Summary:

Irrigation needs of orchard plants in Poland are presented in the work using the formula N = P – Po (mm), where: N – water needs (mm) in a given pe-riod, P – actual rainfall (mm) in a given period, Po – optimum rainfall (water needs of plants). Optimum rainfall amounts according to modified schedule of Press [1963] for three ranges of air temperature in the particular months of the vegetation period were taken into consideration. Needs N were determined for 27 chosen meteorological stations, for five fruit trees' basic species as well as strawberries. The higher water needs for fruit trees were determined in central belt of Poland with north region of Szczecin as well as regions of Poznań, Płock and Słubice. These needs in the vegetation period with high temperatures ranged from 160 to 190 mm for plum trees, 140–171 mm for apple trees, 50–81 mm for pear trees as well as 39–73 mm for sweet and sour cherries. Advantageous mois-ture conditions were determined in both extreme belts of country, but also here irrigation needs were occurred in case of plum-trees and apple-trees. The highest rainfall deficits were detected in regions Białystok and Gdańsk in northern belt as well as Lublin and Puławy in south. Water deficits N were also calculated for irrigation periods for particular fruit tree species. It was found that the highest water deficits occurred in central belt of country, and the smallest – in south. In case of high temperatures of air, rainfall shortages in Land of Great Valleys were usually above 100 mm for apple trees, and they ranged from 73 to 108 mm for plum trees. The particularly large shortages of water were during the irrigation period in regions of Poznań, Szczecin and Kalisz. In case of advantageous rainfall schedule, one need would not set the irrigation of pear trees, sour cherry-trees and sweet cherry trees in whole south belt. The highest water deficits occurred in case of apples and plums ranging 50–75 mm, particularly in region of Lublin, the Puławy and Wroclaw. In northern belt of Poland the shortages of falls crossed 50 mm, coming to 82 mm in region of Białystok. The smallest shortages would concern plum-trees.