We examined the change of the time of water balance of soil in long-term experiment, on chernozem soil, in different croprotation systems (mono-, bi- and triculture). We found the smallest difference between the water deficit of not irrigated and irrigated plots in triculture. We concluded that irrigation impressed favourably on water balance of soil in both of crop-rotation systems. Water deficit has decreased significantly after irrigation in 25. May in mono- and triculture. Irrigation moderated only values of water deficit. Irrigation in 30. June not influenced water balance of soil in both of crop-rotation because of a big drought. Water deficit of soil lessed till harvestperiod because of rainy season at the end of August and in September.