Irrigation scheduling under climate uncertainties in North-West Bulgaria

Abstract

The objective of the present study is to develop alternatives of precise irrigation scheduling for maize crop grown on a Degraded Chernozem soil in Gorni Dabnik experimental field and to define the impact of climate variability and change on irrigation management and yield relative to late and semi-early maize hybrids there over the period 1951-2004. The validated simulation model of water balance, irrigation scheduling and yield impacts of water stress WINISAREG is applied. The studied irrigation options are: (1) refilling soil reservoir to field capacity FC by adopting a management allowed depletion fraction MAD=0.47, i.e. up to 79% of FC, and 90 mm application depths; (2) refilling soil reservoir to FC by adopting a depletion threshold MAD=0.31, i.e. pre-irrigation soil moisture 86% FC, and 60mm application depth; (3) aims at better storage and use of precipitation and irrigation water and consists of partial refilling the soil reservoir to 84% TAW by adopting MAD=0.47 and 60mm application depth. It has been found that: (1) Net irrigation requirements NIR vary from 0-10mm in extremely wet to 80-170 mm in the average, reaching 260 mm in the very dry 1963 of the past 1951-1984 period; (2) Schedule 2 leads to higher irrigation demands (ID) when compared with schedules 1 and 3, under which seasonal precipitation and soil water storage are more efficiently used and irrigation depths (ID) are 30 to 90 mm lower; (3) Relative to present weather condition, drought mitigation measures consists of application of environmentally oriented water saving schedules 1 and 3 with precise irrigation timing; (4) Considering the semi-early maize hybrids, as Pioneer 37-37 and Kneja-2L-611, yield impacts of water stress is mitigated. Yield losses relative to rainfed maize are 15-30% in the average year, while in the very dry year they do not surpass 60% of the potential yield.