Coastal saline soils, often found in buffer zones between land and sea, present a major challenge for agriculture due to high salt content, poor permeability, and low nutrient levels. These conditions lead to low productivity and inefficient land use, which is a growing problem in coastal areas with land scarcity. A recent study published in the journal Agronomy by Wenzhi Zhou and a team of researchers from institutions including the Chinese Academy of Forestry and Beijing Forestry University, explored how amending these soils with biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More and compost could improve their quality. The researchers found that these amendments not only reduce salinity but also improve the physical and biological properties of the soil.

Biochar is widely used as a soil conditioner because its porous structure and large surface area can improve soil permeability and reduce bulk density. In saline soils, biochar’s positively charged ions like calcium (Ca2+) and magnesium (Mg2+) can replace sodium (Na+) adsorbed by soil particles, which helps lower the sodium adsorption ratio (SAR). Similarly, compost, a carbon-rich and loose-textured material, can be used to improve soil structure, fertility, and microbial activity. The organic matter in compost helps soil particles bind together, promoting the formation of stable aggregates.

In a series of lab experiments, the research team investigated the effects of biochar, compost, and a combination of both on coastal saline soil from Dongying City, China. They conducted leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More tests and nine-month soil culture experiments using varying application rates. They found that applying biochar alone initially increased the pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More of the leaching solution due to its naturally alkaline nature. However, compost, which contains organic acids and has a high cation exchange capacity, effectively lowered the soil pH. When biochar and compost were applied together, they had a complementary effect on soil pH.

The most significant results were seen in the soil’s salinity and physical properties. In leaching tests, treatments with amendments had a faster salt elution rate compared to the control group. The combined biochar and compost treatment (BW) showed the fastest salt leaching rate. At the end of the leaching experiment, the combined treatment reduced the soil’s electrical conductivity (EC) by 51.22% and the SAR by 63.82% compared to the control group.

The soil culture tests confirmed these findings, showing that the combined application of biochar and compost significantly improved soil physical properties. The optimal application rate, which resulted in the lowest EC value, was 10 g/kg of biochar and 40 g/kg of compost. This treatment also increased the saturated hydraulic conductivity by an impressive 351.7% compared to the unamended soil, indicating a dramatic improvement in water flow and drainage. The researchers noted that while biochar alone didn’t significantly affect soil aggregate stability, compost applications did, and the combination further enhanced this effect.

Beyond physical improvements, the study also found that the amendments increased soil nutrients and enzyme activity. Both biochar and compost are rich in key nutrients like nitrogen, phosphorus, and potassium, which become more available to the soil through microbial decomposition. The application of both materials led to significant increases in soil organic matter and the activity of enzymes like urease and phosphatase. However, the researchers cautioned that excessively high application rates of biochar could increase soil pH, and too much compost could raise soil conductivity, negatively affecting enzyme activity. This highlights the importance of carefully controlling application rates to achieve the best results.

Overall, the findings suggest that the combined use of biochar and compost is a highly effective strategy for rehabilitating coastal saline soils. The study provides a clear theoretical basis for improving coastal saline soils, demonstrating how these amendments work together to lower salinity, improve physical structure, and enhance nutrient availability. Future research should focus on the synergistic effects of biochar and compost to further optimize their application for large-scale soil improvement.

Source: Zhou, W., Xing, S., Wu, Y., Zou, R., Li, S., Sun, X., & Zhang, H. (2025). Exploring the Effects of Biochar and Compost on Ameliorating Coastal Saline Soil. Agronomy, 15(9), 2093.