This article presents the results of the studies carried out in the Central Forest-steppe area of Ukraine. The research focused on the impact of stand density of corn hybrids of different maturity groups on the photosynthetic plant activity, dry matter accumulation and green mass yield.

Introduction of new corn hybrids and their cultivation methods into production, identifying their optimal crop stand density will increase and stabilize maize yields, strengthen the Ukraine’s fodder and food balance. The problem of establishing differentiated density for the new hybrids in certain soil and climatic conditions has been a very important issue which crop production has been facing recently.

Corn hybrids with different maturity degree do not equally response to the change in plant stand density under unstable conditions, and in some years due to low humidity as well. Therefore, the performance of the hybrids of different maturity groups can be identified correctly only in case of differentiated plant stand density for each hybrid according to the agro-environmental conditions of its growth.

Under favorable conditions, corn assimilation system is able to absorb the maximum amount of solar radiation which positively influences moisture and nutrition absorption level as well as the accumulation of the significant amount of the organic substances.

In the course of the research trial, the total area of the crop leaf surface per hectare increased due to its density, and reached its maximum when the highest plant stand density was achieved. The plant stand density significantly affected the leaf surface growth dynamics.

At the initial stages of their development, the early-maturing corn hybrids exceeded the middle- and middle-late maturing hybrids in their total leaf surface, although in the later vegetation periods the last two hybrids showed a significant advantage.

The maximum leaf surface area was marked at the panicles flowering stage with the density amount of 120,000 plants/ha which comprised 47.0, 49.6, 51.3 and 55.2 thousand m²/ha, respectively in hybrids DP Pyvyha, DP Galatea, Monica 350 MV and Bystrytsia 400 MV, which exceeded the control variant (90,000 plants/ha) in 6.3, 5.7, 5.8 and 6.1 thousand m²/ha.

The improved spatial plant allocation of plants ensured by sowing stand density stand at the level of 90,000 plants/ha, makes it possible to increase the rate of the net photosynthesis productivity in maize hybrids during the whole vegetation development of plants.

Obviously, it is linked to the improved use of soil moisture plant absorption and more efficient use of nutrients and solar radiation, especially in the second part of the vegetation development.

The dry matter content indicators in the corn hybrids increased as the crop density level rose. The increase in the quantity of the early- and middle-early maturing hybrids from 90,000 to 120,000 plants/ha resulted in the growth of this index in the wax ripeness phase in 0.6 % and 0.4 % and in the middle- and middle-late maturing in 0.5 % and 0.7 % respectively. The highest dry matter content in maize hybrids was observed in the grain wax ripeness phase. It should be noted that the dry matter accumulation in maize hybrids continued up to the wax ripeness phase.

The hybrid Bystrytsia 400 MV in all the periods of observation was marked by the highest dry matter content (28.4-29.1 % and 31.8-32.5 %).

The highest dry matter accumulation rate was observed during the phase of wax ripeness in the early-maturing hybrids DP Pyvyha and DP middle-early Galatea for the density versions of 110,000 and 120,000 plants/ha which comprised 13.5 and 13.7 tons/ha, 15.0 and 14.8 tons/ha; in the middle-maturing hybrid Monica 350 MV and middle-late maturing Bystrytsia 400 MV with density of 90,000 and 100,000   plants/ha – 15.9 and 16.2 tons/ha, 16.9 and 17.0 tons/ha respectively.

The green mass yield in the corn hybrids varied under the influence of the biological features of forms, the plant stand density rates and the prevailing weather conditions during the year when the trial was conducted.

On average during four-year research trial, the maximum green mass productivity in the hybrid DP Pyvyha was formed at the density rate of 120,000 plants/ha and comprised 47.3 tons/ha, exceeding the control figure in 4.1 tons/ha. At the density rate of 110,000 plants/ha the yield rate reduced in 0.8 tons/ha. The hybrid   DP Galatea had the highest green mass yield rate at the density of 110,000 plants/ha (50.5 tons/ha), although the difference between 110 and 120,000 plants/ha during the trial years was insignificant.

The middle-maturing hybrid Monica 350 MV had the highest average green mass yield at the density 100,000 plants/ha – 51.9 tons/ha, increasing crop thickening  to 110,000 and 120,000 plants/ha led to the decrease in productivity in 5.1 and
8.5 tons/ha. The middle-late hybrid Bystrytsia 400 MV provided the maximum green mass yield in the trial which comprised 53.1 tons/ha in the control variant (90,000 plants/ha). A further increase in stand density led to the decrease in the green mass yield.

Key words: corn silage, productivity, dry matter, plant stand density, green mass, harvesting, hybrid.