Irrigation scheduling for furrow-irrigated maize under climate uncertainties in the Thrace plain, Bulgaria

Climate change creates uncertainties for irrigation management. To cope with them, simulations were performed for the present and scenario-built weather conditions that include a pessimistic scenario of precipitation decrease in the next 25 years. In a former study, the irrigation scheduling simulation model ISAREG was calibrated for two maize varieties: the water stress-resistant hybrid Kn-2L-611 and the water stress-sensitive hybrid H708. Both are subjects of this study, which compares four irrigation scheduling alternatives: (1) refilling the soil reservoir and adopting a management-allowed depletion fraction (MAD) of 0.47; (2) refilling the soil reservoir and adopting MAD=0.33; (3) partially refilling the soil reservoir and adopting MAD=0.47; and (4) crop without irrigation. For the very dry year and the present climate all alternative irrigation schedules behave similarly but for the average year, alternatives 1 and 3, allowing a larger soil water depletion with MAD=0.47, require less water than the alternative with MAD=0.33. However, analysis of impact on yields using simulations relative to every year during 1970–1992 shows that alternative 2 leads to less impact on yields. The results of simulations were compared with irrigation schedules presently advised in the region and show that the latter do not fully cover crop requirements in dry seasons, when some yield decrease occurs. Simulations for the pessimistic scenario show that all three irrigation scheduling alternatives can easily accommodate the foreseen changes mainly by selecting suitable irrigation dates. The results of simulations do not allow selecting one among the three alternatives as the best irrigation scheduling strategy but are useful for later building an information system for farmers using actual weather data. Relative to the rainfed crop, the results indicate that yield impacts highly increase for the pessimistic scenario, particularly for the water stress-sensitive hybrid H708. The results indicate that vulnerability to climate change is higher for non-irrigated crops and that coping with possible rainfall decreases requires adopting less sensitive crop varieties, including when deficit irrigation would be applied for water saving.