Modeling crown temperature of winter sugar beet and its application in risk assessment for frost killing in Central Europe

Abstract

The cultivation of sugar beet as a winter crop in Central Europe will require tolerance of severe frost. Due to the large variation of survival rates in different environments it is necessary to quantify the risk of frost killing for potential growing regions. The objectives of our study were, (i) to determine the lethal temperature of sugar beet taproot crown tissue as an indicator of frost damage, (ii) the development of a regression model that properly estimates the temperature of crown tissue from standard weather data, and (iii) a risk assessment for frost killing in four beet cultivation regions, representing different climatic conditions in Central Europe. In field trials at six environments, temperatures were measured above the beet canopy (0.3–0.5m height), at the soil surface, 5cm deep in the soil, and in the taproot crown. Survival rates were determined after winter.The survival rates of sugar beets were highly dependant on the maximum taproot diameter (optimal size: 1–2.5cm) and the environmental conditions. A crown tissue temperature below −6°C was a reliable indicator for frost killing, even though the exact lethal temperature of optimal sized sugar beets could not be identified. The crown temperature was accurately predicted from available weather data using multiple linear regression models. It was estimated best by combining the parameters ‘daily mean air temperature’, ‘daily mean soil temperature at 5cm depth’ (closest correlation to crown temperature) and ‘daily snow depth’. The prediction was further improved by adding the air and soil temperatures of the previous day and the 2-fold interactions of regressors to the model.Risk assessment for frost killing in Central European beet growing areas was based on weather data of the past 20 years provided by Germany's National Meteorological Service (Deutscher Wetterdienst, DWD). Our approach showed that at locations with mild winters, such as Cologne, the successful cultivation of winter sugar beet is possible with little risk of frost killing. On the contrary, growing winter sugar beet at places like Göttingen and Regensburg holds a high risk for frost killing. Finally, the presented approach needs to be improved with more accurate estimates of crown tissue temperature, and more precise determination of the lethal temperature of winter beets with the optimal taproot diameter.