The objective of the study is to define the optimal irrigation mode for cotton-plant in the south of Ukraine considering environmental protection. The vegetation period of cotton-plant was divided into three intervals: emergence – 50 % of budding; 50 % of budding – 50 % of flowering; 50 % of flowering – 50 % of maturation. The experiment provided six variants of irrigation mode: 1) without irrigation; 2) 70 (% FC)-60-without irrigation; 3) 70-60-60; 4) 80-60-60; 5) 70-70-70; 6) 60-70-60. Yield data reveals that the greatest effect on irrigation was obtained in the first vegetation interval at 80 % FC and 70 % FC by irrigation rate of 350 m³/ha and 500 m³/ha and subsequent maintaining the content of soil moisture higher than 60 % FC. The yield of raw cotton before the frost (from the beginning of maturation to the first frost) increased by 0.49-0.55 t/ha and was 1.59-1.65 t/ha at LSD05 = 0.41 t/ha. The optimal irrigation rate in the south of Ukraine should be 1000-1500 m³/ha. While reducing moisture content to 70 % FC in the phase of flowering and fruitification of cotton-plant, irrigation delays the plant development by 5-6 days and enables intensive vegetation growth increasing the yield after the frost. The total yield reduces to 1.75 t/ha in contrast with 2.00 t/ha at maintaining 60 % FC in the second and third intervals of cotton-plant vegetation.
Keywords: irrigation rate, cotton-plant, vegetation period, flowering, fruitification, fiber, oil, environmental safety.
