THE RELATION BETWEEN ADVERSE THERMAL SOIL CONDITIONS AND VARIABILITY OF YIELD OF ONIONS (ALLIUM CEPA L.) IN ARABLE FARMLAND IN POLAND

摘要

Edaphic conditions at the root zone are important not only for the growth and development of onions, but they also determine yield. Soil temperature, in contrast to other indicators used in agro-meteorological research, reflects an entire complex of meteorological conditions in combination with soil conditions. The aim of this study was to evaluate a decrease in yield of onion grown in arable farmland in Poland caused by adverse soil thermal conditions. To achieve this goal, we used data from 17 COBORU experimental sites and 47 meteorological stations concerning phenological and agronomic dates, the yield of onions, and soil temperature during the growing season over the period 1966-2005. In Poland, a decrease in the yield of onions of at least 5% occurs when the average soil temperature during the period “end of emergence-beginning of leaf bending” (Ee-Blb) exceeds 18.8°C. In 1992, the least favourable year for onion yield in the period 1966 to 2005, soil temperatures in most parts of the country ranged from 19.0°C to over 22.0°C; the highest being in central-western Poland. The greatest decrease in onion yield due to both excessive temperatures and a too frequent incidence of these temperatures, is observed in the central-western part of the country, the south-eastern area of Poland and around the area of Warsaw, where the average annual onion yield may be reduced by more than 15% compared to the long-term average.