The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 229

Fig. 4.1.2. Ratio of gross nitrification/NH 4 + immobilization for soils sampled in autumn 1997; the
sandy loam soils were sampled before and after cultivation.
Conclusion
Gross N transformation data can be used to examine specific pathways of
the soil N cycle in greater detail than was previously possible. Such data can
also be used to study the dominant processes 'consuming' NH 4 + in soil.
This may lead to an indicator of potential N loss or degree of 'N saturation'.
This indicator seems to be appropriate for use in arable soils, with careful
interpretation, as well as in forested systems. However, the range of values
for this ratio indicating low, medium or high potentials for N loss (or 'N
saturation') still needs to be defined. To achieve this, additional data sets
are being obtained from our ongoing research.
Apart from the relative dominance of each N pathway in a soil, the
actual amount of N loss will also depend on the size of the NO 3 − pool, soil
physical properties, climate and any direct losses from fertilizer or manure.
Integrated use of measurements, indices and modelling approaches in
the prediction of N loss is likely to give the best results, with the actual
combination of measurements and models determined by the specific
questions to be answered.
Acknowledgements
We would like to thank Maureen Birdsey and Wendy Wilmer for 15 N
analysis. This work was partially funded by the UK Ministry of Agricul-
ture, Fisheries and Food, the German Ministry for the Environment
and the Open University Research Fund. IACR-Rothamsted receives
grant-aided support from the Biotechnological and Biological Sciences
Research Council.