Re-evaluating temperature thresholds for growth and nutrient uptake in winter cereals in Estonia: a review of air-soil temperature dynamics

This study re-evaluates the agronomic validity of temperature thresholds for cereal growth and nutrient uptake in cool-temperate agroclimates. By integrating a physiological review with a spatiotemporal analysis of Estonian air temperature records (1965–2024), we assess the potential for phenological mismatch between atmospheric warming and soil thermal readiness. Our analysis reveals a significant advancement in the onset of the thermal growing season, particularly in South-Eastern Estonia, where spring now begins approximately 10 days earlier compared to the 1965–1990 baseline. Synthesizing these trends with established principles of soil thermal inertia, we identify a potential increase in the risk of ‘false springs’, where atmospheric signals trigger vegetative growth while soil conditions remain restrictive. Published evidence indicates that nutrient uptake is kinetically constrained in cool soils: nitrogen uptake becomes effective only at soil temperatures of +8–10 °C, and phosphorus uptake is critically limited by low diffusion rates and suppressed mycorrhizal activity, whereas potassium uptake is comparatively less sensitive. We suggest that under increasingly variable climatic conditions, relying solely on the standard +5 °C air temperature threshold may lead to premature fertilisation and nutrient losses. Therefore, agronomic decision-making in Northern Europe may need to increasingly account for the hysteresis between rapid atmospheric warming and slower soil thermal activation.