(Professor Jeff Coulter discusses the latest in corn agronomy at the field day)
Written by Jonathan Eisenthal
The annual Agronomy Field Tour at the University of Minnesota Southern Outreach and Research Center in Waseca brought out University of Minnesota researchers to discuss the latest research impacting on-farm practices. Here are some highlights:
Assistant Professor Fabian Fernandez presented the latest work on nitrogen rates.
Taking the average of all sites, the Maximum Return to Nitrogen (MRTN) for Minnesota currently stands at 130 pounds per acre for corn-soybean rotations and 165 pounds per acre for continuous corn. Fernandez cautioned that the MRTN calculator presents a distribution of Economically Optimal Nitrogen Rates (EONRs) and growers should pay attention to variables like planting date and weather conditions to make the best estimate for what will work in their fields.
“EONR is a management concept that is good for the pocketbook and good for the environment,” Fernandez told an audience of about a hundred farmers, crop consultants and agronomy students. “You are putting only as much fertilizer as the crop can use, so less fertilizer can escape.”
For example, the EONR for a site near Wells was 127 pounds, which produced 187 bushels per acre. When you apply rates above the EONR, it produced few additional bushels, according to Fernandez.
Cover crops impact on herbicide-resistant weed
For its weed prevention abilities, Associate Professor Gregg Johnson made a case for rye grass as the workhorse cover crop, providing lots of above ground biomass. But when it comes to more invasive weeds, like Palmer Amaranth, pre-emergent herbicides may still be necessary—even if they impact cover crop growth.
“This will ding up your covers, no doubt,” he said, but, he also argued the cover crops may still offer enough of a weed-preventing presence to make seeding them worth it.
Regardless, he strongly urged growers do not reduce herbicide rates for greater chance of cover crop survival (or to reduce input costs). Johnson said it won’t help the covers much, but it will hasten the development of resistant weeds.
Professor Jeff Coulter took attendees through some of the latest corn agronomy findings, concentrating on information that has bearing on this year’s later planting.
Among the outcomes of the late planting and the shorter growing season, farmers can expect wetter corn this fall. By the time corn reaches maturity, it will have very little adequate drying time in the field. Beyond mid-October, the short day length and lack of heat units will limit the potential for in-field grain dry-down (0 to 0.33 percentage points per day). Thus, growers should be prepared to once again deal with wetter grain at harvest.
One of the key elements of stand establishment is plant population. Coulter notes that many farmers target 34,000 plants per acre. This information is important when assessing stand damage from hail, which has impacted Minnesota corn fields.
Coulter says, “If we look at data from a lot of trials, it shows that a stand of 28,000 plants per acre without a lot of large gaps will produce about 95 percent of maximum yield. And, even if the stand is just 24,000 plants per acre, it will still produce about 91 percent of maximum yield.”
Stand variability caused by the tumultuous planting season will also have an impact. “A plant that’s two leaf stages behind the others in the row, at this time of year, will only yield about one-half of what it should,” said Coulter.