Analysis of meteorological factors shows that the temperature sums during the vegetation of the main crops grow but are relatively stable, ie. they are not a limiting factor for their normal growth and development. Rainfall, however, in terms of quantity and distribution changes in a considerably wider range over ten days periods, months and years. The instability of this meteorological factor predetermines irrigation as a major event of the agro-technical complex, which is decisive for the achievement of high and sustainable yields.
Increasing water deficit requires the use of water-saving irrigation technologies in the practice of irrigated agriculture and the conduct of research to optimize irrigation regimes in order to increase the efficiency of irrigation water used. One of the ways to achieve this goal is irrigation with reduced irrigation norms while preserving the number of waterings. The advantage of these reduced irrigation regimes is the saving of water at acceptable yield losses. Their application is warranted when there is a possibility of accurate dosing of irrigation water and the irrigations are of low cost.
In order to establish the irrigation regime of apples in drip irrigation, field experiments were carried out on the Chelopechene-Sofia experimental field. Irrigation is carried out with a drop in pre-watering humidity to 85% of WHC and variants irrigated by a reduction of irrigation rate with 20% and 40% compared to the variant irrigated at 100% WHC and non-irrigated variant.
The conducted irrigated regimes during the years have had an impact on the yields obtained, with the highest results being obtained for the irrigated variants with 100% irrigation rate and the lowest for the non-irrigated variants. The largest increase in yield was obtained in 2004 (characterized as dry), which is with 55% (apples) more than non-irrigated variants, and the smallest increase of 25% (apples) was obtained during the humid 2005.