The determination of the assimilative surface in diverse maturing maize hybrids showed the differences in their growing in the different phases of growth and development.

The maize leaf surface reached its maximum value in the milk ripeness phase, and further the accelerated aging and dying off of lower leaves was observed particularly in early maturing hybrids.

With maize leaf surface growing the FAS utilization increased, which at the beginning of vegetation in the phase of 6-8 leaves was low and gradually increased up to the end of ear emergence phase. Plant density of diverse maturing hybrids had A significant impact on FAS utilization. The plant density increase of from 80,000 to 100,000 plants/ha raised the FAS utilization factor by 11-31 %. Further maize thickening (from 100,000 to 120,000 plants/ha) tended to reduce the FAS utilization by 5-10 %.

The photosynthetic potential of maize crops increases during the growing season and reaches its maximum in the milk ripeness phase in mid-maturing hybrid at the plant density of 100,000 plants/ha.

The FAS utilization intensity of maize, its maximum photosynthetic potential in case of plant thickening contributes to energy accumulation in dry matter and increases the yield rate.

The indexes of the net photosynthetic productivity, which change throughout the plant growth, are used to measure dry matter accumulation by unit of maize leaf surface area. The maximum value of maize net photosynthetic productivity was observed during the ear emergence phase when the largest assimilation surface was recorded.

There is a direct correlation between the net photosynthetic productivity and dry matter accumulation. It has been established that the highest biomass accumulation of diverse maturing maize hybrids was in the interphase period between ear emergence and milk ripeness phases. The net photosynthetic productivity in milk-wax ripeness phase decreases due to the leaf area decrease compared to milk ripeness phase.

In the early growing season of maize (phase of 6-8 leaves) the highest dry matter yield was recorded in early maturing hybrid at the density of 80,000 plants/ha. The dry matter yield in medium early and mid-maturing hybrids is bigger than in early maturing hybrids during the milk ripeness phase. It should be noted that the maximum yield of dry matter has been accumulated in mid-maturing maize hybrids at the plant density of 100,000 plants/ha in the milk ripeness phase.

Thus, the dynamics of photosynthetic intensity of mid-maturing maize hybrids shows their advantage over early maturing hybrids in daily carbon dioxide absorption, which ultimately contributes to higher yield formation.

The growing techniques influenced the rates of maize hybrid photosynthetic productivity. Plant density increase of from 80,000 to 100,000 plants/ha enlarged the leaf surface area by 5-10 %.

The highest dry matter yield was observed in mid-maturing maize hybrids at the plant density of 100,000 plants/ha in the milk ripeness phase.

Key words: maize hybrids, photosynthetic productivity, plant density, dry matter yield.