Water, Air, and Soil Pollution

, Volume 177, Issue 1, pp 335-347

First online:

Vegetation Type Affects the Relationship Between Soil Carbon to Nitrogen Ratio and Nitrogen Leaching

  • E. C. RoweAffiliated withCentre for Ecology and Hydrology, Orton Building Email author 
  • , C. D. EvansAffiliated withCentre for Ecology and Hydrology, Orton Building
  • , B. A. EmmettAffiliated withCentre for Ecology and Hydrology, Orton Building
  • , B. ReynoldsAffiliated withCentre for Ecology and Hydrology, Orton Building
  • , R. C. HelliwellAffiliated withMacaulay Institute
  • , M. C. CoullAffiliated withMacaulay Institute
  • , C. J. CurtisAffiliated withEnvironmental Change Research Centre, University College London

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Nitrate leaching occurs when the soil's nitrogen immobilisation and plant uptake capacity has been saturated. Several widely-used models of nitrogen saturation incorporate a breakthrough function in which N begins to be leached at C/N values below an upper threshold, and is completely leached at C/N values below a lower threshold. In a survey of deciduous and coniferous woodland, acid grassland and heathland sites for which both C/N and nitrate flux measurements were available, deciduous woodland and acid grassland typically had lower C/N ratios, and began leaching nitrate at a lower C/N ratio, than coniferous woodland and heathland. Least-square fits of nitrate breakthrough functions gave upper thresholds (no nitrate leaching) of 27 mol C mol−1 N for deciduous woodland and acid grassland and 50 mol C mol−1 N for coniferous woodland and heathland. Upper thresholds were similar, at 24 and 51 mol C mol−1 N, respectively, for total inorganic N (NH4 + NO3) leaching flux as a proportion of total inorganic N influx. In conifer plantations, stand maturity had a large effect, suggesting that a breakthrough function is unsuitable for modelling systems that are in disequilibrium. However, there was sufficient evidence to suggest that using different breakthrough C/N thresholds for different groups of vegetation would improve predictions of N saturation and leaching at both plot and catchment scales. The difference may be related to the reactivity of soil carbon; soils with a large proportion of recalcitrant carbon are likely to begin leaching nitrate at a higher C/N value than soils with more labile carbon.


deposition eutrophication forestry grassland heathland pollution retention