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Modelling N mineralisation - NT1519

Existing models of carbon (C) and nitrogen (N) mineralisation divide soil organic matter amongst several compartments of distinct (and constant) turnover rate (reflected in so-called k values). These rates are not well suited to simulating seasonal fluxes of N as they tend to be too long. Also, because the conceptual basis for their division is chemical degradability, no satisfactory procedures have been found to measure or characterise them. The latter feature means such models are relatively un-constrained during parameterisation, increasing the uncertainty attached to selected values. The objective is to improve simulation of N and C mineralisiation, and ultimately incorporate a new, more robust mineralisation model into a system-based structure, such as the fertiliser recommendation system SUNDIAL. We will use our organic matter fractionation procedure in conjunction with a mechanistic approach to further the objective. A mechanistic model defines soil organic matter compartments by their function, which in our scheme equates to physical location (between and within aggregates, and on the surfaces of primary particles). Density fractionation (Sohi et l, 1998) provides an experimental basis for their separation, permitting instantaneous assessment of isotopic composition (and hence-using tracers-dynamics) by mass spectroscopy. To generate data for parameterisation, we will alter the isotopic composition of `free` (between aggregate) organic matter in a sandy soil by adding labelled maize straw. Subsequent changes in the isotope ratio of this compartment, and two other compartments separated by the fractionation procedure (intra-aggregate and organomineral) will be measured by mass spectroscopy. These measurements will provide a relatively high level of constraint in model parameterisation.
Time-Scale and Cost
From: 1998

To: 1999

Cost: £60,367
Contractor / Funded Organisations
Rothamsted Research (BBSRC)
Fields of Study
Fertilisers and Nitrate Pollution