Comparing localized application of different N fertilizer species on maize grain yield and agronomic N-use efficiency on a calcareous soil

Localized phosphorus (P) plus nitrogen (N) fertilization results in an ammonium-dependent enhancement of maize (Zea mays L) growth and nutrient uptake at the seedling stage. However, how N forms affect maize growth, grain yield components, and agronomic N-use efficiency (AEN) in field conditions is not fully understood. A 2-year field experiment with maize growing on a calcareous soil was conducted with localized application of NH4+-N, P (superphosphate), P plus either NO3--N, NH4+-N or NH4:NO3 (1:1) at sowing and jointing as well as no N and P as control (CK). The results showed that localized supply of NH4+ -N+P as starter fertilizer and as side-dressing at jointing increased shoot dry weight and N and P accumulation at different stages when compared with CK, localized application of P or NO3--N + P in 2012 and 2013, even when NH4+-N was applied with nitrate (1:1, meaning NH4+-N was reduced by 50%) or NH4+-N was supplied without P. Plant growth rate (PGR) and dry matter distribution in ear at grain filling (25 days after the onset of anthesis) were higher in localized NH4+-N, NH4 :NO3 (1:1) + P and NR4+-N + P than CK, localized P and NO3--N + P treatments. The grain yield and N concentration in grain increased by 10-48% and 4-27%, respectively, in localized NH4+-N, NH4:NO3 (1:1) + P and NHe-N + P treatments compared with CK, localized P and NO3--N + P in two years. The AEN and kernel number per ear were enhanced by supply of NH4+-N, NH4:NO3 (1:1) + P or NH4+-N + P, but not with NO3--N + P. There was a positive linear correlation between kernel number per ear and PGR. The NH4+-N supply in localized NH4+-N + P treatment accounted for more than 50% of variation in PGR, shoot dry matter and grain yield at maturity in 2012 and 2013. The results indicate that localized application of P with NH4+-N enhances maize grain yield, kernel number per ear and agronomic N-use efficiency on calcareous soil via improving post-anthesis growth, dry matter distribution and nutrient accumulation. (C) 2015 Elsevier B.V. All rights reserved.