title: Nitrate capture and slow release in biochar amended compost and soil.
abstract: Slow release of nitrate by charred organic matter used as a soil amendment (i.e. biochar) was recently suggested as potential mechanism of nutrient delivery to plants which may explain some agronomic benefits of biochar. So far, isolated soil-aged and composted biochar particles were shown to release considerable amounts of nitrate only in extended (>1 h) extractions ("slow release"). In this study, we quantified nitrate and ammonium release by biochar-amended soil and compost during up to 167 h of repeated extractions in up to six consecutive steps to determine the effect of biochar on the overall mineral nitrogen retention. We used composts produced from mixed manures amended with three contrasting biochars prior to aerobic composting and a loamy soil that was amended with biochar three years prior to analysis and compared both to non-biochar amended controls. Composts were extracted with 2 M KCl at 22°C and 65°C, after sterilization, after treatment with H2O2, after removing biochar particles or without any modification. Soils were extracted with 2 M KCl at 22°C. Ammonium was continuously released during the extractions, independent of biochar amendment and is probably the result of abiotic ammonification. For the pure compost, nitrate extraction was complete after 1 h, while from biochar-amended composts, up to 30% of total nitrate extracted was only released during subsequent extraction steps. The loamy soil released 70% of its total nitrate amount in subsequent extractions, the biochar-amended soil 58%. However, biochar amendment doubled the amount of total extractable nitrate. Thus, biochar nitrate capture can be a relevant contribution to the overall nitrate retention in agroecosystems. Our results also indicate that the total nitrate amount in biochar amended soils and composts may frequently be underestimated. Furthermore, biochars could prevent nitrate loss from agroecosystems and may be developed into slow-release fertilizers to reduce global N fertilizer demands.
authors.affiliation: Geomicrobiology, Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, Tuebingen, Germany.
authors.forename: Nikolas
authors.identifier: http://orcid.org/0000-0001-8005-9392
authors.initials: N
authors.lastname: Hagemann
authors.affiliation: Working group Climate Change Research for Special Crops, Department for Soil Science and Plant Nutrition, Hochschule Geisenheim University, Geisenheim, Germany.
authors.forename: Claudia I
authors.initials: CI
authors.lastname: Kammann
authors.affiliation: Ithaka Institute for Carbon Strategies, Ancienne Eglise 9, Arbaz, Switzerland.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Schmidt
authors.affiliation: Geomicrobiology, Center for Applied Geoscience, University of Tuebingen, Sigwartstrasse 10, Tuebingen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kappler
authors.affiliation: Department for Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, MN, United States of America.|BioTechonology Institute, 140 Gortner Labs, 1479 Gortner Avenue, St. Paul, Mn, United States of America.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Behrens
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis; D002606:Charcoal / Q000737:chemistry*; D005308:Fertilizers / Q000032:analysis; D006861:Hydrogen Peroxide / Q000737:chemistry; D009566:Nitrates / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D013242:Sterilization; D013696:Temperature; D013997:Time Factors
chemical_list: D064751:Ammonium Compounds; D005308:Fertilizers; D009566:Nitrates; D012987:Soil; C540010:biochar; D002606:Charcoal; D006861:Hydrogen Peroxide