Summary:

The aim of this study was to determine the average early potato numerical irrigation needs, displaying their large variability in time and linking those needs with the projected increases in tubers yield under the influence of the applied pro-cedure. In the study a new research method was used, based on the results of many years of strict field experiments conducted at various research centers in the areas of particular shortage of water used for agriculture. These areas include light and very light soils located in the central part of Polish lowland, in the rainfall area during the growing season (IV-IX) limited with the isopluvial line 350 mm. The needs of irrigation were calculated for four places (Szczecin, Bydgoszcz, Poznań, Warszawa) located within the areas of particular water deficit. Precipitation data from the years 1971-2005 derived from measurements of our own and Institute of Meteorology and Water Management were used in the calculations. It was found that the need for irrigation of the potato as a basic yield-forming factor, on very light soil with a drained subsoil, occurs in areas of water deficits in the 80-86% of the years, depending on the locality. In the 20-40 % of the years the needs are high and their cover brings the yield increase by at least 17.0 t•ha-1. On light soils with a dense subsoil the need for irrigation of potatos as a supplemental (emergency) action occurs in areas of particular shortage of water in the 71-89% of the years, depending on the locality. In the 8-20% of the years the needs are high and their cover brings the yield increase by at least 18.0 t•ha-1. It was also shown that the irrigation needs of potato, which change over years in places located within areas particularly water shortage, did not indicate significant trends in the period 1971-2005.