Scientists have analyzed whether planting turf and clover beneath solar panels can increase soil organic carbon, after measuring the results from a commercial plant in Japan. They tested more than 20 areas in the power plant and found that soil organic carbon increased.
Researchers from Kyushu University in Japan have studied whether planting turf and clover beneath solar panels can increase soil organic carbon (SOC).
“This research is novel by establishing a scientific basis for potential carbon credits,” highlighted corresponding author Michiyuki Yagi in a conversation with pv magazine.
The scientists planted seeds under panels in a commercial plant, and measured SOC content in the soil with three different methods. “SOC is a particularly promising natural climate solutions (NCS) component with substantial mitigation potential,” they explained. “The carbon cycle involves interactions among the atmosphere, soil, and plants. Plants absorb CO₂ via photosynthesis, then contribute to SOC through residues that soil microbes decompose, releasing CO₂ back to the atmosphere.”
The measurements were carried out in a solar park in Akaiwa, Okayama prefecture, Japan, operational since 2021. A total area of 494,773.18 m² under the solar panels was covered with turf and clover using a spray-based method. Fertilizers, seeds, and fibers were mixed in a solution to prevent erosion. Three measurement methods were applied on three sites: loss on ignition (LOI), Tyurin and the total organic carbon (TOC) meter method.
Image: Kyushu University, Environmental Challenges, CC BY 4.0
While the LOI method estimates organic carbon by burning soil and measuring weight loss, Tyurin uses chemical reactions to oxidize carbon and titration to measure it, and TOC directly measures CO₂ from burned soil. “We were surprised by the significant variability in SOC measurements among different methods. LOI and the Tyurin method yielded similar results, which differed markedly from those obtained via automated dry combustion using TOC meters,” added Professor Yagi.
Based on that, the researchers decided to focus on the LOI method, and have used it to measure 21 further soil sites across the test site. “Although the LOI method proved practical, employing more precise techniques (e.g., automated dry combustion) and including deeper soil layers would strengthen future assessments,” the group highlighted.
According to the results from all of the measured sites, the SOC at the Okayama project had an annual increase of about 0.927 tC/ha (3.397 tCO₂e/ha), leading to net GHG removals of 85.8 tCO₂e over two years. The team further suggests that well-managed under-panel vegetation could continue to yield annual reductions of about 168.1 tCO₂e.
“By integrating renewable energy infrastructure with vegetation-based carbon removal, this approach offers a promising avenue for emissions mitigation and carbon credit generation. It can complement ongoing efforts in forest management, particularly in areas where steep terrain or fragmented ownership limits new tree planting,” the team concluded. “Continued research and broader adoption of standardized measurement methods may help Japan develop a more robust voluntary carbon market and advance overall decarbonization goals under its unique geographic constraints.”
The experiment was described in detail in “Soil organic carbon credits from turf and clover planting beneath solar panels,” published in Environmental Challenges.