Växtnäringseffekter av rötrest i fältförsök med vårsäd

Large amounts of plant nutrients are transported from rural to urban areas in the form of food. To reach circulation of these nutrients, a transport of plant nutrients back to the countryside is necessary. Food residues may be processed in biogas plants where anaerobic processes take place and biogas is produced. The effluents from biogas production can be used as fertilizers in agriculture. The aim of this study was to investigate the effects of effluents from digestion of food residues as a fertiliser to cereals. The study has been based on results from a field trial with oats run by JTI at a farm just north of Uppsala. The field trial was arranged with randomised blocks with four replicates. Effluents from digestion of food residues from the biogas plant of SKAFAB/SRV in Sofielund, Stockholm, were applied at two different times. The first application of effluents was in spring just before sowing and the second application during growth, when the crop was 20 cm high. For comparison of nitrogen efficiency mineral fertilisers were also applied in separate treatments. The total amount of nitrogen in the crop was analysed at two occasions, starting when the oat plants had one node and at time for harvest. On these occasions soil samples were also analysed for ammonium and nitrate nitrogen. The weather had a large impact on the development and yield of crops during the growing season. The persistent rainfall resulted in a large mineralisation of organic nitrogen in the soil. A large uptake of nitrogen and a lush crop growth resulted in lodging for most of the treatments. The untreated plots yielded most grain and lodging was less severe than in treated plots. The differences in yield were small in plots fertilised with effluents from digestion at sowing time and those fertilised during growth. Treatments with effluents from digestion and mineral fertilisers produced equal yield when they were based on the same amount of ammonium nitrogen. No significant differences in the analysis of nitrogen content were found in the different treatments, but there were differences in protein content between them. Grains from the untreated control part had a lower protein content than grains in the fertilised parts. During the end of the growing season, there were large amounts of nitrogen left in the soil, mainly in the fertilised parts. Since weather conditions largely influence yields of crops, there is a need for a long period of field trials with effluents from digestion of food residues to eliminate the influence of weather conditions.