EFFECT OF CARBON CONSTITUENTS IN MANURE ON DENITRIFICATION IN SOIL

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Abstract
Nine different manures were evaluated to determine their ability to supply carbon to denitrifying bacteria in waterlogged soil. Manure slurries (anaerobically decomposed) and stacked or composted manures (aerobically decomposed) were included in this study. Water-soluble C concentration was considerably higher in the slurries than in the stacked or composted manures. Volatile fatty acids (VFA, including acetate, propionate, and butyrate) were significant components of water-soluble C in the slurries. Concentrations of VFA ranged from 5.9 to 26.1 g kg−1 in the slurries. Nitrous oxide production (denitrification) and CO2 evolution in manure-amended soil was closely related to both water-soluble C and VFA concentrations in the manures. In a second experiment, acetate, propionate, and butyrate appeared to be equally effective C sources for denitrifiers in soil amended with dairy cattle slurry. Nitrous oxide production was better correlated with VFA disappearance than with water-soluble C disappearance. Volatile fatty acids were produced during decomposition of solid poultry manure in soil under anaerobic conditions. These VFA were produced from readily available C substrates by fermentative bacteria and accumulated after NO3− had disappeared through denitrification. Denitrification in manure-amended soil depends on the source of manure and the kind and extent of decomposition that occurred in the manure. Key words: Slurry, water soluble carbon, volatile fatty acids