Nitrogen storage and C:N ratio of an Umbrisol under forest management in Durango, Mexico

Abstract

Forest activities exert a positive or negative influence on soil ecosystem properties and services, through changes in vegetation and microclimate. The removal of biomass alters the carbon (C) and nitrogen (N) cycles, which are important indicators of soil health. The objective of this study was to determine the reservoir of N and the C:N ratio at two different depths of an Umbrisol, considering three stands with forest management (Clearcutting, Parent Trees and Selection) and a post-fire regenerated area, all of them eight years after the intervention, and a control plot as reference stand in a Pinus-Quercus forest. Results indicate significant differences in the variables for both soil depths (Total N, organic C, C:N ratio, N reservoir Mg ha^-1). The observed contents of total nitrogen (>0.10 %) are considered very high, being ascribable to the nature of the Umbrisol and to the quality of the organic matter of this ecosystem, with the ensuing impact on the C:N ratio, which is slightly above the optimal ranges of mineralization, having an average value of 20.4 at both depths. On the other hand, the nitrogen reserve for the analyzed profile ranged between 5.03 (control) and 9.63 Mg ha^-1 (Parent Trees). Particularly, the Clearcutting and Parent Trees treatments showed differences in regard to the Control, such treatments accelerated the incorporation of organic material to the soil (roots, branches, leaves), causing increases from 79 to 91 % in the nitrogen reservoir.