2. Materials and methods
2.1. The field experiment and soil sampling
A field experiment with randomized block design was established in autumn 1998 in central Sweden
(59 37 N, 16 33 E). Before the experiment, the soil had not been fertilized with farmyard manure
since 1975. The soil was initially classified as a Eutric Cambisol (FAO 1998) and contained 37–49%
clay, 36–44% silt and 14–20% sand. The experiment was set up with four replicates (blocks) for each
treatment and a plot size of 6×15 m. The crop rotation in the experiment was oats and spring barley every
second year.
The experimental design (Table 1) was chosen to enable comparison of the organic waste with
traditional fertilizer (NPS) and a control with no fertilizer. In order to mimic realistic farm practices, half
of the total nitrogen load (50 kg N ha-1) was applied as mineral fertilizer and the second half as either
sewage sludge or biogas residue (50 kg N ha-1) at a total rate corresponding to 100 kg N ha-1.