The challenges – and some solutions – to process-based modelling of grazed agricultural systems

Authors: SNOW, V - Ag Research Limited; Rotz, Clarence - Al; MOORE, A - Commonwealth Scientific And Industrial Research Organisation (CSIRO); MARTIN-CLOUAIRE, R - Institut National De La Recherche Agronomique (INRA); JOHNSON, I - University Of Melbourne; HUTCHINGS, N - Aarhus University; ECKARD, R - University Of Melbourne

Submitted to: Journal of Environmental Modeling and Software
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2014
Publication Date: 4/21/2014
Citation: Snow, V.O., Rotz, C.A., Moore, A.D., Martin-Clouaire, R., Johnson, I.R., Hutchings, N.J., Eckard, R.J. 2014. The challenges – and some solutions – to process-based modelling of grazed agricultural systems. Journal of Environmental Modeling and Software. DOI: 10.1016/j.envsoft.2014.03.009.

Interpretive Summary: Grasslands occupy 25% of the terrestrial surface or about 70% of the world’s agricultural land. They contribute to the livelihoods of over 800 million people and so have an important role to play in satisfying the increasing demand for high-quality protein. Given their extent, grasslands are a crucial system to consider when evaluating local or global issues related to sustainable management, especially in the face of on-going land-use changes and climatic uncertainty. Agricultural systems that include grazing animals are characterised by a number of features which present challenges to the experimentation and understanding of these systems. Because of the many components and interactions of pastoral systems, it is important to consider the management of the grazed system from a whole-farm perspective. Robust and flexible process-based simulation models of pastoral and integrated systems are needed to investigate the adaptation of production systems to increase productivity, decrease environmental effects, assist understanding of climate change issues, and to meet the demand of farmers for a better quality of life. We have reviewed six simulation models against the key challenges for modelling the additional complexity that pastoral systems face compared to arable systems. We have placed particular emphasis on the range of possible solutions with the point of view that diversity will give flexibility of future use. We find that in most cases there is a diversity of solutions incorporated into the models reviewed and that there is the potential to capture additional diversity, if needed, from other models provided the software and legal constraints are not too onerous. We also note an apparent lack of development in the modelling of the effects of extreme events, systematic animal-mediated nutrient transfers, pests, weeds and gene-environment interactions in pastoral simulation models and suggest that these subject areas should receive more attention.

Technical Abstract: Pastoral systems are characterised by a number of features, not present in arable cropping systems, which present significant challenges to the simulation modelling of pastoral systems. These challenges include: (i) pastures are biologically diverse so interactions between plant species must be considered; (ii) economic return requires the inclusion of the animal as an additional tropic level; (iii) interaction between the grazing animal and the pasture is complex, influenced by the environment, plant species and animal behaviour and this creates feedbacks that can result in vicious cycles; (iv) animals spatially transfer substantial amounts of nutrients both randomly and systematically and this create or exacerbate soil variability; and (v) whole farm management is both more complex and more important to system function in grazed compared to arable systems and it is harder to capture in simulation models. These challenges complicate the process-based modelling of pastoral systems and present significant challenges to model developers and users. We discuss these challenges, describe the range of solutions used by different models and discuss the strengths and weaknesses of these solutions. We have placed particular emphasis on the analysis of a range of possible solutions with the point of view that diversity between and within models is important to provide the flexibility needed for future uses. We find that for most challenges there is a diversity of solutions incorporated into the models and that there is the potential to capture additional diversity, if needed, from other models. We note an apparent lack of development in the modelling of extreme events, systematic animal-mediated nutrient transfers, pests, weeds and gene-environment interactions in pastoral simulation models and suggest that these subject areas should receive more attention.