Can Late-Split Nitrogen Application Increase Ear Nitrogen Accumulation Rate During the Critical Period in Maize?

Ear and plant growth rates during the critical period (CP) in maize (Zea mays L.) are known to affect grain yield, but little is known about how CP ear N accumulation and vegetative N dynamics respond to N fertilizer timing. In a 2-yr study, the influences of in-season split N applications on ear N accumulation rate (ENAR), ear growth rate (EGR), and stem and leaf dry matter and N accumulation were determined from 14 d before to 14 d after silking (R1). Up to eight N rate and timing treatments (0, 110, 155, 200, and 245 kg N ha(-1), either applied in a single application or with the last 45 kg ha(-1) delayed until V12) were imposed on four hybrids: two modern (P1498HR and P1360HR) and two released 20 yr ago (3335 and 3394). Both EGR and ENAR during the CP were very stable among N treatments and were only uniquely influenced by the zero N after R1. Both leaf N and ear N contents during the CP were highly conserved and were not affected by the timing of N application. Late-split N application resulted in less stem N remobilization in the 14 d after R1 than a single N application at moderate and high N rates. Despite sporadic hybrid group differences in EGR as the CP period progressed, the lower yielding older hybrids realized consistently lower presilking ENAR and higher postsilking ENAR. These data suggest that late-split N applications near the CP onset benefits stem N content, which may enhance N source capacity for developing ears but does not increase either ear or leaf N content during the CP.