Creation of optimal conditions for growth and development of maize is the basis for increasement the crop produtivity. One of the key elements in the technology of corn growing is a proper selection of hybrids concerning soil-climatic zones and the determination of the optimum sowing terms.

Optimization of maize sowing was given a lot of attention, but mostly all researchers focused on hybrids of grain-growing direction, at the same time it is practically not studied the question of growing this crop for silage production. With appearance of new maize hybrids with different maturity and morphological structure, biological characteristics and properties, there is a need to further improvement and development of optimal conditions of high quality technology, in particular the sowing dates.

The purpose of thivs study is to determine the optimum sowing terms of maize hybrids of different maturity groups that increase the productivity and nutritive value of silage materials.

Field experiments were conducted during 2011-2013 in the experimental field of BNAU, located in the Central forest-steppe zone of Ukraine.

In the scheme of the experiment it were included hybrids of different maturity groups of the Institute of agriculture in the steppe zone of NAAS of Ukraine: the early-maturing Tovtryanskiy 188 SV, middle-early Bilozirskiy 295 SV, middle-maturing Monica 350 MV and medium Bystriza 400 MV, which were sown in three terms: the first – when the soil temperature at seeding depth was 6-8°C, the second – 8-10°C (control), the third – 10-12°C.

Weather conditions of vegetation period of maize in 2011-2013 years were favorable for moisture and temperature. In 2012 under the influence of high temperature and water deficit it was observed the soil and air drought that adversely affected the productivity of studied hybrids.

According to our research during the first term, the period from sowing to the appearance of significantly lengthened shoots was caused by the temperature conditions of soil during seed germination and biological properties of the investigated forms.

On average, over a three-year period from sowing to germination during the first term of sowing was 16-19 days, the second 14-16 days, the third – 11-12 days. In the variant with corn planting when the soil temperature was 10-12 ° C, the vegetation period in all studied hybrids was short: in Tovtryanskiy 188 SV – 97 days, Bilozirskiy 295 SV – 102 days, Monica 350 MV – 105 days, Bystriza 400 MV – 112 days. Vegetation period of hybrids has grown with the increased FAO indicators.

The maximum area of leaf surface per plant was formed in the flowering phase of panicles and depending on the hybrid it ranged 34,7-50,1 thousand m²/ha. The indicators were high during the second and third planting dates, and advantage of this indicator among hybrids was on medium hybrid Bystriza 400 MV (48,2-50,1 thousand м²/ha).

In the phase of milky-wax ripeness the leaf surface of studied hybrids decreased in comparison with the phase of flowering panicles in hybrid Tovtryanskiy 188 SV 7,1-8,1%, Bilozirskiy 295 SV - 5,0-5,8%, Monica 350 MV – 6,0-6,9% and Bystriza 400 MV - 4,7-6,3%.

Our research found out that the growth of vegetative mass in corn hybrids ended in the milk phase of grain, the accumulation of dry matter continued until wax ripeness and it was due to nutrient movement from the vegetative organs to the reproductive ones.

The highest dry matter content of maize plants during all phases of growth and development was in the variant of sowing when the soil temperature at seeding depth 8-10 °C, at 0.2-1.4 % more than other options.

On average during three years, the highest yield of green mass of the studied hybrids observed in the variation of sowing at the soil temperature 10-12 °C: the hybrid Tovtryanskiy 188 SV – 43.6 t/ha, Bilozirskiy 295 SV – 46.0 t/ha, Monica 350 MV – 49.8 t/ha, Bystriza 400 MV – 51.0 t/ha. But mid-early, middle and medium late hybrids difference between the second and third sowing was negligible and in adverse conditions higher yields are provided by crops sown at the soil temperature 8-10°C.

Among the given hybrids, the maximum productivity was characterized by medium Bystriza 400 MV – 46,2-51,0 t/ha.

Key words: corn, hybrids, sowing terms, productivity, green mass, interphase periods, leaf surface area, dry matter.