The field experiment was performed in 2019–2021 at the Experimental Station of Vytautas Magnus University Agriculture Academy (54°52′ N, 23°49′ E). The soil of the experimental field was Endohipogleyic-Eutric Planasol. The studied factors were: Factor A—different nitrogen fertilizer rates: (1) 100 kg N ha⁻¹; (2) 140 kg N ha⁻¹; (3) 180 kg N ha⁻¹; Factor B—the use of urease inhibitors (UI) and biological preparations (BP): (1) urease inhibitors (UI) and biological preparations (BP) were not used; (2) Urease inhibitor (UI ATS)—ammonium thiosulfate—[(NH₄)₂S₂O₃ 12-0-0-26S]; (3) Urease inhibitor (UI URN)—N-butyl-thiophosphorus triamide (NBPT) and N-propyl-thiophosphorus triamide (NPPT); (4) Biological preparation (BP HUM)—suspension of humic and fulvic acids; (5) Biological preparation (BP FIT)—Ascophyllum nodosum suspension. Our studies showed that the highest yield of maize grain (8.9–12.0 t ha⁻¹) was obtained by fertilizing with N180 and using the urease inhibitor ammonium thiosulfate (ATS). ATS significantly increased corn grain yield in all backgrounds of nitrogen fertilization. The investigated urease inhibitors and biologics had a higher and more significant (p < 0.05) effect on maize grain yield when fertilized with N₁₀₀ nitrogen. The increase in nitrogen fertilizer rates had an effect on maize grain yield, with the largest increase in yield being found in the increase in nitrogen rate from N₁₀₀ to N₁₄₀, and the increase in rate to N180 was less effective. The maximum mass of 1000 grains (323.5 g) was determined in 2019 by fertilization with N180 and use of the urease inhibitor UI URN. The urease inhibitor UI ATS was more effective when fertilized with lower rates of N₁₀₀ and N₁₄₀. Positive, moderate, strong and very strong, statistically significant correlations (r² = 0.48–0.91) were most often found between the latter indicators and nitrogen fertilizer rates throughout the study year. The largest amount of grain (497 units) in the cob was determined in 2019, using fertilization with N₁₄₀ and UI ATS, but no significant differences were found between the different fertilizer rates and the tested preparations. These results suggest that urease inhibitors and biologics can reduce dependence on nitrogen fertilizers and increase maize yield, a technology that should be practiced by maize growers.

After evaluating the ecological and economic aspects, it is predicted that the use of urease inhibitors and biological preparations should reduce the risk of nutrient leaching by using fertilizers containing amide, ammonium, and nitrate forms of nitrogen and would increase nitrogen use efficiency. Moreover, with lower nitrogen fertilizer rates, it would be possible to achieve or even increase planned maize biomass yield. The field experiment was performed in 2019–2021 at the Experimental Station of Vytautas Magnus University Agriculture Academy. The soil of the experimental field was Endohipogleyic-Eutric Planasol. The aim of this study was to investigate the effect of urease inhibitors and biological preparations in combination with nitrogen fertilizers on the productivity of aboveground maize (Zea mays L.) biomass. A two-factor experiment was carried out: factor A included nitrogen fertilizer rates of (1) 100 kg N ha⁻¹, (2) 140 kg N ha⁻¹, and (3) 180 kg N ha⁻¹; and factor B included the use of preparations of (1) no use of urease inhibitors (UIs) and biological preparations (BPs) (control), (2) the urease inhibitor ammonium thiosulphate (UI ATS), (3) the urease inhibitor (UI URN)—N-Butyl-thiophosphorus triamide (NBPT), (4) the biological preparation of suspension of humic and fulvic acids (BP HUM); and (5) the biological preparation (BP FIT) of suspension of Ascophyllum nodosum The studies showed that the dry matter yield of maize was significantly increased not only by increasing nitrogen fertilizer rates but also by the use of UIs and BPs. The highest dry matter yield of maize (24.1 t ha⁻¹) was obtained with N₁₈₀ fertilizer and UI ATS. UI ATS significantly increased the dry matter yield of the aboveground maize in all nitrogen fertilization backgrounds. The UIs and BPs tested had a greater and significant (p < 0.05) effect on the dry matter yield of maize at lower rates of N₁₀₀ and N₁₄₀ nitrogen fertilizer. Increasing nitrogen fertilizer rates up to N₁₈₀ had a positive significant effect on dry matter yields of the aboveground part of maize, its cobs, leaves, and stems. Positive, moderate, strong, and very strong correlations were found in most cases between the latter variables. These correlations were statistically significant (r² = 0.62–0.98). The UIs and BPs increased the efficiency of nitrogen fertilizer; therefore, the lower rates of nitrogen fertilizer (N₁₀₀ and N₁₄₀) could be used to produce maize productivity the same as that obtained with a high rate of nitrogen fertilizer (N₁₈₀).