Injection of pig slurry and its effects on dynamics of nitrogen and carbon in a loamy soil unter laboratory conditions

Dynamics of nitrogen (N) and carbon (C) were investigated in a loamy soil amended or injected with pig slurry. Treatments were with or without acetylene C₂H₂ (which is assumed to inhibit reduction of nitrous oxide (N₂O) to dinitrogen (N₂), and soil cores were conditioned for 15 days at 25°C while pH, production of CO₂ and N₂O, ammonia (NH₃) emission and (nitrate) (NO₃ ^–) and (ammonium) (NH₄ ⁺) concentrations were monitored. There was no significant difference in CO₂ production between the injected and surface applied pig slurry treatments, and within 15 days ca. 5% of the C applied had been mineralized, if no priming effect was assumed. Neither the production of N₂O nor the total gaseous production of the denitrification process (N₂O plus N₂) were affected by the way the pig slurry was added to the soil. NH₃ volatilization, however, decreased by 90% when pig slurry was injected. The addition of C₂H₂ significantly increased the CO₂ production and the concentration of NH₄ ⁺, but significantly decreased the concentration of NO₃ ^–. It was concluded that the injection of pig slurry to a dry soil was an acceptable alternative to its application to the soil surface, as not only was NH₃ volatilization reduced, but the production of N₂O and N₂ through denitrification was not stimulated. It is also suggested that the composition of the organic C fraction in the pig slurry, most likely the concentration of fatty acids, had an important effect on the dynamics of N and C in the soil. Received: 12 May 1997