CO2-Binding of ammonoxidized lignins and their use as soil improvers (COBAL)
Final Report Abstract
Lignin is a major by-product of the pulp and paper industry.The goal of the present project was to test if ammonoxidized lignins can be transformed into a value-added product and used as a soil amendment. Considering the complex binding forms of N with different hydrolysis rates, it was hypothized that they could be used as slow-release N fertilizer. Based on the observation that ammonoxidized methoxyhydroquinone and 2,5-dihydroxy-[1,4]benzoquinone bind CO2, we hypothized that N-lignins may add to C-sequestration in amended soils. Thus, they may reduce the amount of anthropogenic organic waste and concomitantly improve soil quality and the size of the slow turning soil organic C pool. Additionally, we expected an increase of the N- fertilization efficiency combined with a reduction of the negative environmental impact encountered with the application of mineral N fertilizers. In our study, we combined an improved chemical characterization of ammonoxidized ligneous matter and their CO2-binding potential, with laboratory pot experiments, performed to evaluate their behavior and stability during the biochemical reworking in biologically active soils. Whereas the chemical characterization of the N-lignins was achieved by the Austrian partner, the latter was the main focus of the German group and performed by adding 15N-lignins supplied by the Austrian partner, both to material from a Tierrra rossa (a typical Spanish agriculturally used site) and from a Luvisol (derived from the experimental station Viehhausen of the TU-München). For comparison, pots were incubated with K15NO3 and 15N-enriched plant char, as an alternative slow-release N fertilizer. The 15N-enrichment allowed the study of the distribution of added N in the soil and its uptake by the plants as well as the determination of the 15N partitioning into microbial biomass (fumigation-extraction method). The chemical transformation of the N-forms in the soil was examined by solid-state 15N NMR spectroscopy. Compared to pots amended with mineral N (K15NO3) or N-rich 15N-plant char, the addition of N- lignins showed an improved fertilization only during the second part of the 2 month incubation. Addition above 1 g N via N-lignin retarded the germination. In contrast to our expectation, solidstate 15N NMR spectra of the soil at different incubation times revealed a fast N-transformation into peptide-like compounds. This was in line with the quick recovery of added 15N in the microbial biomass already during the first weeks of the experiment and points to lower biochemical stability of aromatic N-structures than commonly assumed. Thus, the potential of N- lignins as a slow-release N fertilizer seems to be caused rather by N-immobilization into microbial biomass than by stepwise release due to different hydrolysis rates. The harvested plants showed an N enrichment caused by the amendment. Respiration experiments revealed comparable CO2 production rates in soil incubated with and without N-lignins. In summary, our study confirmed that at least some N-lignins can contribute to a sequestration of N in soils, although this is mostly due to microbial activity and a fast incorporation of N-lignin derived N into their biomass. This process is in strong competition with the stepwise N-release expected from different hydrolysis rates determined under abiotic laboratory conditions. This quick microbial transformation and uptake of N from the N-lignin can also explain that addition of N-lignins to soils did not increase their CO2 fixation potential. Thus, at the present stage, our results indicate that further research is needed, before they can be used as efficient slow-release N fertilizer with increasing C-sequestration potential. Additional modifications of their N-binding forms are required which increase their medium term biochemical recalcitrance.
Publications
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Bioavailability and sequestration pattern of N released from recalcitrant humic acid precursors and pyrogenic organic matter: An incubation study. 24th International Meeting of Organic Geochemistry, Bremen, Germany. 6-11 September 2009
De la Rosa, J.M., Liebner, F. Pour, G., Knicker, H.
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How does organic matter affect the N dynamic in agricultural soils? An incubation study. Jahrestagung der Deutsche Bodenkundliche Gesellschaft, 2009, Bonn, 5-13 September 2009
de la Rosa, J.M., Knicker, H.
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How does pyrogenic organic matter affect the N dynamic in agricultural soils? An incubation study. European Geosciences Union General Assembly 2010, Vienna, Austria, 2 – 7 May 2010
De La Rosa, J.M., Knicker, H.
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(2011) Ammonoxidised Lignins as slow nitrogen-releasing soil amendments and CO2-Binding Matrix. Angewandte Chemie – International Edition, 50, A34-A39. A
Liebner, F., Pour, G. de la Rosa Arranz, J.M., Hilscher, A., Rosenau, T., Knicker, H.
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(2011) Bioavailability of N released from N-rich pyrogenic organic matter: An incubation study. Soil Biology and Biochemistry, 43, 2368-2373
De la Rosa, J.-M., Knicker, H.
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(2011) Soil organic N – an underrated player for c-sequestration in soils? Soil Biology and Biochemistry, 43, 1118-1129
Knicker, H.
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Solid-state 13C and 15N NMR spectroscopic analysis of organic matter in a Mediterranean soil after amendment of N- ammoxidized lignins. Eurosoil 2012, Bari, 2-6 July 2012
De la Rosa, J.M., Liebner, F., Pour, P., Knicker, H.
