Evaluating the transition of marginal grasslands to arable systems for human-protein production through an in silico long-term experiment

The shift from livestock grazing to arable cropping systems is increasingly proposed to enhance protein production efficiency in temperate agricultural landscapes. However, for such transitions to support food security goals, the resulting grain must meet the crude protein content (PC) threshold set by the food industry of ≥13%. Through model simulations, we investigated the effects of nitrogen (N) fertilization rate, cultivar, sowing date, and late fertilization on wheat grain quality under variable climatic conditions at the North Wyke Farm Platform in southwest England, UK. While this region offers one of the UK's most favourable climates for wheat yield potential, its marginal soils pose significant agronomic constraints. Using a process-based modelling framework, we conducted 5028 simulations combining six fertilization levels (0–200 kg N/ha), four wheat cultivars (Claire, Conquest, Dekan, Option), two late fertilization levels (0 or 20 kg N/ha), and three sowing dates (late September to late October), covering 1984–2021. The food industry PC threshold was reached in only 36% of simulations. Fertilization was the most influential factor, followed by cultivar, late nitrogen application, and sowing date. Post-processing the simulations with a regression tree analysis showed that the 13% PC threshold was only frequently achieved with ≥160 kg N/ha, early sowing, and when the cultivars Dekan or Conquest were used. Given current UK fertilization practices, typically