Effects of Rhizobium inoculation and integrated fertilization on the nutritional composition of maize (Zea mays L.) in northwest Ethiopia

Micronutrient deficiencies remain a major public health challenge in Ethiopia, largely due to reliance on cereal-based diets with low nutrient density. Microbial biofortification using Rhizobium offers a sustainable strategy to enhance nutrient content in staple crops. This study aimed to evaluate the effect of Rhizobium inoculation and chemical fertilizer application on nutritional composition of maize in northwest Ethiopia. A randomized controlled field trial was conducted across three districts (Baso Liben, Debre Elias, and Womberma) during the 2024 cropping season. Seeds of the ‘BH-661’ maize variety were evaluated under three treatments: Treatment 1 (T1): recommended full-dose chemical fertilizer (100 kg DAP ha −1 + 50 kg urea ha −1 ; Treatment 2 (T2): Rhizobium inoculation without chemical fertilizer; and Treatment 3 (T3): Rhizobium inoculation combined with half-dose chemical fertilizer (50 kg DAP ha −1 + 25 kg urea ha −1 ). Proximate composition and micronutrient levels were analyzed using standard laboratory methods, including atomic absorption spectrophotometry. Data were analyzed using two-way mixed-effects analysis of variance, with statistical significance declared at p < 0.05. Compared to Treatment 1, Treatment 3 significantly increased crude protein (11.26 vs. 8.77%, F(2,4) = 45.970, p = 0.002, ηp 2 = 0.958), carbohydrate (58.26 vs. 56.68%, F(2,4) = 7.51, p = 0.044, ηp 2 = 0.790), crude fiber (2.14 vs. 2.07%, F(2,4) = 265.101, p < 0.001, ηp 2 = 0.993), ash (1.27 vs. 1.15%, F(2,4) = 5.84, p < 0.045, ηp 2 = 0.745), iron (20.67 vs. 18.92 mg/kg, F(2,4) = 3.77, p = 0.038, ηp 2 = 0.770), and zinc (18.13 vs. 14.75 mg/kg, F(2,4) = 52.24, p < 0.001, ηp 2 = 0.984). The combined application of Rhizobium inoculation and reduced-rate chemical fertilizer therefore improved selected macro- and micronutrient concentrations of maize grain, particularly, crude protein, carbohydrate, crude fiber, ash, iron and zinc contents. These results suggest that integrated microbial and mineral fertilization may serve as a promising agronomic biofortification strategy.