Riaz,M., Mian,I.A. and Cresser,M.S.(2009): Controls on inorganic N species transformations and potential leaching in freely drained sub-soils of heavily N-impacted acid grassland. Biogeochemistry, 92, 263-279.

『非常に強く窒素の影響を受けた酸性草地の自由に流出する地下土壌における無機窒素化学種の変態および潜在的な浸出に対するコントロール』

『Abstract
　In N-polluted, minimally managed soils, recent research has shown that ammonium-N, as well as nitrate-N, may move down through soil profiles. There is a need, therefore, to reassess what controls N species transformations below the rooting depth in such soils. The changes with depth down to 1 m in extractable ammonium-N and nitrate-N concentrations have been studied for two heavily N-impacted acid grassland soils bear York, UK, for fresh soils and for soils incubated after either deionised water (d.w.) or ammonium-N spiking. although in close proximity, the profiles showed marked differences in their relationships of ammonium- and nitrate-N to soil pH, C％, N％ and C:N ratio. One profile was slightly more acidic at the surface, which seems to have changed the distribution of organic matter throughout the soil profile. Trends in ammonium production with depth were clearer when ammonium-N concentrations were recalculated on the basis of ammonium-N per unit mass of soil organic C. This then allowed a consistent trend with soil pH to be discerned for both profiles. Ammonium-N spiking showed that ammonium substrate availability was limiting potential net nitrification rate at 20-60 cm depth for both profiles. Potential mineral-N production was considerable at depth, which would facilitate transport of N to surface waters and/or groundwaters.

Keywords: Ammonium; Mineralization; Nitrate; Nitrification; Soil depth; Soil nitrogen』

Introduction
Materials and methods
　Description of site
　Nutrient status history of site
　Climate
　Soil sampling and preparation
　Soil physico-chemical analyses
　Spiking experiments
　Statistical analysis
Results
　Physical and chemical characteristics of soils
　Changes in nitrate-N content with depth and treatment
　Changes in ammonium-N content with depth and treatment
　Changes in net mineralization with depth
　Changes in net nitrification with depth and treatment
　Changes in mineral-N contents with depth relative to soil C％
　N species transformations in relation to soil physico-chemical properties
Discussion
　Links to soil physico-chemical characteristics
　Origins of ammonium found at different depths
　What else might ammonium production per unit mass of C tell us?
　Observations on net nitrification
　Importance of N transformations at depth
Conclusions
Acknowledgments
References

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