Stability, nutrient availability and hydrophobicity of biochars derived from manure, crop residues, and municipal solid waste for their use as soil amendments.

We aimed to study the influence of feedstock properties, pyrolysis temperature and holding time on stability, nutrient contents and hydrophobicity of biochars derived from pig manure, crop residues and municipal solid waste. Biochars were prepared at 300 °C, 400 °C, 500 °C and 700 °C for 1 h, 2 h, 4 h and 5 h. All properties were influenced by feedstock except for pH and hydrophobicity. Temperature influenced all properties, whereas no effect of holding time was observed except for hydrophobicity and thermal stability. Increasing temperature increased aromatization and stability. Low temperatures provided higher cation exchange capacity and available nutrients, and lower salinity and alkalinity. Precipitation of phosphates and carbonates occurred with charring, explaining the decrease of available nutrients. Biochars produced at 300 °C showed high hydrophobity, which disappeared over 500 °C owing to the loss of labile aliphatic compounds. The high pH and carbonates contents at >500 °C resulted in suitable biochars for soil liming and decreasing soil metals availability.