The results of two year studies on the issue of the effects of sowing dates (early, optimum and late), pre-sowing seed treatment micronutrient fertilizers Rexolin and foliar application of soybean crops with micro fertilizers in chelate-based Rexolin and Brasitrel in the conditions of left Bank Forest-steppe of Ukraine on the work of the symbiotic apparatus in soybean plants have been submitted. The effects of these factors on the formation of seed yield of this crop have been discovered.

Interest in the cultivation of soybean in Ukraine is growing today; accordingly to this the area of its sowing is increasing. But the yield of this crop remains low. It has been determined by the imperfection of elements of technology of soybean cultivation. Therefore one of the priorities of agrarian science is to improve existing agro-technical methods of its cultivation.

Soya plants, entering into a symbiosis with module bacteria, are able to assimilate molecular nitrogen from the air transforming it into ammonium form and supply to the plants in exchange for products of photosynthesis. The presence of sufficient amount of micro fertilizers during the growth and development of soybean is required for effective nitrogen fixation is required. The use of which is of great importance in the metabolism of plants. In addition it is known that microelements are part of many biologically active substances, they affect enzymatic processes and improve the use nutrients and fertilizers by the plants.

Of great importance in the process of nodulation and nitrogen fixation are elements such as molybdenum and boron. To meet the needs of soybean plants above mentioned microelements by manufacturing chelated micronutrient fertilizers that contain nutrients in easily accessible and digestible form. They are used by pre-sowing seed treatment and foliar application at critical periods of growth and development of soybean plants: in the phases of budding and the formation of green beans and seed ripening.

The purpose and objectives of the study was to investigate the effect of pre-sowing treatment of seeds and foliar fertilizing with micro fertilizers for different sowing dates on the peculiarities of formation and functioning of the symbiotic apparatus in soybean plants and yield of its crops.

The research was carried out in 2013–2014 in the experimental field of Poltava state agricultural experimental station named after. M. I. Vavilov of the Institute of pig and APP NAAS of Ukraine.

The experimental setup involved the study of action and interaction of three factors: A – sowing date (early – at soil temperatures of 10 °C at a depth of 0–10 cm; the optimum is at a temperature of 12 °C at the depth of 0–10 cm; late – at soil temperatures of 14 °C at a depth of 0–10 cm); B – pre-sowing seed treatment micronutrient fertilizers (untreated; treatment by Rexolin); C – foliar application of micro fertilizers (without feeding; feeding by Rexolin; feeding by Brasitrel).

Soybeans have been sowed, guided by the temperature characteristics of the soil according to the scheme experience range type seeds of varieties of Romantika. Before sowing seeds were treated with micro-fertilizers Rexolin (150 g/ton of seeds). During the growing season was carried out foliar application with water soluble micro fertilizers in chelate-based Rexolin normal 500 g/ha and Brasitrel with the drug consumption of 3 l/hectares.

The results of two year studies indicate the influence of pre-sowing treatment of soybean seeds and foliar fertilizing of crops during the growing season with micro fertilizers in different sowing periods on the formation of the number and mass of nodules. Intensive growth of nodules occurred before the phase of ripening of the seeds. Counting their number showed that most nodules formed on soybean roots in the early period of sowing on the plots where they had a foliar feeding of crops with Rexolin and Brasitrel in combination with pre-sowing treatment with Rexolin – of 48.1 and 48.7 Ps/plant, respectively, an increase of 9.4–10.0 Ps/plant in comparison with the control.

A slightly less number of nodules formed at the plots of optimal and late sowing dates. So, in the ripening phase of the seeds at the optimum time of sowing there were on average one plant 36.4–46.6 Ps, late – 34.7–43.6 Ps. It can be explained by the negative influence of the external environment.

Foliar application with micro fertilizers without seed treatment had a lesser effect on the formation of nodules than the use of them in combination (pre-sowing treatment of seeds + fertilizer during the growing season).

It was also determined that depending on sowing time and application of micro fertilizers changes not only the number of nodules on the root system, but also their weight. Maximum results were recorded in the ripening phase of the seeds. Depending on options of experience weight of nodules ranged 457– 692 mg/plant at the first sowing time, 419–640 mg/plant for the second and 401–595 mg/plant for the third time of sowing.

The results indicate a significant influence of the studied factors on the yield of soybean. On average over two years of research it varied in the range of 1.52 to    2.48 t/ha depending on hydrothermal conditions of year, sowing dates and use of micro fertilizers.

Thus, in conditions of left Bank Forest-steppe of Ukraine studied elements of technology (pre-sowing treatment of soybean seeds and foliar nutrition of crops during the growing season micro fertilizers in chelated basis for different sowing dates) have a positive effect on the development of nodule bacteria, symbiotic activity and grain yield of soybean crops. In embodiments where the observed maximum values of total number of nodules (of 48.1 and 48.7 Ps/plant) and their weight (681 and at 692 mg/plant), and formed the highest yield of soybean seeds is between 2.39 and 2.48 t/ha.

Key words: soybean, seeding time, Rexolin, Brasitrel, the total number of nodules, weight of nodules, yield.