In the context of decarbonisation of both global agriculture and agricultural production in Ukraine, optimisation of nitrogen nutrition of maize is an extremely important and urgent issue, especially in the context of global climate change, which is also reflected in the conditions of the north-eastern Forest-Steppe of Ukraine.
The study finds out that the duration of the growing season of the studied maize hybrids depended on their biological characteristics and fertilization methods. In the early-ripening hybrid DKC 3050, 89-108 days passed from emergence of maize seedlings to physiological maturity; in the medium-early hybrid DKC 3730, 95-112 days; and in the mid-ripening hybrid DKC 4178, 99-115 days. The application of nitrogen fertilizers prolonged the vegetation of maize plants by 10-17 days, depending on the rate and form of application.
The influence of mineral nitrogen forms on the formation of maize crops is revealed. The highest plant density indicators at the time of harvesting are recorded when anhydrous ammonia is applied: 71.5-72.6 thousand/ha in the hybrid DKC 3050; 71.4-72.8 thousand/ha in the hybrid DKC 3730 and 71.8-73.2 in the mid-ripening hybrid DKS 4178. The variants with Urea and UAN-32 were inferior to anhydrous ammonia in this indicator.
This paper investigates the peculiarities of linear growth of maize plants under the influence of mineral nitrogen rates and norms. At the initial stages of vegetation VE-V5, no significant effect of fertilization on plant growth was observed. In the V8 phase, an increase in the linear dimensions of maize was noted, with the plants in the variants with the application of UAN-32 and anhydrous ammonia having a height of 76.0-87.5 and 75.3-87.1 cm, respectively, while with the urea application, the height of the plants was 72.6-86.6 cm. In the phase of ejection of panicles VT, the highest plant height was observed with the urea application - 240.3-263.3 cm, slightly lower in the variants with the application of anhydrous ammonia - 242.6-259.9 cm and the lowest with UAN-32 - 239.5-249.3 cm.
A close direct correlation between plant height and the rate of mineral nitrogen application is established. The correlation coefficient is 0.8960-0.9985.
The study reveales the influence of maize fertilization methods on the formation of photosynthetically active leaf apparatus. The maximum leaf area in maize crops is observed in the phase of panicle ejection (VT) and amountes to 40.9-45.0 thousand m2/ha when anhydrous ammonia is applied, 41.2-45.8 thousand m2/ha in variants with urea and 40.0-44.8 thousand m2/ha when UAN-32 is used.
This paper demonstrates the dependence of NDVI indicator of maize crops of hybrids of different maturity groups on fertilization methods. The highest values of the vegetation index are recorded in the period of panicle ejection (VT) - 0.62-0.78.
The study records that the maximum chlorophyll in plants, according to the N-Tester BT device, is observed in the phase of panicle ejection (VT) - 430-760. Variants with the application of prolonged-acting forms of nitrogen (anhydrous ammonia and urea) are characterised by a better intensity of green colour (higher chlorophyll content) compared to UAN-32.
The author finds out that in maize hybrids of different maturity groups, the number of rows in the cob and the number of grains in a row does not depend on the norms and forms of mineral nitrogen application, but is determined by nitrogen nutrition in general. However, the formation of the mass of 1000 seeds depends on the characteristics of the nitrogen used - the highest rates were at the application of 150 kg/ha of a.s. - 291-318 g.
The paper demonstrates influence of maize fertilization methods on the formation of grain productivity of crops. The highest yield over the years of research is recorded for variants with 150 kg/ha of nitrogen fertilizer - 8.90-10.3 t/ha, depending on the form of nitrogen and the studied hybrid.
The author finds out that the protein content in maize grain is determined by nitrogen nutrition - with an increase in the rate of nitrogen application, its growth is observed. The highest rates are in the variants with anhydrous ammonia (10.7-12.2%) and urea (10.5-12.2%), while in the variants with UAN-32 its content is 9.29-11.5%.
The study identifies the best variants of the experiment in terms of economic efficiency. The highest rates of profitability of 26.8-68.0% are observed when using average rates of mineral nitrogen (150 kg/ha). Among the studied forms of nitrogen, anhydrous ammonia is the best, with a profitability level of 61.3-68.0%.
The best indicators of energy efficiency of maize fertilization methods are recorded in the experimental variants using anhydrous ammonia - 5.58-6.47, and among the studied rates of mineral nitrogen application - at 150 kg/ha of a.s. - 5.92-6.47, depending on the form of nitrogen.
