Weather conditions outside growing season very important

Winter important for cereal yield

“Our continuous field trials in Dürnast near Freising (Bavaria) have provided a very comprehensive archive of data for studying the relationships between climate change and yields,” explains first author, Dr. Kurt Heil. The soil available here consists of very fertile Pleistocene Loess.

Previous studies on the influence of the weather conditions on agricultural yields have focused almost exclusively on the influence of the water supply (drought stress) and temperature (heat) during the growing season. In their study, Dr. Kurt Heil and his team at the Chair of Plant Nutrition have looked at the weather parameters outside the growing season – a topic to have received less attention to date.

“Late frosts can sometimes occur in our area as late as May,” explains Heil. As winter periods end earlier nowadays on a perennial average, late frosts of this kind have a significant impact on plant health, as the plant already begins to grow at a temperature of a few plus degrees, so the young shoots are damaged by late frosts.

With higher rates of nitrogen fertilization, however, weather patterns become increasingly significant during growing seasons, which has also caused plants to become more sensitive to extreme weather conditions. When more fertilizer is used, plants grow more strongly, which means they consume more water and in the absence of precipitation are hit harder by drought than they are when they grow less strongly.

“Temperature and precipitation are of importance with all calculations in all variants, but to a lesser extent when they are considered as totals or averages. Specific indices such as frost change days, temperature thresholds, the precipitation intensity, rain-free days, the early or late frost index and the drought index are of greater relevance in this context,” explains Urs Schmidhalter, Professor of Plant Nutrition at TUM.

In the study, the annual variations in crop yields were largely determined by the prevailing climatic conditions in the winter as well as by the transition periods from the warmer season to the winter and vice versa. According to the study, indices such as temperature thresholds, frost change days and precipitation intensity are particularly important in the winter. During the main growing seasons, it was only the intensity of the rainfall that was of considerable importance.

“These results can be attributed to the high availability of the available field water capacity at this location, which significantly reduces the need for summer precipitation when the stores of groundwater are replenished in the winter,” says Heil.

Overall, the results expand the range of the potential effects of climate change and are transferable to high-yield locations in Western Europe, which are among the world’s most fertile and high-yield places of cultivation and therefore predestined and important for food production. The continuation of long-term experiments also suggests essential insights and predictions concerning the effects of climate change in the future.