One of the main problem of digestate (and other N fertilizer) application is the N leaching. However, Renger & Wessolek (1992) and Knudsen et al. (2006) found that the N leaching was dependent on the use of cover crops. Similar results were reported by Moller & Stinner (2009) who did not find differences in the soil mineral N content among different manuring systems in the case of winter wheat, rye and spelt in autumn, before use of cover crops. That means that the use of cover crops is an appropriate method to avoid N leaching and to compensate for higher N application. From the same experiment, Moller et al. (2008) reported average soil mineral N content in spring. In this case they found significant higher soil mineral N content of the digested slurry treated samples (Table 4).

Digestate contains high proportion of NH4-N therefore it would be expected to increase NH4-N content of treated soil. However, digestate applied in the fall could easily be nitrified by early spring (Rochette et al., 2004; Loria et al., 2007). This predisposed N loss with occurrence of wet conditions.

Generally, the digestate application does not cause any significant changes in the total-N and available P content, while the available K content was increased by the application of biogas residue (Olsen et al., 2008). Similar results have found Vago et al. (2009), who reported the significant increase of 0.01 M dm-3 CaCl2 extractable P content even after 5 L m-2 digestate treatment, while the K content of soil was significantly increased by 10 L m-2 digestate dose only.