Case of a stronger capability of maize seedlings to use ammonium being responsible for the higher 15N recovery efficiency of ammonium compared with nitrate.

Aims: Matching a crop's nitrogen (N) preference with the specific form of N is critical to enhance N recovery efficiency (NRE). Many studies show that maize (Zea mays L.) has a preference for NH₄⁺ uptake over NO₃⁻, but the contribution of this preference to NRE is unclear. This study evaluated the utilization of ammonium (NH₄⁺) and nitrate (NO₃⁻) by maize and its relationship with NRE. Methods: Maize (cv. 'Zhengdan 958') seedlings were grown in a soil culture experiment with ¹⁵NH₄⁺ or ¹⁵NO₃⁻ applied to sterilized or non-sterilized soils, and in a hydroponic experiment supplied with NH₄⁺ or NO₃⁻. We recorded maize root and shoot growth and N uptake, and the distribution of ¹⁵N-labeled N in the soil–plant system. Results: Ammonium application enhanced maize root and shoot growth and N uptake compared with those of NO₃⁻-treated plants in both culture systems. This enhancement by NH₄⁺ was further promoted in sterilized soil. More applied N remained in soil supplied with NO₃⁻ than with NH₄⁺ after seedling harvest. The NRE of NH₄⁺ in maize was significantly higher than that of NO₃⁻, while a similar proportion of applied N was lost with NH₄⁺ or NO₃⁻supply. Conclusions: Ammonium supply enhances maize growth and NRE compared with NO₃⁻ under the present experimental condition, which may be attributable to the superior capability of maize to utilize NH₄⁺. [ABSTRACT FROM AUTHOR]