S15 - Session P3 - Soil temperature increases by ca. 1.1°K in a fruit orchard due to climate change – results of 50 year records

Authors: Achim Kunz, Michael Blanke *

Soils are a buffer in terms of climate change- like oceans. The vast majority of climate change studies concentrate on effects on plants, thereby neglecting the changes brought about in the soil. For the majority of our horticultural crops, soil acts as growing substrate. The soil in this experiment is a luvisol (pH 6.8) on loess at Klein-Altendorf (50° N) near, Bonn, Germany. Changes in the soil are slow, thereby requiring long term observations. Hence, the objective is to investigate changes in soil temperature in 20 cm depth (as compared with air temperatures) based on 60 years records with the following results: 1) Over the last 60 years, the annual air temperature at Klein-Altendorf, Germany increased from 8.6 °C in 1958 to 10.3 °C in 2018 and similarly in the vegetation period (1 April- 30 October) from 13.7 °C in 1958 to 15.2 °C in 2018, i.e.in both cases by ca. 1.6°C. 2) Two distinct phases could be distinguished, one without significant temperature increase from 1956-1988 and one with a pronounced increase from 1989 onwards. 3) The summer soil temperature increased by 1.2°C compared with a larger increase of 1.6°C in the winter, using linear curve fitting. When the two phases were compared, the summer soil temperatures increased from 15.5 °C in phase I (1958-1987) to 16.4°C, i.e. a rise by 0.9°C over 60 years. In the winter, the soil temperature changed from 4.6°C to 5.8°C, equivalent to a rise of 1.2°C. The stronger increase in winter temperatures (air and soil both by +1.2 °C) than in the summer (air +1.0 °C; soil +0.9°C) may affect winter chill, bud break and forcing of the fruit trees. 4) The largest increase in soil temperature was in the winter months January to March.