CONSERVING OF THE RESOURCES
The region of Varna proved to be a driest in terms of precipitation in this country. Trend test applied to climate datasets reviled a significant increase for seasonal reference evapotranspiration ETo during 1970-2004. Detected climate variability&droughts create uncertainties for maize irrigation scheduling and harvested yield. To cope with them, simulations have been performed for past (1951- 1984) and present (1951-2004) weather conditions using the validated water balance WinISAREG simulation model for two maize hybrids of different sensitivity to water stress grown on a Haplic Chernozem soil of medium water holding capacity. The study compares three irrigation scheduling alternatives built in agreement with past studies to develop environmentally sound/water saving irrigation technologies that consist of refilling the soil reservoir by adopting a management-allowed depletion fraction (MAD): (1) MAD=0.50; (2) MAD=0.33; (3) MAD=0.50 but partially refilling the soil reservoir. Simulations relative to the very high irrigation demand year of the current weather show that when aiming at maximum yield all three scheduling alternatives require the same irrigation depths ID=360mm that is 60 mm higher than conventional advised in the region. In the average demand years of past and current weather, Alternative 1 requires the same ID=270mm while a smaller ID=240mm is simulated with both alternatives 2 and 3 due to the fact that available soil water ASW is presently depleted to the optimum yield threshold OYT at harvest.