Nitrogen applications made close to silking: Implications for yield formation in maize

Given the growing interest in late N applications made at vegetative stages just prior to silking (R1), there is a need to characterize how yield formation in maize responds when a small amount of N is applied early in the season, and the bulk of N fertilizer is delayed to vegetative stages close to R1. To understand how the development of kernel number (1(N) and weight (KW) are affected by this shift in fertilizer N availability, a two-year split-plot experiment was conducted. The main plot factor consisted of five pre-plant N rates (in kg N ha(-1): 0, 80, 140, 200, 260) and a split-plot factor consisted of an N application at V13, 9 or 11 days before R1. Split-plots either received no in-season N or a non-limiting N rate such that the total N applied equaled 260 kg N ha(-1). At 0 kg N ha(-1) pre-plant, N stress significantly reduced radiation use efficiency and crop growth rate during the critical period around R1, which in turn reduced potential kernel number (pKN) and potential kernel sink capacity (pKW) by the start of the linear phase of grain-fill. When 80 or 140 kg N ha(-1) was applied pre-plant, N stress was not detected at or prior to the start of the linear phase of grain-fill, but reductions in KN and/or KW occurred later, within 30-40 days of R1. The V13 N application increased grain yield at the lower pre-plant N rates by either: i) preventing reductions in pKN and pKW at the start of the linear grain-fill period or by ii) better maintaining KN and KW during the linear phase of grain-fill. At maturity grain yield in the split-N treatments receiving 260 kg N ha(-1) at V13 was statistically similar to 260 kg N ha(-1) applied pre-plant, but maize N uptake increased in response to the V13 N application only once the crop became N deficient. Overall, these results provide a physiological understanding of the impact of late N applications on yield formation in maize and can assist in the further development of N management strategies that better synchronize fertilizer N supply with crop N demand.