FRANKFORT, Ky. – According to Kentucky State University (KSU) researchers, a two-year field study of pine sawdust biochar is offering a promising soil management strategy for addressing two long-term challenges in soybean production: soil acidification and declining soil organic carbon.

The study evaluated pine sawdust biochar in acidic silt loam soils under continuous soybean cultivation. Biochar is a charcoal-like, carbon-rich material produced by heating wood or other plant matter in an environment with very little or no oxygen.

Researchers applied biochar at 12 tons per hectare each year, incorporating it into the top 15 centimeters of soil before planting. According to KSU, a hectare is a metric unit of area equal to roughly 2.47 acres.

Soil samples were collected before planting and after harvest to assess acidity, organic reserves, fertility and hydrological (the study of water on the Earth) properties. After two years, biochar-treated plots maintained higher post-harvest soil pH, and increased soil organic carbon from 1.74 percent to 1.96 percent.

Conducted by Binaya Baral under the mentorship of Anuj Chiluwal, KSU assistant professor of agronomy, at KSU’s Harold R. Benson Research and Demonstration Farm, the study said acidic soils can limit soybean growth by reducing nutrient availability, and interfering with biological nitrogen fixation: “Our research shows that biochar can help buffer soil acidity and improve soil carbon over time,” Baral said. Nitrogen fixation is the study of how soil fertility, supplemental nitrogen, and biochar influence crop productivity and sustainability, according to KSU.

Baral published the findings as first author in the peer-reviewed paper, “Response to acidic silt loam soil properties to biochar application under soybean cultivation,” with Chiluwal serving as the corresponding author. Baral is now a graduate research assistant and doctoral student in the University of Florida Department of Agricultural and Biological Engineering.

His current research focuses on best management practices-based sod rotation and integrated crop-livestock systems to improve nutrient management, reduce nitrogen leaching, and sustain crop productivity in Florida’s sandy soils.

Co-authors include Deepak Khatri, former KSU research associate in agronomy; Sudip Poudel, KSU research associate in crop physiology; Lalit Pun Magar, former KSU research associate in precision agriculture; and Atanu Mukherjee, a former KSU faculty member.

Chiluwal said the findings show biochar’s value as a long-term soil amendment rather than an immediate fertilizer replacement, adding that future multi-rate studies are needed to identify practical and cost-effective application rates. KSU researchers said a soil amendment is any organic, physical or chemical material added to soil to modify and improve its properties.

“Interest in biochar as a sustainable soil amendment is increasing,” Chiluwal told Farm World. “However, most existing research has focused on its effects in degraded soils, while its impacts on fertile agricultural soils remain underexplored. Therefore, this study evaluated the effects of pine sawdust biochar application on the properties of fertile silty loam soil in Kentucky.”

He said even productive agricultural soils can gradually degrade under continuous cultivation, highlighting the need for sustainable practices to maintain soil health and productivity, which is beneficial to farmers.

“In our study, pine sawdust biochar did not significantly affect most measured soil health parameters under continuous soybean production over the medium term,” he said. “However, it reduced soil acidity and increased soil organic carbon two years after application, while biologically active carbon and manganese increased three years after application,” he added.

The study is part of ongoing research supported by the USDA-National Institute of Food and Agriculture 1890 Capacity Building Grant to KSU: “We will continue this study to better understand the long-term effects of biochar, and provide more definitive results on its potential to maintain soil health in fertile agricultural soils,” Chiluwal said.