Effect of Pyrolysis Temperature and Feedstock Type on Agricultural Properties and Stability of Biochars

Pyrolysis temperature and feedstock type used to produce biochar influence the physicochemical properties of the obtained product, which in turn display a range of results when used as soil amendment. From soil carbon (C) sequestration strategy to nutrient source, biochar is used to enhance soil properties and to improve agricultural production. However, contrasting effects are observed from biochar application to soil results from a wide range of biochar’s properties in combination with specific environmental conditions. Therefore, elucidation on the effect of pyrolysis conditions and feedstock type on biochar properties may provide basic information to the understanding of soil and biochar interactions. In this study, biochar was produced from four different agricultural organic residues: Poultry litter, sugarcane straw, rice hull and sawdust pyrolysed at final temperatures of 350°C, 450°C, 550°C and 650°C. The effect of temperature and feedstock type on the variability of physicochemical properties of biochars was evaluated through measurements of pH, electrical conductivity, cation exchange capacity, macronutrient content, proximate and elemental analyses, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyses. Additionally, an incubation trial was carried under controlled conditions to determine the effect of biochar stability on CO2-eq emissions. Results showed that increasing pyrolysis temperature supported biochar stability regardless of feedstock, however, agricultural properties varied widely both as an effect of temperature and feedstock. Animal manure biochar showed higher potential as nutrient source rather than a C sequestration strategy. Improving the knowledge on the influence of pyrolysis temperature and feedstock type on the final properties of biochar will enable the use of better tailored materials that correspond to the expected results while considering its interactions with environmental conditions.