Response of Soil Inorganic Nitrogen to Land Use and Topographic Position in the Cofre de Perote Volcano (Mexico)

摘要

This study addressed the effects of land use and slope position on soil inorganic nitrogen and was conducted in small watersheds. The study covered three land use types: tropical cloud forest, grassland, and coffee crop. To conduct this research, typical slope small watersheds were chosen in each land use type. Slopes were divided into three positions: shoulder, backslope, and footslope. At the center of each slope position, soil sampling was carried out. Soil inorganic nitrogen was measured monthly during a period of 14 months (July 2005-August 2006) with 11 observations. Significant differences in soil NH_4~+-N and NO_3~--N content were detected for both land use and sampling date effects, as well as for interactions. A significant slope position-by-sampling date interaction was found only in coffee crop for NO_3~--N content. In tropical cloud forest and grassland, high soil NH_4~+-N and low NO_3~--N content were recorded, while soil NO_3~--N content was high in coffee crop. Low NO_3~--N contents could mean a substantial microbial assimilation of NO_3~--N, constituting an important mechanism for nitrogen retention. Across the entire land use set, the relationship between soil temperature and soil inorganic N concentration was described by an exponential decay function (N = 33 + 2459exp~(-0.23T), R~2 = 0.44, P < 0.0001). This study also showed that together, soil temperature and gravimetric soil water content explained more variation in soil inorganic N concentration than gravimetric soil water content alone.