Supplemental Late-Vegetative Nitrogen Applications for High-Yield Corn: Agronomic, Economic and Environmental Implications with Modern Versus Older Hybrids

It has been proposed that modern hybrids continue to accumulate N longer into the growing season, and for this reason it would be beneficial to ensure soil mineral N availability by way of intentional supplemental, late-season (e.g., V12 to V14) N application. In 2014 (the first year of this experiment), we began working toward answering the questions: (1) Are modern hybrids more likely to respond to intentionally very late-vegetative N applications than hybrids of 20 years ago? and (2) What are the physiological reasons for these differences if the modern hybrids are more responsive? To this end, we compared four hybrids across six N rate and timing combinations. The hybrids included two modern (P1360 and P1498) and two released in the early-mid 1990s (Pioneer hybrids 3335 and 3394). The N rates (0, 140, 180, and 220 lb N/A in addition to a starter N application of 25 lb N/A) were either applied only at V3 or split between V3 and a 40 lb/A application at the V13 stage.

The 2014 weather was characterized by cool temperatures and ample precipitation in Indiana. We had excellent population establishment and short anthesis-silking intervals during flowering. Additionally, the plants retained their leaf area index (LAI) long into their reproductive stages; both LAI and leaf chlorophyll (SPAD) for all hybrids persisted into R4, with the exception of the 0N plots. P1498 consistently had a significantly higher LAI throughout the reproductive stages. P1360 was significantly lower in SPAD readings. The modern hybrids had significantly higher total biomass accumulation at R1, and the leaf to stem ratio did not differ across the four hybrids.

As would be expected, average yields with the two modern hybrids were about 40 bu/A higher. P1498 was the only hybrid with a significant hybrid x N treatment interaction for final grain yield; the late-split N treatments (180L and 220L) were the highest yielding. For that hybrid, corn yields increased from 207 to 215 bu/A when the V3 sidedress N rate increased from 140 to 180 lb, but corn yields were even higher (233 bu/A) when the 140 sidedress was followed by a 40 lb N application at V13. We have yet to complete the R6 stage N analyses and N efficiency calculations.