Characterization of Organic Matter in Beef Feedyard Manure By Ultraviolet-Visible and Fourier Transform Infrared Spectroscopies.

Manure from beef cattle feedyards is a valuable source of nutrients for crops and assists with maintaining soil fertility and quality. However, the humification and decomposition processes that occur during feedyard manure’s on-farm life cycle will influence the forms, concentrations, and availability of carbon (C) and nutrients such as nitrogen (N) and phosphorus (P), thereby affecting its value as fertilizer and organic amendment. An improved understanding of the chemistry of feedyard manure organic matter (OM) will provide better estimates of the potential fertilizer value of manure taken from different sources on a feedyard and may help identify factors, such as the presence of amines and other N-containing functional groups, that lead to nutrient loss via ammonia and nitrous oxide volatilization and nitrate leaching. In this study, we utilized Fourier-transform infrared (FT-IR) and UV-visible (UV-vis) spectroscopies to characterize the structural and functional properties of OM in feedyard manure and water extractable OM (WEOM) taken from different locations (surface manure, manure pack, settling basin, retention pond) at a typical commercial beef feedyard in the Texas Panhandle. In addition, we used FT-IR and UV-vis spectroscopies to evaluate the changes in OM and WEOM of pen manure following surface application to rangeland. The primary findings were that, as beef manure completes its on-farm life cycle, concentrations of dissolved organic C and N can be decreased by as much as 98%. UV-vis spectral analysis of WEOM indicated large differences in molecular weight, lignin content, and proportion of humified OM between the manures from different sources. The FT-IR spectra of whole manures and WEOM from different sources were typical of humic acids, and indicate preferential decomposition of fats, lipids, and proteins over aromatic polysaccharides. Further work is required to evaluate how the application of different feedyard manures will influence soil metabolic functioning and fertility.