Leaf Area Formation and Photosynthetic Activity of Sunflower Plants Depending on Fertilizers and Growth Regulators

The study presents scientific substantiation and determination of the dependence of leaf area formation and photosynthetic activity of sunflower plants under the influence of fertilizers and growth regulators. The field research was conducted in 2015-2017 in the fields of the Voznesensk district in the Mykolaiv region, Ukraine (GPS: 47.630518, 32.078974). The soil of the research field is common black soil with little humus accumulation and the content of hydrolyzed nitrogen – 1.5-1.8; the content of highly absorbable phosphorous – 4.5-7.0 and the content of exchangeable potassium – 12-15 mg/100 g of soil. The research was carried out by a two-factor scheme, where Factor A – the rate of mineral nutrition (the test plot without fertilizers; N30P45; N60P90); and Factor В – foliar feeding with the Wuxal Microplant, Khelafit Combi and Fitomare preparations. The weather conditions in the years of the research were typical for this growing zone. It was established that the year 2017 was the least favorable with excessively low soil moisture and high temperature regime for growing the crop, and the weather conditions of 2015 and 2016 were the most favorable for cultivating sunflower. The research made it possible to determine that fertilizers combined with multifunctional preparations had a considerable impact on the leaf area and photosynthetic potential of agrocenosis. It proves that foliar feeding of sunflower plants at the stage of 6-8 true leaves with growth regulators contributed not only to a change in the total chlorophyll content, but also to its fractional composition. In all the cases there was a major increase in the content of the fraction "а". In particular, the maximal increase in this fraction was 90%, whereas the difference did not exceed 76% in the fraction "b". Under nonfertilized conditions these indices were 48 and 13%, respectively.