Impact of uncharacteristic weather conditions on the phenology and yield stability of spring barley (Hordeum vulgare L.) in Latvia: a 24-year study (2000–2023)

Climate change is one of the greatest challenges facing the agricultural sector in the 21st century. In recent decades, extreme heat, uncharacteristic for Latvia, prolonged drought, particularly in spring, and extremely heavy rainfall in the second half of summer have significantly impacted the development of cereals. An example is May 2023, which was the driest May in the history of observations in Latvia. The aim of the study was to describe how uncharacteristic weather conditions caused by climate change impact the phenology and yield stability of summer barley (Hordeum vulgare L.) in two distinct locations, Priekuli (climate type—Dfb) and Stende (climate type—Cfb), from 2000 to 2023. Spring barley in Latvia is usually sown in late April or early May. The analysis of the data revealed a moderately close relationship between the average air temperature in April and the barley sowing time in both Priekuli and Stende. For the most part, in years when the average air temperature in April has been higher, sowing has begun earlier. Early varieties typically require a minimum of 90 days from sowing to full maturity, whereas late varieties usually need an average of 100 to 110 days. However, in certain years, both early and late varieties have experienced a significantly shorter growing season. Years where the average air temperature during the growing season exceeds the norm typically witness a shorter growing season. This was the case, for example, in 2010, 2018, and 2021, when none of the varieties in Priekuli exceeded 89 days between sowing and full maturity. The data from the study show that if the transition from the vegetative growth phases to the generative growth phases occurred very rapidly, the plants had a low tillering rate, there were few productive stems, and the plants were short; hence, the yields were also low. For instance, in 2021, the variety ‘Ansis’ in Priekuli yielded 2.72 t ha-1, approximately twice as low as in years when the weather was optimal for development. If drought and heat accelerate the development of cereals, then frequent precipitation and lower air temperature during the ripening period hinder the onset of full ripeness. Observing adverse weather conditions, such as heavy rainfall, during the full ripeness stage delays harvesting and deteriorates crop quality, as demonstrated in 2017. Based on the results obtained, it is possible to select varieties and breeding lines that, regardless of the influence of weather conditions on the length of the growing season, maintain relatively high yield stability and good yield quality. An analysis of the 24-year data series shows that the increasingly frequent uncharacteristic weather conditions affect the phenology of spring barley. Furthermore, the study results do not show regional differences, as the impact of extreme weather conditions is similar at both observation locations.