Summary:

The study was carried out in order to determine the frequency of droughts in the period of increased water needs of corn cultivated for grain in the region of Kujawsko-Pomorskie based on temporal variation of the standardized precipitation index SPI. Also were assessed the needs and expected productive effects of the plants grown under irrigation by a significant correlation between increases of yields of grain and the amount of rainfall. Rainfall data were derived from standard measurements of atmospheric precipitation during a period from 1 July and 31 August in the multi-annual period 1981-2010. These data were obtained from the branches of the Research Centre for Cultivar Testing (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 corn amounted to 26.7-40.0% in the region depended 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 corn which corresponded to periods of strong and moderate droughts (SPI ≤ -1.0) have been identified in 5 years of the 30 examined. The expected increase in the yield of corn grain cultivated on light soils under irrigation during those years exceeds 3.22 t.ha-1. In the 9 years occurred medium-level irrigation needs, which in the period of July-August, correspond to SPI values between 0 and -1.0.