Agronomic Practices Emerge as The Real Key to Carbon-Neutral Olive Groves

Research conducted in Portuguese olive groves found that soil carbon inputs, cover crops and pruning residues mattered more than organic certification labels for improving the carbon balance of groves.

A lot can be achieved by better managing the carbon that is already produced inside the olive grove.– Evangelina Pareja Sánchez, Researcher, University of Jaén

A study published in Environmental Research Communications examined six olive groves in Portugal’s Alentejo region managed under integrated, organic and biodynamic-organic systems.

Researchers found that farms with high annual carbon inputs consistently achieved positive carbon balances, regardless of whether they were organic, biodynamic or integrated. Low-input systems showed far more variable outcomes, including net carbon losses.

In the study, “high-input” groves were farms that returned larger amounts of organic matter to the soil through practices such as cover crops, pruning residues and organic amendments, while “low-input” systems returned much smaller quantities of biomass and carbon to the soil each year.

The study found that net emissions fell to around 140 kilograms of carbon dioxide equivalent per hectare annually in high-input groves, compared to about 1,650 kilograms in low-input systems.

The findings suggest Mediterranean olive groves may be capable of approaching carbon neutrality and that the key factor is how much organic carbon is returned to the soil each year.

“Farms with low carbon inputs sometimes did not provide enough organic material to balance the natural carbon losses from the soil, and this explains why some of them showed negative carbon balances,” Evangelina Pareja Sánchez, post-doctoral researcher at the University of Jaén in Spain and co-author of the study, told Olive Oil Times.

Olive groves continuously lose carbon through natural and human-driven processes. Soil microorganisms break down organic matter and release carbon dioxide back into the atmosphere through soil respiration, while erosion can remove carbon-rich topsoil during heavy rainfall events.

Additional emissions are generated by farming activities such as the use of machinery, irrigation, fertilization and tillage.

The highest-performing groves reached positive carbon balances of about 1 metric ton of carbon per hectare annually, meaning they stored more carbon in soil and tree biomass than they released into the atmosphere each year.

“The main factor was the amount of organic carbon entering the soil every year,” Pareja-Sánchez explained.

Cover crops, increasingly used in olive groves across the Mediterranean basin, proved to be one of the most effective tools for enhancing carbon sequestration.

“Cover crops were especially important because they provide both aboveground biomass and root biomass, helping to feed the soil continuously,” the researcher said.

According to the study, spontaneous cover crops accounted for between 42 and 51 percent of total carbon inputs in the olive groves analyzed.

Pruning residues also proved significant. While some growers still remove wood and branches from orchards after pruning, the study found that this carbon-rich material can instead be chipped and reincorporated into the soil.

“These practices not only contribute to carbon sequestration but also improve soil structure, reduce erosion and increase water retention, which is particularly important under Mediterranean conditions,” Pareja-Sánchez said, referring to the growing challenges associated with a rapidly changing climate.

The research was conducted in Portugal’s Alentejo region, one of the country’s most important olive-growing areas and a region that has undergone rapid agricultural intensification in recent decades.

The findings challenge the assumption that certification systems alone determine environmental performance.

“What really mattered was how much organic matter was returned to the system each year,” Pareja-Sánchez said.

The researchers emphasized that many of the most effective carbon-sequestering practices do not necessarily require major external investments.

“The key message is that farmers do not always need to bring in large amounts of external material,” Pareja-Sánchez said. “A lot can be achieved by better managing the carbon that is already produced inside the olive grove.”

The role of olive groves as potential carbon sinks is receiving increasing attention through European Union carbon farming initiatives and projects such as the International Olive Council’s Carbon Balance project.

Olive groves and other agricultural soils are increasingly viewed as potential carbon sinks that can partially offset greenhouse gas emissions while improving long-term soil resilience.

The study found that emissions from farming operations were similar across systems, averaging 3,200 to 3,400 kilograms of carbon dioxide equivalent per hectare annually.

According to the researchers, extrapolating the findings to Portugal’s roughly 400,000 hectares of olive groves suggests the sector could sequester approximately 0.58 million metric tons of carbon dioxide annually through carbon stored in tree biomass alone.

The study also estimated that the annual biomass accumulated by olive trees could offset emissions equivalent to 310,000 to 438,000 tons of carbon dioxide per year.

At the same time, the authors cautioned against portraying olive groves as a permanent climate solution.

“Soil carbon sequestration is not an infinite process,” Pareja-Sánchez said. “When sustainable practices are introduced, soils can accumulate carbon for a certain period, but over time they tend to approach a new equilibrium.”

As soils become richer in organic carbon, the rate of accumulation gradually slows, meaning soils cannot continue storing carbon indefinitely at the same pace.

“In the long term, carbon sequestration needs to be combined with reductions in greenhouse gas emissions from farming operations, for example by optimizing fertilization, reducing unnecessary tillage and improving energy efficiency,” Pareja-Sánchez said.

Although the research focused on Alentejo, the authors believe the broader conclusions are relevant across Mediterranean olive-growing regions facing similar environmental pressures.

“Many Mediterranean areas share similar challenges: low soil organic matter, summer drought, erosion risk and increasing pressure to maintain productivity while reducing environmental impacts,” Pareja-Sánchez said. “Therefore, the principle that increasing organic carbon inputs improves carbon balance is likely applicable beyond Portugal.”

The study also explored differences between traditional olive groves and modern intensive systems, a topic of increasing debate as super-high-density plantations continue to expand in parts of the Mediterranean basin.

According to the researchers, intensive systems generally generate higher emissions because they require more irrigation, machinery use and external inputs. However, they may still achieve positive carbon balances if they maintain sufficient vegetation cover and biomass recycling.

“Traditional olive groves, especially when they have permanent or spontaneous cover and low soil disturbance, can also have strong potential for carbon sequestration,” Pareja-Sánchez said. “In our study, the most important factor was not the production model itself, but the balance between carbon inputs and carbon losses.”

The researcher added that both traditional and intensive groves can contribute to climate mitigation if managed to increase soil organic matter while minimizing unnecessary losses.

“The challenge is to adapt sustainable practices to each type of olive grove,” she concluded.