Photosynthetic activity of sunflower hybrids under growth regulators in the Steppe of Ukraine

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