Effects of humic substances from composted or chemically decomposed poplarsawdust on mineral nutrition of ryegrass

Two organic fertilizers were prepared from the same initial mixture of popl ar sawdust, blood and flour either by composting in a reactor or by chemica l oxidation. Both processes resulted in loss of c. 30 % of the organic matt er. Composting required 90 days in comparison to only a few hours with chem ical oxidation. Extraction of the organic residues with 1 N KOH gave soluti ons containing 24.6 and 15.1g/l of humic substances respectively. These hum ic solutions were applied to pot-grown Lolium multiflorulm Lam. at 4 and 10 mg carbon per pot to assess the short-term uptake of macro and microelemen ts by the plants. When the plants were short of phosphorus, the humic subst ances from the chemically decomposed sawdust supplied at 10 mg C per pot im proved total P uptake and yield. Humic substances also increased copper and manganese uptake, and by enhancing root development, also improved nitroge n uptake and biomass yield.