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This digital document is a journal article from Soil Biology and Biochemistry, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
The natural ^1^5N abundance (@d^1^5N) of different ecosystem compartments is considered to be an integrator of nitrogen (N) cycle processes. Here we investigate the extent to which patterns of @d^1^5N in grassland plants and soils reflect the effect of different management practices on N cycling processes and N balance. Investigations were conducted in long-term experimental plots of permanent montane meadows with treatments differing in the amount and type of applied fertilizer (0-200kgNha^-^1yr^-^1; mineral fertilizer, cattle slurry, stable manure) and/or the cutting frequency (1-6 cuts per season). The higher @d^1^5N values of organic fertilizers compared to mineral fertilizer were reflected by higher @d^1^5N values in soils and harvested plant material. Furthermore, @d^1^5N of top soils and plant material increased with the amount of applied fertilizer N. N balances were calculated from N input (fertilization, atmospheric N deposition and symbiotic N”2 fixation) and N output in harvest. ‘Excess N’-the fraction of N input not harvested-was assumed to be lost to the environment or accumulated in soil. Taking fertilizer type into account, strong positive correlations between @d^1^5N of top soils and the N input-output balance were found. In plots receiving mineral N fertilizer this indicates that soil processes which discriminate against ^1^5N (e.g. nitrification, denitrification, ammonia volatilization) were stimulated by the increased supply of readily available N, leading to loss of the ^1^5N depleted compounds and subsequent ^1^5N enrichment of the soils. By contrast, in plots with organic fertilization this correlation was partly due to accumulation of ^1^5N-enriched fertilizer N in top soils and partly due to the occurrence of significant N losses. Cutting frequency appeared to have no direct effect on @d^1^5N patterns. This study for the first time shows that the natural abundance of ^1^5N of agricultural systems does not only reflect the type (organic or mineral fertilizer) or amount of annual fertilizer amendment (0-200kgha^-^1yr^-^1) but that plant and soil @d^1^5N is better described by N input-output balances.

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