Late-Split Nitrogen Applications Increased Maize Plant Nitrogen Recovery but not Yield under Moderate to High Nitrogen Rates

Theoretically, N losses are reduced by synchronizing fertilizer additions with plant uptake requirements. We investigated the impacts of supplemental, late-season N applications on nitrogen fertilizer recovery efficiency (NRE), and N accumulation and partitioning in maize (Zea mays L.) at silking (R1) and physiological maturity (R6). Also tested was whether modern hybrids responded differently to split-N applications compared to hybrids released 20 yr ago. We compared 3 to 4 N rates ranging from 0 to 245 kg N ha(-1) applied either in a single application at V3, or split with the last 45 kg N ha(-1) delayed until V12, over 3 yr. Two newer hybrids (2012 and 2014) and two 1990 era hybrids (1991 and 1995) were compared at all N treatment combinations. Additional plant N accumulation following late-split N applications was already apparent at R1, particularly in stems. Late-split N application increased both whole-plant R6 N accumulation and NRE through higher post-silking N uptake. However, these benefits were rarely accompanied by increased grain yields. We found little evidence of differential hybrid responses to N rate or timing treatments. Principal component analysis revealed that the most consistent predictor of high postsilking N uptake was lower N remobilization during grain-fill; these had a strong inverse relationship. Therefore, gains from N management programs aiming to increase post-silking N uptake are most likely in environments where whole-plant N accumulation at R1 (and, consequently, potential N remobilization) is reduced. Further studies of late-split N approaches are most warranted at lower total-season N rates.