Effect of the main soil tillage systems on the productivity and yield structural elements of sunflower (Helianthus annuus L.) - hybrid Deveda

Sunflower yield (Heliantus annuus L. - hybrid Deveda), obtained under different main soil tillage systems in 4-field crop rotation (common bean-wheat-sunflower-grain maize), is strongly influenced by the regional soil (Haplic Chernozems) and the climatic conditions. This study was carried out at the stationary field trial of Dobrudzha Agricultural Institute-General Toshevo, from 2016 to 2021. The influence of seven main soil tillage systems (MSTS) on the yield, and its components and the physical properties of sunflower seeds were investigated. Four of these MSTS were applied independently and annually in crop rotation: 1. CP - conventional plowing (24-26 cm); 2. D - disking (10-12 cm) 3. C - cutting (chisel-plough); 4. NT - nil tillage (direct sowing). The other three MSTS systems included: 5. Conventional plowing (for spring crops) - Nil tillage (for wheat); 6. Cutting (for spring crops) - Disking (for wheat) and 7. Conventional plowing (for spring crops) - Disking (for wheat). The mineral fer-tilization in the crop rotation was as follows: Common bean - N60P60K60; Wheat - N120P120K60; Sunflower - N60P120K120 and Maize - N120P60K60. The objectives were: (i) to investigate the seasonal variability in sunflower yield - hybrid Deveda and its structural elements as influenced by the tillage systems; (ii) to investigate the variability in the physical properties of sunflower seeds and (iii) to evaluate the correlations between the yield and all investigated indices.A significant differentiation was determined in the productivity of sunflower depending on the tested systems for main soil tillage by years and average for the period 2016-2021. The highest average yields were obtained in 2017, followed by 2019. The most unfa-vorable for the development, productivity and physical qualities of the seeds are in 2020, characterized by extreme drought in the crit-ical phase of crop development. Drought causes a decline in yield compared to the year with the most favorable conditions by 39%. Among the annual independently applied systems, constant Nil-tillage and constant Disking were most unsuitable for ex-pression of the production potential of the hybrid "Deveda". The mean yield reduction according to the constant Conventional plowing (4522.9 kg/ha) in the crop rotation were 836.9 kg/ha and 654.0 kg/ha, respectively.The systems involving annual alternation of tilths with turning of the plow layer give way the independently applied conven-tional one with average 285.2 kg/ha (6.74%). From an agronomic point of view, most efficient for sunflower in Sough Dobrudzha region was the constant conventional plowing, or alternation of plowing prior to spring crops and direct sowing of wheat. The test-ed tillage systems have a significant impact on the morphological and yield-related traits of sunflower by years of investigating.The values of the seed's physical properties were also considerably differentiated depending on meteorological condition and the kind of main soil tillages. The constant use of Nil-tillage in the crop leads to the production of the largest seeds- 1000 kernel weight 50.35 g. The heaviest seeds were obtained in 2019. It is obvious that the constant application of deep irreversible tillage leads to the production of seeds with the highest values of test weight.The strongest connection is the yield with the formed reproductive organ (0.797 **), followed by that with the total formed aboveground biomass (0.685 **).