Summary:

The aim of the study was to compare the water requirements and the precipitation deficiencies during cultivation of asparagus in the period from June to August in the regions of Bydgoszcz and Wroclaw. The water needs were calculated using the plant coefficient. The reference evapotranspiration was measured by Grabarczyk's method (1976). The coefficients kc, determined for the Polish conditions by Rolbiecki (2013), were used to estimate the water requirements considered as the crop evapotranspiration. In the studied period (from June to August, 1996-2015), higher water requirements of asparagus were noted in the Wroclaw region (366.1 mm) than in the Bydgoszcz region (288.5 mm). The monthly water needs in June, July and August were 69.8 mm, 128.8 mm and 167.5 mm, respectively, in the Wroclaw region, and 55.5 mm, 98.5 mm and 134.5 mm, respectively, in the Bydgoszcz region. In July, the tendency to increase the water requirements in both observed regions was noted. The monthly crop evapotranspiration in July rose in each decade by 12.3 mm in the Bydgoszcz region and by 21.2 mm in the Wroclaw region. In the 20-year study, the rainfall deficit in June and July during 11-13 years was noted. In August, the precipitation deficiencies were observed during 16 years in the Bydgoszcz region and during 19 years in the Wroclaw region. A higher rainfall deficit during the 20-year period under study was reported in the Wroclaw region (128.5 mm) than in the Bydgoszcz region (87.0 mm). In August, the highest monthly precipitation deficiencies of 100.3 mm (Wroclaw region) and 70.3 mm (Bydgoszcz region) were noted.