Risk to Onion (Allium cepa L.) Field Cultivation in Poland from Precipitation Deficiency

Abstract

The onion is the most common vegetable cultivated in Poland and yield is marked by high year to year variability. The yield quantity is predominantly affected by variable meteorological conditions, especially by precipitation deficiency. Data were collected from the Research Centre for Cultivar Testing and the Institute of Meteorology and Water Management for the period 1966-2005 to evaluate the effect of precipitation conditions on the yield of onions (Allium cepa L.) cultivated in Poland using multiple regression analysis. Verification of the curvilinear regression equation was conducted on the basis of relative forecast error and average relative forecast error. For this equation the ARFE amounted to 9.6%. The threshold precipitation value, i.e. the value at which reduction by at least 5% of the total yield occurs, was determined by curvilinear regression. Reduction of potential yield caused by precipitation deficiency and the frequency of precipitation deficiency were determined. Reductions of at least 5% in the average domestic onion yield in Poland occurred when atmospheric precipitation was ? 183 mm. This level of precipitation constituted 87% of the norm and took place in the period between the end of emergence to the beginning of leaf bending. Potential reduction in onion yield in Poland caused by precipitation deficiency in this period varied between 9 and 18%. In Poland, the frequency of atmospheric precipitation deficiency between 1966 to 2005 varied from 10% in the south-east to 50% in the central west and north west. The average frequency of atmospheric precipitation deficiency amounted to about 37%.