Bioavailability of N released from N-rich pyrogenic organic matter: An incubation study

In Mediterranean ecosystems, natural wildfires and prescribed burning play an important role. In order to obtain a better understanding of the impact of charcoal on the nitrogen (N) cycling in soil, N-15-enriched pyrogenic organic material (PyOM) obtained from Lolium perenne charred for 4 min at 350 degrees C was mixed with a typical Mediterranean agricultural soil and incubated for 72 days under controlled conditions. The main objectives were to analyze the availability of N from this material and to obtain more insight into the recalcitrance of PyOM in soils. Addition of artificially produced N-15-PyOM increased the biomass production and N retention. After 72 days of incubation time, 10% of the N-15 added to the soil (N-15(add)) was incorporated into new grass biomass. Solid-state N-15 NMR spectroscopy revealed that at least some of this N derived from the degradation of pyrrole-type structures. Increase of the amide-N intensity in the solid-state N-15 NMR spectrum of the incubated soils indicated further that some N-15 from the PyOM was also incorporated into new microbial biomass. Our results confirmed a relatively low recalcitrance of N-rich PyOM. Since during its degradation, N is only slowly transferred into a plant-available form, it may contribute to the observed improvement of soil fertility by avoiding fast N losses due to leaching and volatilization as a slow N-release fertilizer. (C) 2011 Elsevier Ltd. All rights reserved.