The dissertation presents theoretical justification and results of three-year field experiments (2023–2025) aimed at determining the optimal seeding rates for the maize hybrid DKS 3939 (FAO 320) depending on field productivity zones in the northern part of Left-Bank Ukraine. The influence of seeding rate and productivity zone on actual plant stand density, duration of inter-phase and growing periods, biometric and structural-morphological traits, grain yield and quality, and by-product quality was established. An economic and bioenergetic assessment of the differentiated seeding rate technology was conducted, and zone-specific production recommendations were developed.
The study area was found to exhibit pronounced agro-landscape heterogeneity with spatial alternation of sod-podzolic soils, grey forest soils, and podzolized chernozems within a single field. Significant differentiation of agrochemical properties was recorded between productivity zones: soil pH ranged from 4.93 in the low productivity zone to 6.30 in the high productivity zone, humus content from 1.0 to 2.3 %, and cation exchange capacity from 5.03 to 11.07 cmol/kg. Soil penetration resistance at 30–35 cm depth in the low productivity zone was approximately 1.7 times higher than in the high productivity zone. Hydrothermal conditions varied substantially between seasons: the hydrothermal coefficient during the growing period was 1.05 in 2023, 0.55 in the drought year of 2024, and 0.96 in 2025, providing a wide range of agroclimatic scenarios for technology evaluation.
Actual plant stand density at harvest systematically differed between productivity zones regardless of seeding rate. Mean relative deviation from the planned seeding rate was 2.8 % in the high productivity zone, 3.6 % in the medium productivity zone, and 5.8 % in the low productivity zone. Growing season duration was primarily determined by productivity zone: the difference between high and low productivity zones reached 18.5 days from emergence to dough stage, while between extreme seeding rates it was only 6.5 days. In the low productivity zone, acceleration of vegetative phases and reduction of the grain filling period by an average of 9.2 days compared to the high productivity zone were observed, reflecting an adaptive drought escape response. Increasing seeding rate from 65 to 85 thousand seeds/ha extended the anthesis-silking interval from 9.2 to 13.4 days.
Plant height at silking showed a parabolic relationship with seeding rate, with a maximum at 80 thousand seeds/ha, but the influence of productivity zone was significantly stronger: the difference between zones was 59.1 cm compared to 12.9 cm between extreme seeding rates. Yield structure indicators – 1,000-grain weight, number of kernels per ear, test weight – showed pronounced differentiation between zones: the difference in 1,000-grain weight reached 45.8 g (15.7 %), and in kernel number per ear between extreme zone-rate combinations – 237 kernels (52.9 %).
Mean grain yield over the study years was 10.70 t/ha in the high productivity zone, 9.21 t/ha in the medium productivity zone, and 7.42 t/ha in the low productivity zone. Polynomial regression analysis established zone-specific optimal seeding rates: 81.8 thousand seeds/ha for the high productivity zone (projected yield 11.21 t/ha), 75.9 thousand seeds/ha for the medium productivity zone (9.56 t/ha), and 68.1 thousand seeds/ha for the low productivity zone (7.70 t/ha). Coefficients of determination exceeded 0.90 in most variants. Grain quality indicators showed consistent zonal differentiation: starch content increased from the low to the high productivity zone (68.9–70.8–72.1 %), while protein and fat content showed the opposite trend.
Economic efficiency of differentiated seeding was confirmed for all three zones. The highest profit in the high productivity zone was achieved at 80 thousand seeds/ha – 44,925 UAH/ha (+14.8 % compared to the control), in the medium productivity zone – at 75 thousand seeds/ha (35,219 UAH/ha), and in the low productivity zone – at 70 thousand seeds/ha (26,849 UAH/ha, +6.6 % compared to the control). The highest energy efficiency coefficient was recorded in the high productivity zone at 80 thousand seeds/ha – EEC=8.39. In the medium productivity zone the maximum EEC was 7.04 at 75 thousand seeds/ha, and in the low productivity zone – 5.69 at 70 thousand seeds/ha. The radiation use efficiency coefficient reached its maximum in the high productivity zone at 80 thousand seeds/ha – 2.37 %. The coincidence of economic and bioenergetic optima for all productivity zones confirms the structural stability of the recommended solutions regardless of grain market conditions.
