Combining micro-bottom-up and macro-top-down modelling responses to nutrient cycles in complex agricultural systems

Concerns over the long-term sustainability of the food production system and the nutritional content of food from mineral depleted soils have encouraged a policy shift to sustainable agricultural practices where soil health supports nutrition-sensitive agriculture. Interventions at the micro scale have the ability to affect the entire system, forcing an examination at the whole of systems level. Modelling plays an important role in determining the outcomes of policy intervention combinations, particularly when systems are identified as being complex. This study begins with a systems map tracing the nutrient cycling process between natural ecosystem processes and farm practices from the bottom-up within a top-down framework. Soil is at the centre of this approach, expanding links to other influences within the framework in order to understand the relationships between elements in an environmental-agricultural system. Moving to a generic model from a broad conceptual system map is problematic when crop types, plant mineral absorption rates, soil and geographic differences are to be accommodated. Work has been done to develop top-down framework models integrating bottom-up component models, capable of being used in different scenarios. Whether existing models are used or new models are created, this study recommends that an appropriate modelling response require examination of systems and policy interventions both holistically and in detail encompassing situational specifics.