Incorporation of nitrogen from crop residues into light-fraction organic matter in soils with contrasting management histories |
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Authors: | Gary D Bending Mary K Turner |
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Institution: | (1) Warwick HRI, University of Warwick, Wellesbourne, Warwickshire, CV35 9EF, UK |
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Abstract: | The proportion of N from crop residues entering the light-fraction organic matter (LFOM) pool was investigated in soils with
contrasting soil organic matter and microbial characteristics arising from different management histories. A laboratory experiment
was conducted in which 15N-labelled sugar beet, Brussels sprout or ryegrass shoots, which possessed a range of C/N contents, and hence different biochemical
qualities, were incorporated into a sandy–loam soil collected from within a field (FC) or from the field margin (FM). Amounts
of C and N incorporated into LFOM were determined after 112 days. The FC and FM soils had organic C contents of 0.9% and 2.5%,
respectively. Addition of crop residues increased total LFOM N content and reduced its C/N in FC soil but had no effect on
total LFOM N or its C/N in FM soil. Ryegrass incorporation into FC was the only treatment in which there was a net increase
in LFOM C. Isotopic analysis indicated that more crop-residue-derived N became incorporated into the LFOM N pool in FM relative
to FC soil, with per cent crop residue N incorporated ranging from 25.9% to 35.3% in FC and between 38.9 and 68.5 in FM. Incorporation
of crop residues had a positive priming effect on pre-existing LFOM N in FM but not FC soil. We conclude that the characteristics
of plant material, together with differences in soil organic matter and microbiology resulting from contrasting management,
determined the amount of crop residue C and N incorporated into both HFOM and LFOM. |
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Keywords: | Soil organic matter Light-fraction organic matter Crop residue quality Decomposition Priming |
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