Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Abstract. Dairy stall bedding material containing gypsum (CaSO₄•2H₂O) has gained popularity, where available, as a recycled material for cow comfort with agronomic benefits once land applied after manure storage. These benefits need to be balanced with potentially dangerous hydrogen sulfide (H₂S) gas release observed during agitation of storages containing gypsum-laden dairy manure. Manure additives have showed promise in reducing H₂S release during both on-farm field demonstrations and bench-scale controlled evaluations of gypsum-laden manure. Potential additives were investigated in the bench-scale trials using experimental vessels containing 15 kg dairy manure each. Two preliminary trials determined that iron oxide (specifically, iron oxide-hydroxide, FeOOH) was effective in mitigating H₂S release. The objective of the investigation presented here was to more thoroughly document H₂S mitigation performance of the most promising formulation, a 1:1 molar ratio of iron oxide to gypsum. Gas release was continuously monitored using a Fourier transfer infrared (FTIR) gas analyzer assembly during an incubation period of 40 days that included three agitation events at days 17, 24 and 31. Results indicated extremely high concentrations of H₂S during most manure agitation events (500 ~ 8000 ppm), while minimum releases were found when samples were static (< 10 ppm). Means of maximum concentrations of H₂S were compared among treatments of each trial. Statistical tests showed that adding iron oxide to gypsum-laden manure significantly (p<0.01) reduced production of H₂S by 83-96% compared to manure without iron oxide. The level of H₂S release was diminished to levels at or below those observed from control manure (without gypsum). Therefore, iron oxide is a promising additive to mitigate H₂S production in gypsum-bedded dairy manure during agitation events.