Nutrient release from switchgrass-derived biochar pellets embedded with fertilizers

- Pellets with high lignin% and temperature had high durability low functionality.
- Pellets with high lignin% and temperature had small pore size and low porosity.
- Pellets with high lignin% and temperature had slow water uptake slop over time.
- Increasing lignin content in the pellets reduced nutrient release rate over time.
- Pellets processed at 180 °C had slower nutrient release than pellets at 105 °C.

Biochar pellets produced by blending switchgrass biochar, lignin and fertilizers K and P together followed by pelletization were characterized and investigated for their ability to release K and P. Pellets processed at 180 °C with increasing lignin content from 10 to 30 wt.% had higher density, thermal stability and durability, and produced lower pore volume and smaller pore size than pellets processed at 105 °C. Fertilizer-embedded biochar pellets with 10-30 wt.% lignin and processed at 180 °C had a slower K and P release than pellets dried at 105 °C, with release rates (53-62% in K and 49-62% in P) within the first 24 h followed by gradual releases (78-87% in K and 73-78% in P) for the next 18 days. Therefore, by controlling lignin content and processing temperature of the pellets, one can control the release rate of nutrients present in biochar pellets.