Summary:

The study was carried out in order to determine the frequency of droughts in the period of increased water needs in potato, and to assess the needs and expected productive effects of the plants grown under irrigation on the basis of temporal variation of the standardized precipitation index SPI in the Kujawsko-Pomorskie district. Rainfall data were derived from standard measurements of atmospheric precipitation in between 1 July and 31 August in the multi-annual period 1981-2010.These data were obtained from the branches of COBORU in Chrząstowo, Głębokie and Głodowo, and the University of Technology and Life Sciences Research Centre in Mochełek. The results of carried research showed that the frequency of occurrence of dry spell during the period of increased needs for water of potato amounted to 26.7-40.0% in the region, depending on the locality. Strong droughts occurred in the year 1983, 1989, 1992 and 1994, moderate drought in 2005 and weak droughts in 1982, 1984 and 1999. Great irrigation needs of potato which corresponded to periods of strong and moderate droughts (SPI ≤ -1.0) have been identified in 5 years of the 30 years examined. The expected increase in the yield of potato tubers grown on light soils under irrigation during those years exceeded 15.7t.ha-1. In the 9 years of the 30 have occurred medium-level irrigation needs, which in the period of July-August, corresponded to SPI values between 0 and -1.0.