Two organic fertilizers were prepared from the same initial mixture of poplar sawdust, blood and flour either by composting in a reactor or by chemical oxidation. Both processes resulted in loss of c. 30% of the organic matter. Composting required 90 days in comparison to only a few hours with chemical oxidation. Extraction of the organic residues with 1 N KOH gave solutions containing 24·6 and 15·1 g/l of humic substances respectively. These humic solutions were applied to pot-grown Lolium multiflorum Lam. at 4 and 10 mg carbon per pot to assess the short-term uptake of macro and microelements by the plants. When the plants were short of phosphorus, the humic substances from the chemically decomposed sawdust supplied at 10 mg C per pot improved total P uptake and yield. Humic substances also increased copper and manganese uptake, and by enhancing root development, also improved nitrogen uptake and biomass yield.