Irrigation Scheduling of Maize Grown on a Vertisol Soil Under Changing Climate of Sofia’s Field

The purpose of this study is to evaluate the impact of climate uncertainties on maize irrigation requirements, grown on a Vertisol soil, Sofia’s field, Bulgaria. Through the validated WinIsareg model, four irrigation scheduling alternatives are simulated for the years of “very high“, “high“ and “average“ irrigation demands of past (1952–1984) and present (1970–2004) climate. Adaptation of irrigation scheduling to the present climate conditions during the “very dry“ years (P_I ≤12%) consists of an extension of the irrigation season by 15–20 days and a need of additional irrigation relative to alternative 1 and two irrigation events at alternatives 2 and 3. During the past climate alternatives 2 and 3 led to savings of 30 mm of water, while up to the current climate conditions the three irrigations alternatives should provide 360 mm of irrigation water. To obtain maximum yields in “dry“ (P_I = 12–30%) years, irrigation season should end by 05/09, as in the present climate, irrigation season has shifted about a week earlier for the three alternatives. In the “average“ (P_I = 30–60%) years the adaptation consist in accurately determination of the last allowed date for irrigation.