The adverse effect of the long-term trend of the air temperature in Poland on the yield of onion

Abstract

The yield of onion in Poland is highly variable. The year-on-year variability depends mainly weather conditions, including the air temperature conditions. This research aimed to determine the effect of air temperature on the total yield of onion grown in arable farmland. Using multiple curvilinear regression analysis, the variability of yield was explained in 56% by the air temperature in the period ‘end of emergence - beginning of leaf bending’ and the linear trend (consecutive years in the 1966-2005 period). Based on this equation, the critical average temperature during the end of emergence-beginning of leaf bending (Ee-Blb) period was determined at 16.7oC, i.e. temperature followed by a reduction in the yield of onion by 5% compared to the long-term average. This decrease in the yield of onion caused by the occurrence of excessive air temperature also demonstrated spatial variability. In addition to high temperatures, the inclusion of the incidence of critical temperatures increased the diversity in the reduction in the yield of onions in Poland to < 3% and > 15%.