Advanced Light Source in Berkeley, California.

These instruments reveal the chemistry and structure of undisturbed soil grains. This approach avoids grinding or dissolving samples, allowing researchers to see where carbon sits in relation to pores and minerals.

Mapping carbon in place also helps identify which minerals are involved in retention.

Different compounds of iron, aluminum, or calcium can form bonds with organic molecules. Those bonds can slow the carbon cycle in soil and keep more carbon belowground.

Carbon levels and soil plots

In soil plots that received manure or compost, total carbon levels were higher than in plots receiving synthetic fertilizer or no fertilizer.

Imaging of microaggregates showed more carbon in tiny pores and more carbon attached to mineral surfaces in organically amended soil. These locations are associated with longer carbon residence times.

The team also observed higher “microbial carbon” in the compost and manure treatments. That term covers carbon in living microbes and in their remains, often called microbial necromass.

These remnants can become part of the stable carbon pool when they bind to minerals or are embedded inside aggregates.

“To my knowledge, this is the first direct evidence of mechanisms through which organic enhancements improve soil health, microbial diversity, and carbon sequestration,” the authors wrote.

Organic amendments work differently

Synthetic nitrogen can raise yields and add plant material to fields. But organic amendments bring more than nitrogen. They carry a mix of organic molecules, micronutrients, and microbial communities.

That richer input feeds diverse microbes that produce sticky by-products, which help particles bind together and form stable aggregates.

Over many seasons, this activity creates more protected pores and carbon–mineral associations associated with persistence. In a long-term no-till setting, those features accumulate rather than being broken apart.

Impacts for farms and climate

The findings support a practical path: organic amendments can increase soil carbon and place carbon in harder-to-reach spots.

That is relevant for growers who want soils that hold water, resist erosion, and support steady yields.

It also matters for climate since keeping carbon stored belowground reduces the share that returns to the atmosphere as carbon dioxide.

Still, it is not a one-size-fits-all prescription.

Manure and compost supplies vary by region. Transport, application rates, and timing have costs and environmental trade-offs. Local soils and weather shape outcomes.

The evidence here shows how and where carbon is stored under organic additions, which can guide decisions and improve economic and environmental planning.

Time and methods were crucial

Nondestructive imaging gave the team a way to connect cause and effect. Instead of inferring mechanisms from bulk measurements, they could locate carbon directly in pores and on minerals.

That level of detail helps refine computer models that estimate how different practices change soil carbon over years.

Time was essential. The 22-year history of the field allowed processes to play out and stabilize. Soil changes slowly.

Long-term management – especially avoiding tillage – allows aggregates to form, persist, and accumulate carbon that is not easily lost.

Soil, carbon, and Earth’s climate future

Across the no-till field in Kansas, organic amendments placed more carbon in protected pores and on mineral surfaces and supported more microbial carbon. Those changes line up with longer carbon storage.

The work adds a clear mechanism to a topic that often relies on broad averages: not just how much carbon is present, but where it sits and how it is protected.

“Collectively, studies like this are going to help us to move forward to more sustainable, more regenerative agriculture practices that will protect our soils and environment as well as help feed growing populations,” Hettiarachchi concluded.

“As well, understanding the role of the different minerals, chemicals, and microbes involved will help improve models for predicting how different farming practices affect soil carbon storage.”

The full study was published in the Soil Science Society of America Journal.

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