Productivity of corn as affected by the accumulation of heat units and different nitrogen fertilizers

Purpose. To establish the effectiveness of the application of different fertilizers in corn cultivation technologies in the Left Bank Forest Steppe of Ukraine, depending on the weather conditions of the years of research. 
Methods. Field research was conducted in the years 2019–2021 in dark grey podzolized soil. The results of the study were calculated using the SAS 9.4 software package. Analysis of variance was performed using the Duncan rank criterion. 
Results. Calculations of the accumulation of heat units showed a significant difference by year, which largely determined the level of corn productivity. During vegetation, the sum of active temperatures in the conditions of the northern regions of the Left Bank Forest Steppe varied, on average for 2019–2021, from 3235 (May–September) to 3731 (April–November). The largest range of difference between the sums of heat units was for the period April–October, from 3550 in 2019 to 3845 in 2021, which indicates the potential for earlier corn sowing dates in this region under favorable weather conditions. Corn hybrids ‘EU Concord’ and 'EU Asteroid' are quite plastic and respond positively to optimization of nutrition. Application of N22Р57К57 in the form of diamophoska provides an increase in the yield of their grain by 0.99–1.01 t/ha, or 16.3–16.4%. Additional application of nitrogen fertilizers against the background of diammonium phosphate provides an increase in yield from 0.57 to 1.33 t/ha, or by 8.0–18.6%. With the introduction of potassium ammonium nitrate (KAN 32), the yield increase in ‘EU Concord’ was 2.19 t/ha and in ‘EU Asteroid’ 2.34 t/ha compared to the control. 
Conclusions. The sum of the accumulated heat units during vegetation more objectively characterizes the thermal resources of the area compared to the sums of positive, active and effective temperatures, which makes it possible to more accurately determine the optimal dates for sowing and the end of the crop vegetation season in the conditions of the research region. Applying nitrogen in several ways optimizes the nutrition of corn plants, ensuring an increase in individual productivity and grain yield up to 18.6%.