Transformation of organic matter and the emissions of methane and ammonia during storage of liquid manure as affected by acidification

Abstract

Acidification of livestock manure can reduce emission of the greenhouse gases methane (CH4) and nitrous oxide (N2O), as well as ammonia (NH3). We examined the relation between emission of these gases and transformation of organic matter as affected by acidification. Liquid cattle manure was acidified with sulfuric acid to pH 5.5 at a pilot scale (100 L), and we measured effects on CH4, N2O, CO2 and NH3 emissions and on transformation of pH buffer components and organic matter. Acidification reduced NH3 emissions by 62% (47 d) and emission of CH4 by 68% (57 d). Emissions of N2O were negligible, probably due to the absence of a surface crust. Reductions in NH3 and CH4 emission were highest at the start but declined over time concomitantly with a gradual increase in the stored liquid manure pH. Acidification did not significantly affect CO2 emissions. Emission of CO2 was high, fiveto ten-fold of CH4 emissions, until Day 16 of storage, after which the CO2 emission rate declined to around twice the CH4 emission rate; consequently, the majority of C loss during the early stages of storage was CO2. Cumulative emission of C in CO2 and CH4 closely matched depletion of dissolved organic carbon (DOC), suggesting that DOC may be a predictor for CH4 emission from dilute slurries. volatile fatty acid and total ammoniacal nitrogen concentrations in surface layers were substantially higher than at the center of stored liquid manure, perhaps resulting from microbial activity at the surface. This pattern deserves attention when predicting NH3 emission from stored slurry.