1. Introduction

Miterra is a deterministic model to simulate integrated flows and emissions of nutrient elements at various geographical scales. The model was originally developed as a regional model, named Miterra-Europe, to assess the effects and interactions of policies and measures in agriculture on N losses on a NUTS (Nomenclature of Territorial Units for Statistics) 2 level for all member states of the European Union (EU) ( Velthof et al., 2009; de Vries et al., 2011, Velthof et al., 2014). In recent projects, Miterra-Farm, a farm-level version of the Miterra model, was adapted using the same approaches of the European version, to estimate emissions and assess mitigation measures at farm scale ( Duan et al., 2023).

In general, the Miterra model can estimate:

Atmospheric emissions of ammonia (NH₃), nitrous oxide (N₂O), nitrogen oxides (NO_x), and methane (CH₄) from manure management and fertilization;
Surface runoff and leaching of N & P to the ground- and surface waters;
Turnover and sequestration of soil organic C and N;
Balance of other nutrient elements: S, K, Na, Ca & Mg; and
Balance of soil heavy metals (Cd, Cu & Zn).

Miterra can also model a suite of mitigation measures, and can be used to assess the effects of different management strategies and policies at farm, national, or European level.

The Miterra model comprises a comprehensive, collated input database on European climate and soil data, livestock numbers, land use, crop areas and yields, nutrient inputs and outputs, and emission factors for greenhouse gas emissions, and runoff and leaching factors for N. The model calculations are primarily based on emission factors, but also include processed-based algorithms from other models such as INTEGRATOR, RothC, and ALFAM2.

Model structure

The Miterra model can be roughly divided into 2 main components ( Figure 1.1): one capturing the flows in and emissions from the livestock sector, and the other representing the processes in the soil and the cropping sector.

In the livestock sector, N content in livestock excretions in both solid and liquid forms during housing, farmyard, storage, and grazing periods are calculated. Gaseous N emissions, including NH₃, N₂O, and NO_x, as well as N losses to water during storage, are estimated using emission factors. Ex-storage manure and excretions during grazing are distributed to the soil as organic fertilisers.

Other nutrient inputs to soil include minerla fertilisers, crop residues, atmospheric depositions, and biological N fixation. In the soil, the uptake of nutrient elements by crop, emissions to the atmosphere, runoff and leaching to surface water and groundwater, and the turnover of soil organic matters are calculated by the model to produce a detailed budget of nutrient input, output, and balance.

Figure 1.1: Shematic illustration of the Miterra model showing the flow direction of nutrient elements.

Miterra was originally developed to focus on the flows of C, N, and P. Recent development has included processes to model other elements, such as S, K, Na, Ca, and Mg, as well as heavy metals Cd, Cu, and Zn. The flows of most elements are modelled independent of each other, except for the turnover of organic C and N, which are coupled via C:N ratios.