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

Purpose 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. Materials and methods In this 30-day pot experiment, acid soil (pH 4.54; base saturation, 27%) with or without maize plants was supplied with N-15-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)). Results and discussion 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. Conclusions 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.

Automated summary

Maize plants prefer NO3-, which enhances the nitrogen recovery efficiency in acid soil by alleviating aluminum toxicity through increasing soil pH. Lime application further improves maize biomass and nitrogen recovery efficiency by reducing soil exchangeable aluminum concentration.