Water regime and drought tolerance of apple trees at foliage spraying application

The influence of foliage spraying on water regime indications (leaf water content, ratio of bound and free water, water deficiency) has been studied in the field experiment with "Imrus" apple tree on intercalary stock 3-4-98. These indices make it possible to establish apple tree response to stress factors of summer period. The experiment was conducted in edaphoclimatic conditions of the Central Russian Upland (Orel region) in 2014-2015. The following spray treatments were performed: 1.Control (water treatment); 2.H3BO3 - 0.1%; 3.K2SO4 - 0.3%; 4.CaCl2 - 1%; 5.H3BO3+K2SO4; 6.H3BO3+CaCl2; 7.K2SO4+CaCl2; 8. H3BO3+K2SO4+CaCl2. The treatments were done five times during the vegetation period. A significant influence of foliage spraying on water regime indications was revealed. This influence depended on meteorological conditions and yield load and was more visible in 2014 (high yield, drought). In August 2014 (the hottest month) all treatments (except spraying of К2SО4) resulted in total water content reduction in apple leaves (1.8-3.0% fw compared with control). Foliage spraying of CaCl2 led to the least total water content (51.25% fw) and the greatest ratio of bound water to free water (13.7) during this month. Spraying of Н3ВО3,К2SО4, К2SО4+СаСl2 and Н3ВО3+К2SО4+СаСl2 increases water deficiency of apple trees (2.6-4.0% fw compared with control). In unfavorable meteorological conditions the treatments with К2SО4 contributed to the increase of tree productivity. At the same time the treatments with CaCl2 had a contrary effect on the yield because of the lowering of physiological process intensity.