Nitrous oxide from beef cattle manure: Effects of temperature, water addition and manure properties on denitrification and nitrification†

Abstract

Beef feedyards produce nitrous oxide (N2 O), a potent greenhouse gas. Limited research has evaluated the processes that produce feedyard N2 O, and how rainfall and temperature impact N2 O losses. Manure in feedyard pens develops into a complex ecosystem of microbes, extracellular enzymes, feces, and urine, with varying H2 O content. This study aimed to improve understanding of feedyard N cycling under differing environmental conditions by incubation of manure in simulated feedyard pens using large chambers under laboratory conditions. We hypothesized that nitrification was the primary source of feedyard N2 O, with interactions among temperature, H2 O content, and manure properties. Emissions of N2 O were monitored with a real–time N2 O analyzer. Manure samples were taken at intervals for analyses of physicochemical properties, denitrification enzyme activity (DEA), and nitrification activity (NA). Due to equipment limitations, there was only one chamber per temperature tested. Correlation was poor among N2 O emissions and rates of DEA and NA. However, significant relationships were found among key manure characteristics, such as ammonia/ammonium and nitrate/nitrite concentrations, manure dry matter, redox status, and temperature. These data suggest that most N2 O was derived from denitrification in the top 5 cm of the manure pack. Further study is warranted to identify the processes involved in flushes of N2 O emitted immediately after rainfall, possibly due to abiotic chemical reactions that release N2 O sequestered in manure pores.