Effects of liming and mineral N on initial decomposition of soil organic matter and post harvest root residues of poplar

- Liming decreases C mineralization of humified organic matter and plant residues.
- Addition of mineral N to root amended soil increased CO2 derived from organic matter.
- But this N effect was canceled out if lime and N were applied simultaneously.
- A decreased decomposition of roots after liming is observed, by higher amounts of POM.
- No effect on POM was observed after concomitant addition of mineral nitrogen and lime.

Short-term potential carbon (C) and nitrogen (N) mineralization of soil organic matter and belowground plant litter was determined in the top soil layer of a sandy soil of a short-rotation coppice (SRC) and the effect of addition of lime, mineral nitrogen and poplar roots was determined. Lime addition was equivalent to 1.2 mg CaCO3 g− 1, mineral N and root litter were added corresponding to 6.8 μg N g− 1 and 13.8 mg roots g− 1 soil respectively. Partitioning of carbon dioxide (CO2) derived from lime and soil organic matter (SOM) was calculated by using stable isotope analysis of the CO2. In addition, particulate organic matter (POM) as well as microbial biomass carbon and nitrogen were analyzed after 51 days of incubation.Addition of lime decreased CO2 derived from organic matter in all treatments, but the level of decrease varied with N and root litter addition. Microbial biomass C and N increased with N addition in soil without root litter but decreased with root litter, nevertheless an immobilization of mineral N was especially high in soil amended with root litter. Particulate organic matter (POM) decreased by 41% of its dry weight in root litter amended soil. Liming decreased decomposition of POM in these soils, whereas no effect was observed after addition of mineral nitrogen or mineral nitrogen and lime. These results show that liming has the potential to decrease C mineralization of humified organic matter as well as plant residues and that decreased mineralization of organic matter occurred after liming, even if mineral N was added.