The paper defines the effect of plant development stages and the length of agrophenological periods on late potato cultivars yielding over 1972-1995. An attempt has been made to determine a decrease in the potato yield due to delayed planting and emergence and flowering dates. This relationship was described with the analysis of concentration and the analysis of single regression and multiple linear regression using the program STATISTICA 5. Potato yielding was most negatively affected by emergence date. A ten-day delay in emergence, as compared with an average, can decrease the yield from 15% in the central and central-and-western Poland to 25% in the north-eastern part. A ten-day delay in the planting, emergence and flowering dates is most often recorded in the east of the country and least frequently – in the central-western part of the country.

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