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The investigation was carried out during 2014–2016 in the land of General Toshevo, the South Dobrudzha region of Bulgaria on slightly leached chernozem soil type. The effect of the types of soil tillage for sunflower given bellow was followed: ploughing at 24–26 cm, chisel-plough at 24–26 cm, disking with disk harrow at 10–20 cm and direct sowing (no-tillage) on the bulk density, the moisture content and the temperature of soil. The additional soil tilths of the areas subjected to ploughing, chisel-ploughing and disking with disc harrow included double spring pre-sowing cultivation with harrowing. To destroy the emerging weeds in the variant with direct sowing, a total herbicide was applied. The investigated physical parameters of soil were followed during three main stages of sunflower development: emergence, flowering and technical maturity. The bulk density of soil was determined by soil samples taken from the 0–10, 10–20 and 20–30 cm layers. The soil temperature was read at 800, 1200 and 1600 h to depth 2, 5, 10, 15, 20 and 25 cm with classical soil thermometer. For evaluation of the results dispersion and regression analyses were used. In the slightly leached chernozem soil type, the conventional ploughing leads to lower bulk density in the cultivated soil profile. Under minimal tillage, slight increase of bulk density of the layer underlying the cultivated one was observed over time. The bulk density under tillage without turning of the soil layer and no-tillage was changed and formed primarily under the influence of physical and climatic factors, and under minimal tillage – under the cultivated layer. Under all investigated types of soil tillage, bulk density increased down the soil profile. Replacing ploughing with tillage without turning of the soil layer, minimal and no-tillage lead to decrease of soil temperature. The most significant differences were observed in the 0–10 layer, which, on its part, conditioned accumulation and transfer of thermal energy along the soil profile. The soil temperature decreased with the reduction of the number and depth of the soil tillage operations. The temperature amplitudes between the surface layer and the underlying soil horizons in the areas with ploughing, chisel ploughing minimal and no-tillage were lower. The results concerning the values of the investigated physical properties of soil under different types of soil tillage were statistically significant at different levels of P.

The investigation was carried out at the Dobrudzha Agricultural Institute – General Toshevo during 2010-2011. The effect of some fertilization products for leaf application (Amalgerol Premium, Foliar Extra, Hi-Phos, Bo-La and КТС) on the development and productivity of the San Luka and Yana sunflower hybrids was studied. Two check variants were used: one without fertilization and one with application of N60P120K80. San Luka and Yana were sown at a density 55 000 plants/ha. At budding stage the San Luka and Yana plants had the greatest plant height in the variants fertilized with N60P120K80 and treated with the leaf application products Foliar Extra and Hi-Phos. The highest seed yield from both hybrids during the years of investigation was obtained from the variant with conventional treatment followed by the variants treated with Foliar Extra, Hi-Phos, КТС, Bo-La and Amalgerol Premium. The head diameter in all variants treated with leaf fertilizers in both investigated hybrids was smaller than the diameter of the heads from the check variant treated with N60P120K80. Among the fertilizers for leaf application, Foliar Extra had the highest effect on the head diameter, followed by Hi-Phos. In comparison to the check treated with N60P120K80, there was no significant increase of the seed weight per head in any of the variants with leaf treatment.