Nitrate capture and slow release in biochar amended compost and soil.

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PloS one, ISSN: 1932-6203, Vol: 12, Issue: 2, Page: e0171214

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10.1371/journal.pone.0171214; 10.1371/journal.pone.0171214.t002; 10.1371/journal.pone.0171214.g001; 10.1371/journal.pone.0171214.g002; 10.1371/journal.pone.0171214.g003; 10.1371/journal.pone.0171214.t001
Nikolas Hagemann; Claudia I. Kammann; Hans-Peter Schmidt; Andreas Kappler; Sebastian Behrens; Jorge Paz-Ferreiro
Public Library of Science (PLoS); Figshare
Biochemistry, Genetics and Molecular Biology; Agricultural and Biological Sciences; Space Science; Microbiology; Molecular Biology; Environmental Sciences not elsewhere classified; Chemical Sciences not elsewhere classified; Ecology; Biological Sciences not elsewhere classified; Plant Biology; 2 M KCl; release; loamy soil; N fertilizer demands; nitrate amount; biochar amendment; extraction; H 2 O 2; composted biochar particles; mineral nitrogen retention; 59999 Environmental Sciences not elsewhere classified; 69999 Biological Sciences not elsewhere classified; 39999 Chemical Sciences not elsewhere classified
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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.