Competition for nitrogen during mineralization of plant residues in soil: Microbial response to C and N availability

In an experiment where N-poor (barley straw) and N-rich (clover leaves) plant residues were placed into soil as separate layers, negative effect of plant roots on microbial growth was observed. The depression effect occurred predominantly in N-poor plant residue layers, which indicated that microbial growth can be limited by N availability in such microsites in soil. More energy substrates were available in the planted straw layer, as indicated by a significantly higher N immobilization potential in the planted soil compared with that in the unplanted soil. However, in the N-rich sites, plant roots stimulated N mineralization during 1 wk incubation of soil slurries. Microbial response to initial growth conditions, including C and N availability, are also discussed. (C) 1997 Elsevier Science Ltd.