Nitrogen immobilization and mineralization during initial decomposition of15N-labelled pea and barley residues |
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Authors: | E. S. Jensen |
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Affiliation: | (1) Plant Nutrition, Environmental Science and Technology Department, Risø National Laboratory, DK-4000 Roskilde, Denmark |
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Abstract: | The immobilization and mineralization of N following plant residue incorporation were studied in a sandy loam soil using15N-labelled field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) straw. Both crop residues caused a net immobilization of soil-derived inorganic N during the complete incubation period of 84 days. The maximum rate of N immobilization was found to 12 and 18 mg soil-derived N g–1 added C after incorporation of pea and barley residues, respectively. After 7 days of incubation, 21% of the pea and 17% of the barley residue N were assimilated by the soil microbial biomass. A comparison of the15N enrichments of the soil organic N and the newly formed biomass N pools indicated that either residue N may have been assimilated directly by the microbial biomass without entering the soil inorganic N pool or the biomass had a higher preference for mineralized ammonium than for soil-derived nitrate already present in the soil. In the barley residue treatment, the microbial biomass N was apparently stabilized to a higher degree than the biomass N in the pea residue treatment, which declined during the incubation period. This was probably due to N-deficiency delaying the decomposition of the barley residue. The net mineralization of residue-derived N was 2% in the barley and 22% in the pea residue treatment after 84 days of incubation. The results demonstrated that even if crop residues have a relative low C/N ratio (15), transient immobilization of soil N in the microbial biomass may contribute to improved conservation of soil N sources. |
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Keywords: | Immobilization Mineralization 15N-labelled crop residues Residue quality Soil microbial biomass |
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