Using Sterols to Detect Pig Slurry Contribution to Soil Organic Matter

Samples of pig slurry, as well as dairy and poultry manures collected in Brittany (western France) were analysed to test the ability of sterol profiles to provide a fingerprint of pig slurry contribution to soil organic matter. The data show that the 5β-stanol, known as coprostanol, is the most abundant sterol present in pig slurry, whereas this compound occurs only in minor amounts in both poultry and dairy manures. Moreover, systematic variations of (campesterol + sitosterol)/cholesterol (i.e., C₂₈₊₂₉/C₂₇) and (coprostanol + epi-coprostanol)/cholesterol (i.e., 5β/C₂₇) ratios allow to discriminate clearly pig slurry from poultry and dairy manures. The robustness of the pig slurry “sterol fingerprint” was tested by analysing the sterol profiles of soil samples from an experimental field that had received a massive pig slurry input between 10 to 14 years ago. The results indicate that the specific sterol profile of pig slurry is conservative once the slurry has been incorporated into the soil. In particular, the diagnostic 5β/C₂₇ ratio proves to be constant with time in soils having received pig slurry application, even 10 years after the end of the application. The “sterol fingerprint” of pig slurry is thus sufficiently distinctive from dairy and poultry manures, and also sufficiently time-resistant, to be of diagnostic value in determining whether a soil sample was once contaminated by pig slurry.