About this time of year, farmers take a look forward at the coming year’s production, but it might be too early to pin down exactly how much nitrogen will go on corn fields. Ohio State researchers have been studying ways to re-evaluate crop needs during the growing season to give plants all the nitrogen they can use without applying extra. Not only is excess nitrogen expensive, it also can cause water quality problems. “The key here is maximizing our nitrogen efficiency,” says Elizabeth Hawkins, field specialist with Ohio State University Extension. “We want enough there so plants can use it, but not be at risk for losing it.”

When nitrogen is applied before plants are ready for it, the nitrogen doesn’t always wait patiently in the soil. Sunlight and heat contribute to volatilization losses into the air, rain can increase losses through denitrification, and wet soils can allow nitrogen to leach away into drainage water and groundwater. Meanwhile, weather is also affecting the development of the crop and its nitrogen requirements. “It’s really easy to look back and say what we should have done,” Hawkins says.

To help farmers make more efficient nitrogen application decisions, Hawkins and her fellow researchers are studying the information available throughout the growing season. For instance, they’re using soil tests to see how quickly nitrogen changes in soils, and they’re monitoring plant health with tissue testing. Going forward, they’re also planning to collect weather data and soil moisture data to pair up with soil test data collected through the season. The idea is to use that data to more accurately determine how much nitrogen needs to be applied and when it should go on.

Waiting until growth stage VT, just before tasseling, for the late season nitrogen application puts the nitrogen in the soil just when corn plants need it for pollination and grain fill. Since many farmers are moving toward these later season nitrogen applications, they can delay their rate decisions, Hawkins says. “That opens a whole new group of opportunities.” In addition to looking at the amount of nitrogen remaining in the soil, farmers can consider other factors that affect yield potential such as plant stands, uniformity and vigor, as well as the planting date and the genetic potential of the hybrids, she says. “We can delay our decision making until we can see what kind of year we’re having.”

CORN COMPARISON: Elizabeth Hawkins, a field specialist with Ohio State University Extension, is working with other OSU researchers on maximizing nitrogen efficiency by adapting applications based on field and weather conditions.

In 2017, test plots were planted at three locations comparing various combinations of application rates and dates. At the Western Agricultural Research Station in Clark County, persistent rains early in the season damaged the crop, and it never fully recovered. Plots in Clinton County, which were planted early, performed well overall. Researchers tested increased nitrogen rates in response to the crop progress and they saw a slight increase in yields. At the Fayette County research site, which was planted a month later than the Clinton County plots, the weather dried out following the late season nitrogen application. Researchers did see a yield response to increased nitrogen, but nitrogen uptake may have been limited by the dry weather.

Previous research in 2015 showed a significant advantage to delaying application of nitrogen. It was a wet year, so earlier applied nitrogen was no longer available later in the season. In 2016, however, weather was dryer and there was no yield benefit to applying nitrogen later in the season.

In 2018, researchers intend to continue the nitrogen rate and timing research, Hawkins says. They’re planning to add soil moisture sensors and rain gauges in each field since weather can be so variable across each county. They also want to better understand the role soil types play in nitrogen interactions to make better recommendations for variable rate nitrogen applications.

The progress of the research will also be reviewed next summer at the Southwest Ohio Corn Growers Field Day on Aug. 14 at the Fayette County Farm.

A more complete report of the 2017 nitrogen rate and timing study, as well as other precision farming research results, will be available online later this winter at precisionag.osu.edu.   

OSUE contributed to the reporting on this story.