FORMATION OF THE ASSIMILATING SURFACE BY SUNFLOWER HYBRIDS UNDER THE INFLUENCE OF NUTRITIONAL CONDITIONS AND RETARDANTS
Authors: Harbar L. A. , Avramchuk V. I. 
Published: October 2023

Crop productivity management includes parameters that characterize the activity of the assimilating plant surface and ensure the formation of dry matter. The characteristic of agrocenosis plants includes not only the value of the leaf surface area, but also the parameters of the distribution of leaves on the plant, their number and layering. Attention is also paid to the study of the distribution of assimilants synthesized in the leaf mass of different leaf tiers to other vegetative and generative organs of the plant. These factors entail a problem associated with a decrease in the level of provision of sunflower plants with an assimilating surface. It can be solved by selection to increase the shade tolerance of the lower tier of leaves of new varieties and hybrids of the crop and by optimizing individual elements of the cultivation technology. In particular, the improvement of nutritional conditions and the use of growth regulators. The use of retardants can ensure the formation of a powerful assimilating apparatus that determines the productivity of a crop. This is explained by the ability of the latter to influence the morphogenesis of the plant, and, accordingly, the intensity of the photosynthesis process, the redistribution of the synthesized substances, nutrients, providing an increase in yield, oil yield and its quality. The purpose of the research was to identify the influence of nutritional conditions, retardant on the activity of the assimilating surface of sunflower hybrids in the conditions of the Right-Bank Forest-Steppe of Ukraine. The studies were carried out in a separate division of the National University of Life and Environmental Sciences of Ukraine "Agronomic Research Station" on typical low-humus chernozems with a humus content of 4.32%. Soil supply with nitrogen is low, potassium and phosphorus - medium. Experience is threefold. Factor A – sunflower hybrids (RGT Wollf, Alzan, ES Bella, Lime); factor B - fertilizer (calculation of planned yields by the balance method); factor C - application of the Setar retardant (ВВСН 30-32, 0.5 l/ha). Fertilizers were applied according to the scheme of the experiment: nitrogen – for pre-sowing cultivation, phosphorus and potasium at primary tillage. The determination of the leaf surface area was carried out by scanning, followed by the calculation of plant density per ha. The photosynthetic potential was determined by the calculation method. The results of the conducted research during 2021-2022 shave shown that with the growth and development of plants, a gradual increase in the area of sunflower plant leaves of all hybrids studied was observed. The parameters of the leaf surface changed at all stages of plant development, depending on the genetic characteristics of the hybrid and the nutritional conditions that were created by the fertilizer options. Microstages 64-68 were characterized by the maximum indicators of the assimilating surface of sunflower plants, which varied in the range of 39.3-47.9 thousand m2/ha. Subsequently, there was a decrease in the leaf surface of plants as a result of the death of the lower leaf blades. The area of leaves, depending on the variant of the experiment, at 74-78 microstages of development decreased by 6.3-10.2 thousand m2/ha. The indicators in the context of variants varied from 32.8–37.7 thousand m2/ha. The highest results were obtained on the variant with the introduction of N120P80K180. This relationship was observed in all hybrids that we studied. When using the Setar retardant (0.5 l/ha) on sunflower, there was a tendency to increase the leaf area by 1.5–6.8 % compared to the variants without treatment. The maximum indicators of leaf surface area when comparing hybrids were obtained for all variants of fertilizer and at all stages of development of sunflower plants of the RGT Wollf hybrid. The calculation of the photosynthetic potential at certain stages of development of sunflower plants showed an increase in indicators with an increase in fertilizer application rates. In the period 34-58 microstages of development, the photosynthetic potential changed depending on the variant of the experiment from 1.058 to 1.358 million m2/ha day. Indicators of the photosynthetic potential of crops decreased and varied from 1.188 to 1.292 million m2/ha day at BBCH 58-68. The use of the retatardant Setar provided an increase in performance compared with the options without one. Maximum leaf area were obtained on the variants of the hybrid RGT Wolf. Correlation analysis between indicators of leaf area and sunflower yield indicates a direct positive correlation with correlation coefficients in the context of hybrids 0.977-0.987.