Landscape-scale variability of N mineralization in forest soils

• Published in: Soil biology & biochemistry 1996-03, Vol.28 (3), p.383-391
• Main Authors: Walley, F.L., Van Kessel, C., Pennock, D.J.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; Microbiology; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(95)00153-0

Our understanding of the controls on N-cycling and availability in forest soils following disturbance is limited. A comparative study was conducted to examine the spatial distribution of soil N in forest soils and assess the effects of site disturbance. Sampling grids were established within a 120 × 120 m representative area at a native site, and at recently (i.e. 4-year-old) burned and clear-cut sites. A three-dimensional classification of landscape form was used to stratify each landscape into distinct landform elements. The spatial distribution of inorganic-N was not related to landform element, irrespective of site disturbance, indicating an absence of topographic control at the scale studied. However, a narrowing of the NH 4 +-to-NO 3 − ratio at the clear-cut site compared to the native site suggests that N-cycling was influenced by site disturbance. Similarly, an increase in the size of the microbial biomass at the clear-cut site, coupled with a widening of the microbial biomass C-to-N ratio, suggest that disturbance altered both the size and composition of the microbial biomass. Potential N and C mineralization, and net nitrification in the forest floor and surface mineral horizons representing two distinct landform complexes were studied in a controlled aerobic 8-wk incubation experiment. Accumulation of NH 4 + and NO 3 − differed markedly between sites although the effects of topographic position were generally non-significant. Inorganic-N accumulated principally as NH 4 + in soils from the native site due to an extended lag in nitrification. In contrast, NH 4 + accumulation in soils from the recently disturbed sites remained limited, whereas NO 3 − accumulation predominated. Thus, although topography did not markedly influence N distribution at the scale studied, site disturbance had a direct effect on N-cycling processes in these forest soils.