Summary:

The data on the yield of potatoes grown on very good and good wheat soil complex as well as very good and good rye soil complexes in 11 experimental stations of varieties evaluation in 1996-2005 were used in this paper. For the wheat and rye soil complexes models of medium early as well as and medium-late and late potato crop were constructed as regression functions (quadratic polynomial with interactions), in which the amount of precipitation in May-June and July-August were independent variables. Models were studied in the range of 75-175 mm precipitation in May-June, and 90-220 mm precipitation in July-August, which corresponds to the average ± standard deviation of these parameters.In all cases, July-August precipitation was the factor more strongly affecting the yield. For medium early potatoes grown on wheat soils the optimum for obtaining the highest yields proved to be the set of factor: low May-June precipi-tation (88 mm) appeared with high July-August precipitation (217 mm). The yield achieved under these conditions amounted to 594 dt•ha-1. Medium late and late potatoes grown on the same soil reacted similarly to water from rain - the optimum set of factors was: May-June precipitation - 76 mm and July-August - 220 mm, giving a yield of 643 dt•ha-1.Medium early potatoes grown on rye soils had the highest yield (481 dt•ha-1) when the May-June precipitation was above average (143 mm) and July-August one was high (220 mm). Medium late and late potatoes on these soils gave the maximum yield (512 dt•ha-1) in similar conditions - 140 and 220 mm of precipita-tion respectively. The lowest yields were associated with low rainfall in May-June (75 mm) and in July-August (90 mm) for both groups of earliness and both: rye and wheat soil complexes. By examining similar models of the percentage of starch in potato tubers it was noted that this parameter depended mainly on precipitation in July and August, which stronger affected on rye than wheat soil complexes.