B094-0001
A Decade of Nitrogen Fertilization Alters Soil Organic Matter Composition and Degradation in A Temperate Agroecosystem

Tuesday, 15 December 2020
Poster
Meiling Man1, Bill Deen2, Kari Edith Dunfield3, Claudia Wagner-Riddle3 and Myrna J Simpson4, (1)University of Toronto Scarborough, Department of Physical and Environmental Sciences, Toronto, ON, Canada, (2)University of Guelph, Department of Plant Agriculture, Guelph, ON, Canada, (3)University of Guelph, School of Environmental Sciences, Guelph, ON, Canada, (4)University of Toronto, Toronto, ON, Canada
Abstract:
Nitrogen (N) fertilization in agroecosystems has been reported to alter soil carbon storage, however, little information is available on soil organic matter (OM) compositional changes. Soil samples (0-10 cm) were collected from a 10-year experiment with increasing rates of N fertilization (control, 30, 87, 145 and 260 kg ha-1 yr-1) at the Elora Research Station, Ontario, Canada. The soil samples were analyzed for organic carbon, total N contents, molecular-level OM composition and microbial biomass and community structure. Despite similar organic carbon and total N contents for the samples across all treatments, we observed generally lower plant-derived compounds including steroids, cutin- and suberin-derived compounds under some N addition treatments. This is consistent with lower alkyl carbon contents from solid-state 13C nuclear magnetic resonance (NMR) spectroscopy analysis. The decreased plant-derived compounds (i.e. steroids and cutin-derived compounds) may be attributed to higher degradation of these compounds likely associated with elevated microbial biomass under N fertilization. Lignin-derived phenols increased under N addition, which is consistent with higher aromatic/phenolic carbon contents (mainly derived from lignin) from NMR analysis. The enhanced lignin degradation, which is in line with elevated fungal biomass (lignin degraders), did not result in lower lignin-derived compound or aromatic/phenolic carbon content under N addition. As other studies reported higher lignin contents in corn residues under N fertilization, we suggest that the turnover of lignin-derived phenols may be controlled by not only biodegradation but also the quantity and quality of crop residues. Furthermore, we observed that different N rates exert various controls on soil OM cycling. For example, the increase in degradation of steroids, cutin and lignin was smaller above the threshold N rates 145 kg ha-1 yr-1, implying that the degradation of these compounds was fertilization rate-dependent. Our study highlights that different N fertilization levels alter soil OM dynamics likely through changing a combination of microbial degradation and the quantity and quality of crop residues.
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