Maize Responses to Fertilization, Hydrogel, and Silicon Addition Under Contrasting Soils and Climate Conditions in the Nordic–Baltic Region

This two-year study (2023–2024) evaluated maize (Zea mays L.) responses to mineral, organic, and integrated fertilization with hydrogel and silicon at two contrasting sites in Central Lithuania. Thirteen treatments were tested to assess grain yield, total aboveground biomass (TAB), N uptake, soil mineral N dynamics, and agronomic N use efficiency (AEN). AN2 (170 kg N ha−1) produced two-year mean grain yields of 7.33 and 5.73 t ha−1 at Akademija and Ruoščiai, respectively. AN1 + PCM (90 kg mineral N + 80 kg manure N ha−1) yielded 6.55 and 5.14 t ha−1. Both treatments received 170 kg N ha−1, and their grain yields did not differ significantly in the within site-year comparisons (Duncan’s test, p > 0.05), although their P and K inputs differed. The two-year mean AEN values for AN2 and AN1 + PCM were 12.41 and 7.86 kg grain kg−1 N at Akademija, and 9.71 and 6.27 at Ruoščiai, respectively. Organic-only fertilization resulted in lower mean grain yields than AN2, but the year-to-year responses varied, so the cumulative effects cannot be inferred. Across both seasons, TAB and grain yield were lower at Ruoščiai than Akademija by 23.1–26.0 and 18.9–25.8%, respectively; these site differences cannot be attributed to soil texture alone. More residual mineral N remained at Ruoščiai in 2023, but this does not directly measure crop N recovery. Hydrogel and silicon provided minor treatment- and year-dependent numerical yield increases, with no consistent advantage.