Title: Characterization of organic matter in beef feedyard manure by Ultraviolet-Visible and Fourier transform infrared spectroscopies Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 2013
Publication Date: March 1, 2014
Citation: Waldrip, H., He, Z., Todd, R.W., Hunt, J.F., Rhoades, M.B., Cole, N.A. 2014. Characterization of organic matter in beef feedyard manure by Ultraviolet-Visible and Fourier transform infrared spectroscopies. Journal of Environmental Quality. 43:690-700. Interpretive Summary: Manure from beef cattle in feedlots is an important nutrient source for plants. Feedlot manure also helps to maintain soil quality. The organic matter in beef manure breaks down as it ages in the feedlot, which can change manure carbon, nitrogen, and phosphorus characteristics. A better understanding of the chemistry of the organic matter in feedlot manure could help improve our idea of how manure taken from different sources on a feedlot will influence soil quality. It could also help identify things that lead to feedlot nitrate and ammonia losses. We used Fourier-transform infrared and UV-visible spectroscopies to look at the structure of whole organic matter and water extractable organic matter in feedlot manure from different sources (surface manure, manure pack, settling basin, retention pond) at a commercial beef feedlot in Texas. We also looked at changes in organic matter from feedlot manure after it was applied to soil. We found that the amount of dissolved organic carbon was reduced by as much as 98% as manure ages and moves through the feedlot. We also found that dissolved nitrogen was up 95% lower in older feedlot manure. UV-vis analysis of dissolved organic matter showed big differences in molecular weight, and the amount the amount of lignin and humified organic matter in feedyard manures from different sources. The FT-IR spectra of whole and dissolved organic matter were like humic acids found in soil and other kinds of manure. A comparison of of manures taken from different feedlot sources showed that fats, lipids and proteins were broken down faster than lignin and other complex carbohydrates. We need to do more work to see how applying manure from different feedlot sources will influence soil quality and fertility.
Technical Abstract: The manure from beef cattle feedyards is a valuable source of nutrients for crops and assists with maintaining soil 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 fertilizer value. 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 help identify factors that could 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 comparatively 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) from a typical commercial beef feedyard in the Texas Panhandle. In addition, we also evaluated the changes in OM and WEOM from feedyard 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 (DOC) and N are decreased by up to 98 and 95%, respectively. 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 were typical of humic acids and comparison of spectra from manures taken from different feedyard locations showed preferential decomposition of fats, lipids and proteins over aromatic polysaccharides, such as lignin. Further work is warranted to evaluate how application of different feedyard manures influences soil metabolic functioning and fertility.