Conducting sustainable agriculture involves not only increasing the productivity of crops and increasing the volume of crop production, but also preserving ecosystems. Mulching the soil in orchards is one of the ways to preserve the natural balance of agricultural landscapes. But the effect of competition with grasses on the biochemical composition of fruit tree tissues has not yet been definitively elucidated. The purpose of this study was to determine the influence of soil retention under mulching (compared to pure steam) on the biochemical composition of cherry leaf tissues. The research was conducted in an organic cherry orchard (Prunus avium L. / Prunus mahaleb) during 2017-2019 in the conditions of the Southern Steppe of Ukraine. A significant decrease in the content of ascorbate, glutathione, sugars, total reducing activity and activity of antioxidant enzymes was established under conditions of prolonged drought and an increase in the content of titrated acids. The total reducing activity under mulching conditions tended to increase. A gradual increase in the content of titrated acids, ascorbate, sugars, phenolic substances, and glutathione was recorded in the leaves of cherry trees from the flowering phase to November. In the autumn phase, a significant increase in sugars and phenolic substances was established in cherry leaves under the conditions of mulching in 2017, and in 2018 – phenolic substances; in 2019 – phenolic substances and ascorbate. An increase in the content of malondialdehyde (MDA) and the activity of antioxidant enzymes was found during the growing season of cherries in both variants of the experiment. In the November phase only in 2019, the MDA content was significantly higher by 14% under the condition of mulching. Under mulching conditions, a significant increase in ascorbate peroxidase (by 28-30%) and polyphenol oxidase (by 45-46%) was determined. In 2018 and 2019, a 2.4-fold increase in peroxidase activity in cherry leaves was determined. Research results help to understand the mechanisms of adaptation of fruit plants to stress factors (drought, competition with natural grasses) and can be used as an argument in favour of mulching in organic cherry orchards.

The climate of the southern steppe zone of Ukraine in recent years has been characterized by substantial warming, with a low, uneven amount of precipitation during the growing season of plants, which leads to a decrease in the reserves of productive moisture in the soil, and hydrothermal stress occurs in plants. Opportunities to increase the adaptation of plants to adverse factors are the use of plant growth regulators and the use of various methods of tillage aimed at preserving moisture. The purpose of this study was to investigate the influence of the plant growth regulator AKM+Ca on the operation of the photosynthetic apparatus of sunflower hybrids against the background of various methods of basic tillage in the conditions of the Southern Steppe of Ukraine. The following methods were used during the study: field, chemical (to determine qualitative indicators), and statistical (to assess the reliability of data). Field studies were conducted during 2017-2019 on southern heavy loamy chernozems. In the experiment, modified plant growth regulator AKM+Са was used for pre-sowing seed treatment and foliar spraying of sunflower plants (beginning budding phase) of Talento and Colombi hybrids against the background of deep loosening or ploughing. It was found that the use of deep loosening, in contrast to ploughing, helps increase the dry matter content in sunflower plants and the net productivity of photosynthesis due to better preservation of moisture in the soil. The use of plant growth regulator AKM+Са, regardless of the method of soil cultivation, contributes to the increase in the leaf surface area up to 31.2%, increases the photosynthetic potential of plants to 21.6% and the net productivity of photosynthesis to 15.9% during the growing season, and also increases the content of dry matter, compared to the control. The proportion of influence of the plant growth regulator AKM+Ca on the formation of the leaf surface area is 54.2%. The maximum positive effect was obtained with the combined use of AKM+Ca for pre-sowing treatment and spraying of sunflower plants during the growing season against the background of deep loosening of the soil. The research results can be used to adjust elements of agricultural technologies for growing sunflower seeds, increase crop productivity and conduct profitable agribusiness