Optimal nutrient application timing can be hard to nail down. Should you apply everything at the beginning of the season? Sidedress? If so, when? Many people wonder about nitrogen applications late in the season, even after post-tassel, as a way to increase yield. The basic thinking is that the crop still needs to take up half of its total N at this point in the growing season.
The truth is, in locations with a shorter growing season, like Minnesota, we have no evidence that post-tassel N applications have any advantage.
Research by the University of Minnesota evaluated nitrogen application timing and its effect on different soil types across Minnesota to evaluate differences in economic optimum N rate and see whether split applications were beneficial at certain times throughout the season.
It showed that if conditions dry out in July or August, you can actually end up reducing corn yield because the yield potential of the crop is either compromised if there was no sufficient N for the crop earlier in the growing season or the sidedress N does not get to the root because of the lack of moisture.
The only situation where a post-tassel application before R1 may be beneficial to increase yield is if the crop is severely limited by lack of nitrogen. In those cases, however, carefully evaluate the potential return on investment, as the nitrogen application can’t make up for the yield potential already lost.
Key Takeaways on Nitrogen Application Timing
- Single pre-plant applications are often as good, if not better than split applications in fine-textured soils.
- For fine-textured soils, split applications work consistently well if done up to about V6 development stage. Applications later in the season can result in yield reduction if the crop experienced insufficient N availability earlier or if weather conditions turn dry and the applied N doesn’t get incorporated into the root zone.
- Split applications are superior to single applications in irrigated coarse-textured soils. This is because coarse-textured soils have high potential for nitrogen loss early in the growing season and the soil organic matter is low, thus the soil has little capacity to buffer nitrogen loss. Another advantage is that split applications can typically be done easily and inexpensively through fertigation.
- Post-tassel applications of nitrogen are highly unlikely to produce a grain yield increase.