Optimizing biochar application: Effects of placement method, particle size, and application rate on soil physical properties and soil loss

The objective of this research was to examine the influence of olive kernel biochar on silty clay soil that is susceptible to erosion. The hypothesis proposed that the effectiveness of biochar in improving soil physical properties and mitigating soil erosion depends on factors such as application rate, particle size as well as placement method.

Three application rates (0, 1, and 2%) and two particle size ranges (53–250 and 250–500 µm) of biochar were tested, along with two placement methods (commixing and slurry). Effects of biochar application on soil aggregate stability and water repellency were investigated after a 10-month incubation period. Effectiveness of biochar to reduce soil loss and runoff generation was also assessed.

The biochar application resulted in a reduction of soil water repellency. Notably, regarding particle size, application rate, and placement method, no statistically significant difference was observed. The slurry method resulted in about 30% higher mean weight diameter of aggregate (MWD) compared to the commixing. The reduced soil disturbance in the slurry method may allow for greater enhancement of soil aggregation by biochar. The relative decrease in runoff (462 vs. 356%) and soil loss (52 vs. 23%) in biochar-treated soils compared to the control treatment were considerably higher in the slurry than commix method. The results also demonstrated a significant interaction between the biochar placement method and treatment type regarding soil loss characteristics in both commixing and slurry methods. Larger biochar particles at higher rates effectively reduced runoff and soil loss using the slurry method, while smaller biochar particles at lower rates were more effective with commixing method.

Overall, the slurry method proved effective in incorporating biochar into erosion-prone areas. Furthermore, the selection of appropriate biochar particle sizes and application rates is crucial for optimizing desired outcomes.