NDICEA Calibration and validation on a northern UK soil

Abstract

Modelling nitrogen (N) dynamics in agricultural soils can improve our understanding of the nitrogen cycle in rotational systems. NDICEA (Nitrogen Dynamics in Crop rotations in Ecological Agriculture) is a tool to model soil N dynamics for maximum nitrogen use efficiency (NUE) and minimum environmental impacts from agricultural fertilization. In this study the model was calibrated using actual soil mineral N data from 2 years of a long-term organic versus conventional systems comparison trial. Calibration data was used from only the organic crop protection treatments for an organic crop rotation under (a) organic fertility management (ORG-OF) and (b) conventional fertility management (ORG-CF), and a conventional crop rotation under (c) organic fertility management (CON-OF), and (d) conventional fertility management (CON-CF). The model was subsequently validated using the same four treatment combinations from the conventional crop protection treatments. The accuracy of soil mineral N predictions was consistently improved after calibration, with the model performing best under organic fertilization regimes; reflecting the model’s original purpose. The lack of difference among treatments for the calibrated soil parameters demonstrated that the calibration procedure was robust and could result in a model that is superior to the non-calibrated one, and specific for this soil type, regardless of soil management practices. The simplification of complex biological processes into model parameters limits the use of NDICEA as a tool to explain the underlying processes driving soil N dynamics. Nevertheless it could be a useful tool for visualising field-scale N dynamics, allowing farmers and advisors to explore the impact of changing management factors on within-field N efficiency.