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 and assists with maintaining soil quality. However, humification and decomposition processes occurring during feedyard manure's on-farm life cycle influence the forms, concentrations, and availability of carbon (C) and nutrients such as nitrogen (N) and phosphorus (P). Improved understanding of manure organic matter (OM) chemistry will provide better estimates of potential fertilizer value of manure from different feedyard sources (e.g., manure accumulated in pens, stockpiled manure after pen scraping) and in settling basin and retention pond sediments. This will also assist with identifying factors related to nutrient loss and environmental degradation via volatilization of ammonia and nitrous oxide and nitrate leaching. We used Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies to characterize structural and functional properties of OM and water-extractable OM (WEOM) from different sources (surface manure, manure pack, settling basin, retention pond) on a typical commercial beef feedyard in the Texas Panhandle. Results showed that as beef manure completes its on-farm life cycle, concentrations of dissolved organic C and N decrease up to 98 and 95%, respectively. The UV-vis analysis of WEOM indicated large differences in molecular weight, lignin content, and proportion of humified OM between manures from different sources. The FTIR spectra of OM and WEOM indicate preferential decomposition of fats, lipids, and proteins over aromatic polysaccharides such as lignin. Further work is warranted to evaluate how application of feedyard manure from different sources influences soil metabolic functioning and fertility.