Summary:

Two soil profiles at Kruszyn Krajeński near Bydgoszcz were studied at the paper. Characteristic of soils and their water properties were determined. Air temperature (t) values and rainfall amounts (P) in particular months of vegetation period (April–September) in 1997–2006 for the investigated area were given. The vegetation period was characterized by mean air temperature 14,4 °C, ranging in particular years from 13,4 to 15,2 °C. Rainfall total during the vegetation period amounted on average 283,4 mm, ranging from 177,5 to 377 mm. Potential evapotranspiration (Etp) amounts were also determined using Grabarczyk’s formula. Irrigation requirements under the considered soil-climatic conditions were determined according to the following Drupka’s proposal: rainfall total (P) in the vegetation period as well as potential evapotranspiration (Etp) and difference Etp – P. Irrigation is needed when rainfall is lower than 370 mm, Etp is higher than 515 mm, and difference Etp – P is higher than 150 mm. On the base of rainfall amounts in vegetation period it can be stated that in years 1997-2006 irrigation requirements have been occurred in 8 seasons, and in two remaining years irrigation also could be needed because rainfall amounts were slightly higher from 370 mm (only by 4 and 7 mm, respectively). Potential evapotranspiration (Etp) in the vegetation period calculated according to Grabarczyk’s formula was higher than 515 mm in 9 seasons, and in case of the three years (2002, 2003, 2006) it was even higher than 700 mm. In all the considered years, the Etp – P difference was higher than 200 mm that indicated needs of irrigation. Optimal rainfall amounts for sugar beet were determined according to Klatt and Press proposals. Expected sugar beet root yield increases due to sprinkler irrigation which could be obtained in 1997-2006 were estimated using another Grabarczyk’s formula modyfied by Rzekanowski at al. These yield increases amounted on average 20 t*ha^-1, ranging from 4,16 t*ha^-1 to 36,6 t*ha^-1 in particular seasons, as dependent on rainfall amounts during critical periods of enhanced water needs of sugar beet.