You read many articles about comparing one nitrogen rate to another. You also read articles about picking the seeding rate that delivers the correct final harvest population to either reach maximum yield or net the most return. The fact is, you don’t make either one of these decisions in a vacuum. What happens when you look for the nitrogen rate and population combination that will net the highest net return in a year like 2018, when every dollar counts?
Jim Schwarz, director of Beck’s Practical Farm Research program and Agronomy division, and his staff decided to attempt to answer that question through a PFR trial in 2016 and 2017. They wanted to be able to provide an answer for farmers asking that question in 2018. Jon Skinner, a Beck’s field agronomist, worked closely with this study.
In Beck’s 2017 PFR Summary book, Skinner notes that they compared three different nitrogen rates and three populations across two hybrids. One hybrid was selected because it tends to respond with more yield at higher populations. The other hybrid typically responds with more yield as nitrogen rates increase. The trial was repeated at three locations: central Illinois, Ohio and Iowa. The same study was carried out in both 2016 and 2017.
Two years in a row, data averaged over all three locations indicated that the economic optimum nitrogen rate was 190 pounds per acre. The economic optimum seeding rate was 30,000 seeds per acre. This held true regardless of whether the hybrid liked more N or a higher population, Skinner says.
The hybrid that responds to higher population picked up yield in most cases as population increased from 30,000 to 38,000 plants per acre. For example, in 2017 at 230 pounds of nitrogen per acre, this hybrid yielded 218.6 bushels per acre at the 30,000 seeding rate and 221.6 bushels per acre at the 38,000 seeding rate. The increase didn’t cover the cost of seed, Skinner notes.
Likewise, the hybrid that prefers more nitrogen increased yield from 222.4 to 230.4 bushels per acre at 34,000 seeds per acre in 2017. However, even that 8-bushel-per-acre increase still resulted in nearly $4 less return per acre.
Skinner says the study reflects meager commodity prices for corn and relatively strong prices for nitrogen. The study assumed you could sell corn for $3.86 per bushel. Nitrogen was priced at 44 cents per unit. Liquid nitrogen was applied in this study. Seed prices were just over $300 per bag for each hybrid.
“Both the high-response-to-population hybrid and the high-response-to-nitrogen hybrid increased yield when their respective change was made,” Skinner says. “Unfortunately, there was not enough of a yield response to overcome the increased cost of production.”
Changes in the selling price of corn or the cost of nitrogen per unit could affect the results in the future.