The combined use of organic and potassium fertilizers leads to a significant increase in the levels of available ammonium (NH₄⁺) and nitrate (NO₃⁻) in the soil. This experiment was conducted in a field at the Faculty of Agriculture, University of Gezira—the Gezira region being a major producer of yellow maize (*Zea mays* L., variety 113) in Sudan. The study aimed to evaluate the impact of organic and potassium fertilization on available soil ammonium and nitrate content, as well as on grain protein percentage and yield. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replicates, utilizing a split-plot arrangement. It involved two factors: potassium fertilizer (potassium sulfate at rates of 0, 100, and 200 kg K/ha) and organic fertilizer (sheep and cattle manure at rates of 0, 20, and 25 tons/ha). The results showed that the addition of sheep manure significantly increased the available ammonium content during the flowering and harvest stages, reaching 8.55 and 8.72 mg kg⁻¹ soil, respectively. This compared to 7.08 and 7.36 mg kg⁻¹ soil for the cattle manure treatment, and 6.22 and 6.56 mg kg⁻¹ soil for the control. However, the treatment did not significantly affect soil nitrate content at either stage or grain protein content. The third level of potassium fertilizer had a significant effect on available ammonium during the flowering and harvest stages, resulting in levels of 8.25 and 8.06 mg kg⁻¹ soil, respectively, compared to 6.16 and 6.94 mg kg⁻¹ soil for the first potassium level. Meanwhile, the interaction between organic manure and potassium fertilizer showed no significant effect on available ammonium, soil nitrate content at either stage, or grain protein content. The combination of organic amendments and potassium fertilizers creates an optimal soil environment that enhances microbial activity and nutrient retention capacity, leading to maximum levels of available inorganic nitrogen (NH₄⁺ and NO₃⁻). Effect on protein content in yellow maize grains.