How perennial crops could transform sandy soils
Sandy soils have long been considered one of agriculture’s weakest link: dry, leaky, and poor in organic matter. But a decade of Danish field trials shows that replacing annual crops with deep-rooted perennials can help transform these fragile soils. The results reveal a hidden biology that both unlocks nutrients for plants and locks away carbon helping to mitigate climate change.
For generations, farmers have battled with sandy soils: they dry out in drought, leach nutrients in rain, and hold little organic matter. To both farmers and climate researchers, they have long seemed like the weak link of European agriculture.
But below the surface, something remarkable is happening. After ten years of continuous field trials, researchers have found that one simple change: replacing annual crops with the perennial grass tall fescue, reshapes the hidden biology of sandy soils in ways that both release nutrients for plants and lock carbon into the ground for the long term.
“We were surprised to see just how much the biology of the soil shifted,” says Mingming Zong, a Postdoc researcher at Aarhus University and lead author of the study. “The microbes became more efficient at making nutrients available while, at the same time, the soil held on to more stable forms of carbon.”
Microbial scissors at work
In the topsoil, 0-20 centimetres beneath the surface, tall fescue boosted the activity of N- and P-related hydrolytic enzymes, that is proteins produced by microbes that act like biological scissors. These enzymes cut up complex organic matter, freeing nutrients such as nitrogen and phosphorus.
Because the crop was harvested three times a year for use in biorefineries, large amounts of nutrients were removed from the field. Faced with shortages, microbes adapted by producing more enzymes to unlock nutrients directly from the soil’s organic matter.
At the same time, the activity of another kind of enzymes called oxidative enzymes, that normally attack tougher compounds such as lignin, was suppressed. This subtle shift in enzyme balance meant that while nutrients became more available to plants, the most resistant forms of carbon in the soil were left intact.
Fact box: What is lignin? Because it decomposes so slowly, lignin plays a crucial role in soil carbon storage. Plant residues rich in lignin are one of the ways carbon tends to stay in the soil for much longer. That is why researchers pay close attention to enzymes that break down lignin: when their activity is suppressed, more carbon tends to remain in the ground. |
“It’s a double advantage,” Mingming Zong explains. “The system feeds itself by recycling nutrients, but it also slows the breakdown of resistant organic matter. That helps safeguard carbon in the soil.”
Deep roots, deep change
The transformation didn’t stop at the surface. In deeper layers, 20-50 centimetres down, soils under tall fescue held more microbial biomass carbon, a clear sign that the plant’s extensive root system was feeding microbial life far belowground.
Analyses also revealed a tendency toward greater amounts of mineral-associated organic carbon. It is the type of carbon that binds tightly to soil particles and can remain stable for decades or even centuries.
“Deep perennial roots don’t just stabilise the soil mechanically,” says Mingming Zong. “They actively stimulate life in the subsoil and help build long-lasting carbon reservoirs. That’s one of the best insurance policies we have against carbon loss in a changing climate.”
Shifts in carbon chemistry
Using advanced infrared spectroscopy, the team documented a clear shift in the chemical forms of soil organic carbon under tall fescue. In the topsoil, carbon became more stable; in the subsoil, deep roots appeared to feed and protect the long-lasting carbon pools.
Together, these changes add up to a consistent pattern: perennial roots enhance nutrient cycling while at the same time fortifying soil carbon stocks.
From weak link to climate ally
For decades, sandy soils have been considered marginal: low fertility, high vulnerability, little contribution to climate goals. This new study suggests that perennials could flip that narrative. Even under the pressure of intensive biomass harvest for green energy, tall fescue maintained productivity while steadily improving soil health.
“Agriculture is under enormous pressure to deliver food, feed, and energy while also addressing climate change,” says Mingming Zong. “Our results show that perennial crops can be part of the solution, especially on sandy soils, where challenges are greatest.”
Mere information
Collaborators: Department of Agroecology, Aarhus University and Thünen Institute of Climate-Smart Agriculture.
Funding:This work was funded by the Aarhus University Research Foundation (AUFF-E-2019–7-1), and GrassTools (Innovation Fund Denmark, NO. 0224-00091B). MZ was funded by the China Scholarship Council (CSC NO. 202107030005) for studying at Aarhus University. LE and ZL were financially supported by the EJPSoil project CarboSeq, which has received funding from the European Union's Horizon 2020 research and innovation programme (grant agreement No. 862695). DA was supported by the Danish Council for Independent Research (DFF-1 Grant No. 9041–00324B, and DFF-Sapere Aude Grant No. 1051–00060B).
Conflict of interest: None
Read more: The publication "Ten-year effects of perennial cropping systems on soil organic carbon stock and stability in sandy soils: Mechanisms and biochemical drivers" is published in European Journal of Agronomy. It is written by Mingming Zong, Diego Abalos, Ji CHen, Zhi Liang, Yue Li, Lars Elsgaard, Christopher Poeplau, Marcus Schiedung and Uffe Jørgensen.
Contact: Mingmin Zong, Department of Agroecology, Aarhus University. Mail: mingming.zong@agro.au.dk