Nitrogen Recovery of a Digested Dairy Cow Slurry, its Liquid and Solid Fractions, and of a Dairy Cow Slurry Daniele Cavalli 1 , Giovanni Cabassi 2 , Silvia Motta 2 , Lamberto Borrelli 2 , Luigi Degano 2 , Luca Bechini 1 , Pietro Marino 1 1 Department of Agricultural and Environmental Sciences – Production, Landscape, Agroenergy, Università degli Studi di Milano, IT, daniele.cavalli@unimi.it 2 Consiglio per la Ricerca e la sperimentazione in Agricoltura (CRA) – Fodder and Dairy Productions Research Centre (CRA-FLC), IT Introduction Knowing the crop recovery of N applied with livestock slurries is essential to formulate a nutrient management plan that reduces economic costs and unwanted N emissions to the environment. Among livestock slurries, digested slurries are still relatively less studied. They are normally rich in ammonium and have a recalcitrant organic fraction. After soil application, part of the ammonium contained in digested and undigested livestock slurries can be immobilised in soil microbial biomass, and subsequently remineralised. The organic N is slowly mineralised during several seasons. Incubation experiments (e.g. Bechini and Marino, 2009) suggest that in the short term most of the fertilising value of these slurries is due to their ammonium content. In the subsequent years, it is then necessary to take into account the residual effect, due to the slow mineralisation of the organic fraction and the remineralisation of previously immobilised mineral nitrogen. In the two-year experiment described here, we wanted to verify this hypothesis in the field, comparing ammonium sulphate, a digested slurry, its solid and liquid fraction, and a raw cow slurry. Material and Methods Field experiment The field used for the experiment is located at the experimental station of Consiglio per la Ricerca e la sperimentazione in Agricoltura – Research Unit for Vegetable Crops (CRA-ORL) in Montanaso Lombardo (Lodi), Italy (45°20’ N, 9°26’E). The field was cultivated with barley (Hordeum vulgare L.) and maize (Zea mays L.) until the beginning of the experiment and did not receive organic fertilisers in the previous ten years. The characteristics of the 0-30 cm soil layer are: sand 47%, silt 39%, clay 14%, pH(H 2 O) 5.8, total N and organic C (% DM) 0.13 and 0.93. A total of six treatments were established corresponding to the application of five fertilisers and a control treatment: 1) control without N fertilisation (CO); 2) ammonium sulphate (AS); 3) digested dairy cow slurry (DS); 4-5) the liquid (LF) and solid (SF) fractions after mechanical separation of DS; and 6) undigested dairy cow slurry (SL). Table 1. Characteristics of the fertilisers used in the field experiment. Treatment Year DM (%) C (% DM) Total N (% DM) NH 4 -N (% DM) C/Org. N (g C g N -1 ) pH (H 2 O) DS 2011 6,5 39,6 5,6 2,5 13,0 8,0 2012 6,1 38,9 6,1 2,9 11,9 8,2 LF 2011 4,8 36,4 6,7 3,4 11,1 8,0 2012 5,4 38,4 6,5 3,3 11,9 7,9 SF 2011 25,7 44,0 2,2 0,5 26,2 9,6 2012 29,6 43,7 2,1 0,8 33,3 9,0 SL 2011 8,2 43,6 3,9 2,1 23,7 7,3 2012 8,4 42,8 4,3 2,2 20,0 7,3 Sessione Sistemi Colturali 001