Analysis of livestock slurries from farms across Northern Italy: Relationship between indicators and nutrient content

Livestock waste composition varies significantly because of differing management practices; diet, cleaning system, bed system, etc. Unfortunately, measurements of the waste nutrient content are not frequently carried out on farms since laboratory analyses take time and are generally impractical for many farmers. As a result when slurry is distributed on the land its precise fertiliser value is often unknown. In this study 132 slurry samples were collected from pig and cattle farms in the Lombardy region of Italy. Three pig- and two cattle-farming systems were studied individually and jointly. Samples were analysed in a laboratory for electrical conductivity (EC), pH, dry matter content (DM), total Kjeldahl nitrogen (TKN), total ammonium nitrogen (TAN), phosphorus (as P2O5) and potassium (as K2O). The possibility of estimating the slurry nutrient content on the basis of more readily measured parameters (i.e. pH, EC) was evaluated. Correlations between fertiliser values (NPK), physical–chemical properties and variation in slurry composition were therefore studied. Significant differences in slurry composition were found between the different farming systems. Although no significant correlation was found between pH and NPK compounds, EC and DM proved useful to predict fertiliser elements. In particular, EC was found to be the best estimator for nitrogen compounds and potassium.