The preference of maize plants for nitrate improves fertilizer N recovery efficiency in an acid soil partially because of alleviated Al toxicity

NH4+ and NO3− are the two main inorganic N forms available for plant growth, and NO3− is the preferred N source of maize (Zea mays L.) grown in acid soils. However, the mechanisms for this preference and its contribution to fertilizer N recovery efficiency (FNRE) remained unclear. In this 30-day pot experiment, acid soil (pH 4.54; base saturation, 27%) with or without maize plants was supplied with 15N-labeled NH4Cl (20.12 atom % excess), NaNO3 (30.15 atom % excess), or urea (20.10 atom % excess) at the rate of 200 mg N kg−1 without or with liming (1.2 g CaCO3 kg−1). Without liming, maize biomass and FNRE were higher under NO3− or urea than under NH4+. Lime increased the maize biomass and FNRE by 421–835% under NH4+ and by 30–112% under NO3− or urea. Without lime, the maize shoot Al concentration was much lower under urea or NO3− than under NH4+, because NH4+ decreased soil pH by 0.35 units and increased soil exchangeable Al concentration by 4–11%. Lime increased soil pH by 0.1–0.3 units and decreased soil exchangeable Al concentration by 25–57%. Among various treatments, the biomass of maize plants was negatively correlated with soil exchangeable Al concentration. The preference of maize plants for NO3− improves the FNRE of maize in acid soil partially due to alleviated Al toxicity as a result of soil pH increase.