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 degrees C, 400 degrees C, 500 degrees C and 700 degrees 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 degrees C showed high hydrophobity, which disappeared over 500 degrees C owing to the loss of labile aliphatic compounds. The high pH and carbonates contents at >500 degrees C resulted in suitable biochars for soil liming and decreasing soil metals availability.(c) 2015 Elsevier Ltd. All rights reserved.