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To improve crop nitrogen recovery efficiency (NRE), plants must be supplied with their preferred form of nitrogen (N). However, whether pH affects crop N-form preference remains unclear. Here, we aimed to explore how maize (<i>Zea mays</i> L.) preference for NH₄⁺ and NO₃⁻ is affected by pH and to determine the critical pH controlling this preference. Maize plants were grown with NH₄⁺ or NO₃⁻ in different soils (pH 4.32–8.14) and nutrient solutions (pH 4.00–8.00). After harvest, plant dry weights, N content, N uptake, NRE, soil pH, and exchangeable aluminum (Al) were measured. Compared with the effect of NO₃⁻, NH₄⁺ decreased maize dry weight, N uptake, and NRE by 28–94% at soil pHs of 4.32 and 4.36 and a solution pH of 4.00, whereas it increased these parameters by 10–88% at soil pHs of 6.52–8.02 and solution pHs of 7.00 and 8.00. NO₃⁻ increased soil pH and decreased soil exchangeable Al content at soil pHs of 4.32–6.68. Critical soil and solution pHs for changing plant growth and N uptake preference for NH₄⁺ vs. NO₃⁻ ranged from 5.08 to 5.40 and from 5.50 to 6.59, respectively. In conclusion, the preference of maize seedling growth and N uptake for NH₄⁺ vs. NO₃⁻ mainly depends on the pH of the growth medium, and maize seedlings generally prefer NO₃⁻ in strongly acid soils but NH₄⁺ in neutral to alkaline soils.