Chemical and bioassay characterisation of nitrogen availability in biochar produced from dairy manure and biosolids

• Published in: Organic geochemistry Vol. 51; pp. 45 - 54
• Main Authors: Wang, Tao, Camps Arbestain, Marta, Hedley, Mike, Bishop, Peter
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.2012; Elsevier
• Subjects: amino acids; amino sugars; ammonium nitrogen; bioassays; biochar; biomass; biosolids; carbon; carbon dioxide; dairy manure; Earth and Related Environmental Sciences; Earth sciences; Earth, ocean, space; emissions; Engineering and environment geology. Geothermics; Eucalyptus; Exact sciences and technology; fractionation; Geochemistry; Geovetenskap och miljövetenskap; Geovetenskap och relaterad miljövetenskap; heat; humans; hydrochloric acid; hydrolysis; mineralization; Natural Sciences; Naturvetenskap; nitrogen; oxidation; Pollution, environment geology; pyrolysis; sand; sodium hydroxide; soil; Soil and rock geochemistry; Soils; Surficial geology; temperature; wood chips; carbon dioxide; fractionation; biomass; sugars; nitrogen; amino acids; streams; liquid waste; oxidation; degradation; indicators; pollution; sand; pyrolysis; carbon; solid waste; temperature; wood; charcoal; soils; hydrolysis; volatiles
• ISSN: 0146-6380; 1873-5290; 1873-5290
• DOI: 10.1016/j.orggeochem.2012.07.009

► 6M HCl acid hydrolysable forms of N in biochar were investigated. ► Influence of pyrolysis temperature on these forms also investigated. ► C and N cycling in biochar from different pyrolysis temperatures were studied. ► Modified C/N ratio for estimating net N mineralisation in biochar was proposed. ► Extraction of N with 6M HCl could be used to estimate labile N in biochar. Biochar is charcoal made from waste biomass and intended to be added to soil to improve soil function and reduce emissions from the biomass caused by natural degradation to CO2. Nitrogen (N) forms in biochar can be complex and their lability likely to be influenced by pyrolysis temperature which, together with the nature of carbon (C), will influence N mineralisation or immobilisation. These complex relationships are poorly understood, yet impact strongly on the potential agronomic value of biochar. In this study, N in different biochar samples produced from human and animal waste streams (biosolids and cow manure; each mixed with eucalyptus wood chips in a 1:1 dry wt. ratio) at different pyrolysis conditions (highest heating temperature 250, 350, 450 and 550°C) was extracted with 6M HCl. The acid hydrolysable, extractable N (THN) was fractionated into ammonia N (AN), amino acid N (AAN), amino sugar N (ASN) and uncharacterisable hydrolysable N (UHN). Biochar samples were also treated with 0.167M K2Cr2O7 acid to determine N potentially available in the long term. An incubation study of the different biochar samples mixed with acid washed sand was conducted at 32°C for 81 days to study both C and N turnover. During incubation, the CO2 released was trapped in NaOH and quantified. Hydrolysable N decreased as pyrolysis temperature increased from 250 to 550°C. Fractionation into AN, AAN, ASN and UHN revealed progressive structural rearrangement of N with pyrolysis temperature. Based on HCl hydrolysis and dichromate oxidation results, C and N in biochar became more stable as pyrolysis temperature increased. The ratio of volatile C to THN was a useful indicator of whether net N mineralisation or immobilisation of N in biochar occurred. THN thus seems a sound estimate of the labile N fraction in biochar in the short term; however, dichromate-oxidisable N is probably more meaningful in the long run. Further studies using different types of biochar need to be conducted under more realistic conditions to obtain more information on N availability in biochar once in soil.