A study evaluated the effectiveness of Methylobacterium symbioticum as a foliar inoculant in enhancing nitrogen fixation and lettuce dry matter yield. The inoculant, marketed as BlueN, was tested in a factorial experiment with four nitrogen rates (0, 25, 50, and 100 kg ha⁻¹ of N) and four lettuce growing cycles. The results showed that the inoculant had a minimal effect on nitrogen fixation and lettuce dry matter yield (DMY), with significant differences observed only in the second growing cycle. The DMY ranged from 9.9 to 13.7 g pot⁻¹ in pots receiving the inoculant and 9.9 to 12.6 g kg⁻¹ in untreated pots. In contrast, soil-applied nitrogen significantly increased DMY and tissue nitrogen concentration across all cycles. The apparent nitrogen recovery (ANR) was highest at the highest nitrogen rate (100 kg ha⁻¹), while apparent nitrogen fixation (ANF) was very low, indicating limited nitrogen fixation by the inoculant. The study concluded that the inoculant had a limited effect on nitrogen fixation and DMY, likely due to a lack of specificity between the microorganism and lettuce. Further research is needed to determine the inoculant's effectiveness in other crops and under different conditions.A study evaluated the effectiveness of Methylobacterium symbioticum as a foliar inoculant in enhancing nitrogen fixation and lettuce dry matter yield. The inoculant, marketed as BlueN, was tested in a factorial experiment with four nitrogen rates (0, 25, 50, and 100 kg ha⁻¹ of N) and four lettuce growing cycles. The results showed that the inoculant had a minimal effect on nitrogen fixation and lettuce dry matter yield (DMY), with significant differences observed only in the second growing cycle. The DMY ranged from 9.9 to 13.7 g pot⁻¹ in pots receiving the inoculant and 9.9 to 12.6 g kg⁻¹ in untreated pots. In contrast, soil-applied nitrogen significantly increased DMY and tissue nitrogen concentration across all cycles. The apparent nitrogen recovery (ANR) was highest at the highest nitrogen rate (100 kg ha⁻¹), while apparent nitrogen fixation (ANF) was very low, indicating limited nitrogen fixation by the inoculant. The study concluded that the inoculant had a limited effect on nitrogen fixation and DMY, likely due to a lack of specificity between the microorganism and lettuce. Further research is needed to determine the inoculant's effectiveness in other crops and under different conditions.