The data on sugar beet yield were taken from Stations of Cultivar Assess-ment situated in south-west Poland. Using the method of multiple regression with interactions, models of root and leaf yield and sugar content percentage were con-structed, where the independent variables were precipitation total in the periods April-June and July-September or the number of days with rainfall in the stated periods. The optimum for obtaining highest yields of beetroots proved to be the set of factors: rainfall April-June 222 mm (the highest studied) and rainfall July-September 260 mm (a bit higher than average). As regards the number of days with rainfall, the optimum values were 35 days in the period IV-VI (values lower than average) and 50 days in VII-IX (value close to the maximal studied). The yield of roots was lowest with the lowest precipitation totals in both the periods (122 and 152 mm), and also when the highest number of days with rainfall in the spring season (46) was accompanied by low number of days with rainfall in the summer period (33).
For the yield of leaves the best set of factors proved to be the maximum precipitation totals studied, both those of the spring and summer period (222 and 322 mm, respectively) and the maximum number of days with rainfall in both the periods (46 and 55). The least favorable sets, both for the model with precipitation total and the one with number of days with rainfall, proved to be the highest values of the independent variables in the period IV-VI (222 mm and 46 days, respectively), and the lowest (122 mm and 33 days, respectively) in the period VII-IX.
Sugar content in sugar beetroots was highest with low (149 mm) spring precipitation and minimum summer precipitation (152 mm). The optimum, from the point of view of that parameter, number of days with rainfall in IV-VI was 46 days (maximal studied) and in VII-IX - 33 days (minimal studied). However, sugar content was smallest with lowest precipitation of the spring period and highest of the summer period, and maximum number of days with rainfall in both the periods.
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