Gross mineralization from plant residues using cross-labelling

Three greenhouse experiments were carried out to measure gross mineralization rate (GMR), inorganic N dynamics, and plant-N uptake from soybean residues and fertilizer N/residue interactions. The soil was a sandy loam from the Krumbach region of Austria. Gross mineralization was measured using 15N-dilution and cross-labelling techniques. Soil was mixed with 15N-labelled or unlabelled soybean residues and packed into PVC columns, which were injected with 20 mg N kg-1 soil, in the form of either labelled (10 atom % 15N excess.) or unlabelled NH4NO3, 11, 15 and 22 days after residue incorporation. Columns were sampled 2 and 4 days after injection, and analysed for water content, inorganic N, and the 15N-enrichment of inorganic-N pools