Bone biochar and humic acid show strong potential to restore coastal saline soils and boost olive tree growth
image: Bone biochar and humic acid improved soil quality and promoted Olea europaea growth in coastal saline soil by enhancing the stoichiometric homeostasis of nutrient elements
Credit: Weibin Zhao, Jiang Xiao, Shufeng Wang, Xu Gai & Guangcai Chen
Researchers in China have discovered that a combination of bone biochar and humic acid can dramatically improve coastal saline soils and help olive trees thrive in these challenging environments. The study, published in Biochar, uncovers how these soil amendments work together to enhance soil structure, rebalance essential nutrients, and support healthy plant growth.
“Soil salinisation is one of the most serious threats to agriculture worldwide,” said lead author Weibin Zhao of the Research Institute of Subtropical Forestry, Chinese Academy of Forestry. “Our findings show that a simple and low cost combination of bone biochar and humic acid can greatly improve soil quality and help olive trees grow stronger in saline coastal regions.”
Coastal saline soils are often marked by excessive sodium, nutrient loss, poor structure, and low microbial activity. These conditions inhibit plant growth and limit crop production. The research team tested whether two common soil amendments, bone biochar (a carbon rich material made from pyrolyzed animal bone) and humic acid (a natural organic compound), could improve both soil health and plant performance when applied together.
The team grew two year old olive seedlings (Olea europaea L.) in coastal saline soil under greenhouse conditions and compared seven treatments. These included low and high application rates of bone biochar, humic acid, their combination, and a control without amendments. The combined treatment at five percent by volume provided the strongest benefits.
According to the study, the combined amendments significantly increased soil porosity and reduced sodium content by up to sixty six percent. Soil enzyme activities and nutrient levels also improved, especially for organic carbon, nitrogen, and essential cations. These improvements created a healthier soil environment that allowed olive trees to absorb more potassium, calcium, and magnesium while taking up less sodium.
“We observed clear improvements in soil structure and nutrient availability after adding bone biochar and humic acid together,” said co author Shufeng Wang. “Better soil conditions directly supported stronger plant growth and higher nutrient balance in the olive seedlings.”
The olive trees showed notable gains in height, root length, biomass, and photosynthetic activity. Chlorophyll content increased by more than twenty percent, while gas exchange indicators such as transpiration rate also rose. Levels of harmful oxidative stress markers declined, and antioxidant enzyme activities increased, suggesting that the amendments helped olive trees tolerate saline stress more effectively.
A key insight from the study involves nutrient stoichiometry. Healthy plant growth requires a stable internal balance of carbon, nitrogen, and phosphorus. The researchers found that the combined amendments strengthened this stoichiometric homeostasis in olive plants, indicating better regulation of nutrient uptake and internal nutrient stability. Structural equation modeling further confirmed that improved stoichiometric balance and enhanced soil quality directly contributed to stronger plant growth.
“Our analysis showed that the amendments not only improved soil conditions but also helped the olive trees maintain more stable nutrient levels,” said senior author Guangcai Chen. “This stability is critical for long term growth in stressful saline environments.”
Because bone biochar can be produced from agricultural waste and humic acid is an affordable organic fertilizer, the researchers say that these amendments offer a practical strategy for large scale restoration of saline and alkali affected coastal land. Olive trees, valued both as a cash crop and as a species suitable for coastal shelterbelts, may be especially promising for such regions.
The team notes that their findings are based on greenhouse experiments and encourages long term field trials to confirm real world performance. Still, the results highlight a promising path toward sustainable soil management in coastal regions facing increasing salt intrusion and land degradation.
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Journal Reference: Zhao, W., Xiao, J., Wang, S. et al. Bone biochar and humic acid improved soil quality and promoted Olea europaea growth in coastal saline soil by enhancing the stoichiometric homeostasis of nutrient elements. Biochar 7, 70 (2025).
https://doi.org/10.1007/s42773-025-00461-3
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About Biochar
Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.