Characterization of soil amendment potential of 18 different biochar types produced by slow pyrolysis

Abstract

Feedstock type is the most dominant factor influencing the physical characteristics and chemical composition of biochar. The main purpose of this study was to characterize and compare some of the physical and chemical properties of biochars produced by slow pyrolysis of 18 feedstocks, which are locally available agricultural residues. Moreover, elucidating the potential agronomic benefits of these biochars was the other objective of the study. Biochars were produced at 500 oC in an ingeniously developed reactor. The biochars were characterized for specific surface area (SSA), field capacity (FC), wilting point (WP), plant available water content (AW), pH, electrical conductivity (EC), cation exchange capacity (CEC), total carbon (C) and nitrogen (N), plant available phosphorus (P) and potassium (K) concentrations. Considerable variation of characteristics among biochars indicates the dominant impact of feedstock type on physical properties and chemical composition of biochars. Total C contents were highly variable with values up to 91.9% for pine sawdust. Phosphorus and K in feedstocks were concentrated in the biochars and were two to four times higher in the biochars. The CEC of biochars varied from 79.5 cmol kg-1 (pepper residues) to 5.77 cmol kg-1 (poplar sawdust). The CEC and SSA had a significant negative correlation (P<0.01, r= -0.70) that probably be attributed to the loss of functional groups during pyrolysis. The results revealed that depending on the feedstock, some biochars have potential to serve as nutrient sources as well as an additive to improve soil quality.

Keywords

• Agricultural residues
• feedstock type
• biochar
• physical and chemical properties
• soil quality.