How N fertilizer side-dressing timings mediate fertilizer N fates in maize grown in a Mollisol

A field micro-plot experiment with nitrogen isotope (15 N) labelling was performed to study the impacts of the timing of aside-dressed Napplication on urea-15 N in amaize-soil system. The treatments comprised three application timings, each of which consisted of the identical total rate of N, i.e. 280kg ha−1. In all treatments, 40% of the Nwas used theday prior to sowing, and the rest was used either at the jointing stage (V6) (N1), at the bell stage (V12) (N2) or at the tasselling stage (VT) (N3). The results indicated that the grain yields increased in both the N1 and N2 treatments compared with the N3 treatment. Asplit application of Nat the bell stage significantly raised the percentage of Nderived from fertilizer N(Ndff) compared to the two other side-dressed Napplication timings. The 15 N recovery efficiencies for the N2 and N1 treatments were 10% greater than the N3 treatment. The possible Nlosses in the N2 treatment were lower than those in the other treatments. Therefore, Nside-dressing at the bell stage is an alternative and sustainable management strategy for maize production and NUE in spring maize cropping systems.