Grand challenges for the 21st century: what crop models can and can't (yet) do

Crop production is at the core of a 'perfect storm' encompassing the grand challenges of achieving food and nutrition security for all, in the face of climate change, while avoiding further conversion of natural habitats for agriculture and loss of biodiversity. Here, we explore current trends in crop modelling related to these grand challenges by reflecting on research presented at the Second International Crop Modelling Symposium (iCropM2020). A keyword search in the book of abstracts of the symposium revealed a strong focus on 'climate change', 'adaptation' and 'impact assessment' and much less on 'food security' or 'policy'. Most research focused on field-level investigations and far fewer on farm(ing) systems levels - the levels at which management decisions are made by farmers. Experimentation is key to development and testing of crop models, yet the term 'simulation' outweighed by far the terms 'experiments' and 'trials', and few contributions dealt with model improvement. Cereals are intensively researched, whereas roots, tubers and tropical perennials are under-researched. Little attention is paid to nutrient limitations apart from nitrogen or to pests and diseases. The aforementioned aspects represent opportunities for future research where crop models can help in devising hypotheses and driving new experimentation. We must also ensure that crop models are fit for their intended purposes, especially if they are to provide advice to policymakers. The latter, together with cross-scale and interdisciplinary efforts with direct engagement of stakeholders are needed to address the grand challenges faced by food and agricultural systems in the next century.