Designer, acidic biochar influences calcareous soil characteristics

An acidic (pH 5.8) biochar was created using a low pyrolysis temperature (350 degrees celsius) and steam activation to potentially improve the soil physicochemical status of an eroded calcareous soil. Biochar was added at 0, 1, 2, and 10 percent (by weight) to an eroded Portneuf soil (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) and destructively sampled at 1, 2, 3, 4, 5, and 6 month intervals. Soil was analyzed for volumetric water content, pH, nitrate-nitrogen, ammonium-nitrogen, plant-available iron, zinc, manganese, copper, and phosphorus, organic carbon, carbon dioxide respiration, and microbial enumeration via extractable DNA and 16S rRNA gene copies. Soil water content increased with biochar application regardless of rate; the response was consistent over time. Soil pH decreased between 0.2 and 0.4 units, while plant-available zinc, manganese, and phosphorus increased with increasing biochar application rate. Micronutrient availability tended to decrease over time likely due to the precipitation of insoluble mineral species. Increasing biochar application raised the soil organic carbon content and it remained elevated over time. Increasing biochar application rate also increased respired carbon dioxide, yet the carbon dioxide released decreased over time. Soil nitrate-nitrogen concentrations significantly decreased with increasing biochar application rate likely due to microbial immobilization. Depending on application rate, biochar produced a 1.4 to 2.1-fold increase in soil DNA extracted and 1.4- to 2.4-fold increase in 16S rRNA gene abundance over control soils, suggesting microbial stimulation and a subsequent burst of activity upon biochar addition. Our results showed that there is promise in designing a biochar to improve the quality of eroded calcareous soils with concomitant increases in soil microbial activity