The objective of the study was to substantiate the methods to determine irrigation requirements for agricultural crops under drip irrigation. According to the first method, the values of water consumption deficits should be determined by meteorological parameters for continuous number of years (more than 25 years), and the rated year should be chosen. After the rated year has been chosen (for drip irrigation 5 % of probability), the water consumption deficits are calculated by intra vegetation periods. The paper results the calculation of the water consumption deficits for orchards in Semikarakorsk for extremely dry year. Tree planting scheme is 6×4 m². Region of plant alimentation is 24 m². Two emitters discharging 6 liters per hour are required to irrigate one tree. Area wetted is 3.14 m². The calculation was done for medium loamy soils. Field capacity is 320 mm. Irrigation requirements for extremely dry year was 1.794 m³ per one tree, or 747 m³/ha. According to the second method of fictitious rated year, the average annual values of meteorological factors should be available. Using those factors, water consumption deficits for intra vegetation periods are calculated, deficits for a given crop are summarized, and finally irrigation requirements for average longterm conditions are obtained. To determine irrigation requirements for the year of a given probability, irrigation requirements for average long-term conditions should be multiplied by the modular coefficient. Irrigation requirements for average long-term conditions were 1.204 m³ per one tree, or 501.7 m³/ha.
