Operator Exposure to Hydrogen Sulfide from Dairy Manure Storages Containing Gypsum Bedding.

Dairy manure storages containing gypsum-based bedding have been linked anecdotally with injury and death due to presumed dangerous levels of gases released. Recycled gypsum products are used as a cost-effective bedding alternative to improve animal welfare and provide agronomic benefits to manure recycled back to the land. Sulfur contained in gypsum (calcium sulfate) can contribute to hydrogen sulfide (H2S) gas formation under the anaerobic storage conditions typical of dairy manure slurry. Disturbance of stored manure during agitation releases a burst of volatile gases. On-farm monitoring was conducted to document conditions during manure storage agitation relative to gas concentration and operator safety. One objective was to document operator exposure to H2S levels; therefore, each operator wore a personal gas monitor while performing tasks associated with manure storage agitation. Data from three dairy bedding management categories on ten farms were compared: (1) traditional organic bedding, (2) gypsum bedding, and (3) gypsum bedding plus a manure additive thought to reduce H2S formation and/or release. Portable meters placed around the perimeter of dairy manure storages recorded H2S concentrations prior to and during 19 agitation events. Results show that farms using gypsum bedding produced higher H2S concentrations during manure storage agitation than farms using traditional bedding. In most cases, gypsum-containing manure storages produced H2S levels above recognized safe thresholds for both livestock and humans. Farm operators were most at risk during activities in close proximity to the manure storage during agitation, and conditions 10 m away from the storage were above the 20 ppm H2S threshold on some farms using gypsum bedding. Although H2S concentrations rose to dangerous levels, only two of 18 operators were exposed to >50 ppm H2S during the first 60 min of manure storage agitation. Operators who are aware of the risk of high H2S concentrations near gypsum-laden manure storages can reduce their exposure risk by working upwind and away from the H2S plume within a closed tractor cab.

Effects of Feeding Encapsulated Nitrate to Beef Cattle on Ammonia and Greenhouse Gas Emissions from Their Manure in a Short-Term Manure Storage System.

A study was conducted to investigate effects of feeding encapsulated nitrate (EN) to beef cattle on ammonia (NH) and greenhouse gas emissions from their manure. Eight beef heifers were randomly assigned to diets containing 0 (control), 1, 2, or 3% EN (55% forage dry matter; EN replaced encapsulated urea in the control diet and therefore all diets were iso-nitrogenous) in a replicated 4 × 4 Latin square design. Urine and feces collected from individual animals were reconstituted into manure and incubated over 156 h using a steady-state flux chamber system to monitor NH, methane (CH), carbon dioxide (CO), and nitrous oxide (NO) emissions. Urinary, fecal, and manure nitrate (NO)-N concentration linearly increased ( < 0.001) with feeding EN, and urinary urea concentration tended to be lower ( = 0.078) for EN versus Control. The hourly emissions of NH, CO, and NO (mg head h) were not affected, although NH emission rates tended to be lower ( = 0.070) for EN compared with Control at 0 to 12 h. Cumulative NH, CO, and NO emissions over 156 h were not affected, but CH emissions were less (4.5 vs. 7.4 g head; = 0.027) for EN compared with Control. In conclusion, although NH emissions were initially lower for EN manures, total NH emitted over 156 h was not affected. Dietary EN lowered CH emissions from manure, and, despite greater NO concentrations in EN manure, NO emissions were not affected in this short-term incubation.