Potential for Nitrate and Fe(III) Additions to Control Indicator Bacteria, Retain Nitrogen, and Reduce Odors in Beef Cattle Feedlot Soils.

A wide variety of volatile odor compounds accumulate during the anaerobic fermentation of livestock wastes.  Since these compounds are easily degraded in other environments when alternate electron acceptors (compounds other than O₂) are available, we evaluated the use of amending NO3- and Fe(III) into mixtures of cattle feedlot manure as a way to minimize the production and persistence of odor compounds.  Pan incubations were conducted with dry feedlot waste amended with Fe(III), NO₃^-, or no electron acceptor (fermentative control).  Over several days, odor compounds and electron acceptors were monitored before and after a simulated rainfall event.  Addition of alternate electron acceptors affected many of the measured soil parameters including pH, ammonia content, fecal coliforms, H₂ gas production, total VFA, and branched-chain VFA.  Compared to the standard fermentative control, iron treatments exhibited a three to four-fold increase in malodorous VFA content (6 to 8 mg VFA/g dry soil), increased fecal coliform content (10-fold higher), and decreased pH (2 unit decrease), which would greatly enhance VFA emission.  However, one positive for the iron treatment was its greater ammonia content (>3 mg N/g dry soil) compared to controls which retained no ammonia.  The nitrate treatment was superior to controls (and iron treatments) based upon its 100-fold lower fecal coliform content, high final pH (9.9), and its low content of branched-chain VFA.  We conclude that nitrate amendment was the most effective for short-term control of many manure issues, while application of iron amendment may not prove to be a viable odor solution without further research because of the excessive accumulation of branched-chain VFA and coliform bacteria.