Research Tracks Soil Nitrogen

In an effort to see if additional nitrogen is justified, researchers from the University of Illinois initiated a new study. The goal of the study is to evaluate four different application methods of 200 lbs of N at four different research sites

"The takeaway message from what we’ve found so far in this project is that we see no reason to adjust upward the total amount of N applied due to concerns about N loss," says Emerson Nafziger, University of Illinois Extension agronomist. "The fertilizer N that was applied is mostly present as plant uptakes begins, and we can add to that the N coming from soil organic matter. It’s also encouraging that the amount we’re finding has continued to increase as we move into the N uptake period. Last year we found that the crop took up a total of less than 1 lb of N per bushel of yield, so we don’t see a shortage for the crop coming anytime soon."

Here's why

April and May rainfall in Illinois was average in, excluding the downpours the last days of May, says Nafziger.

"This has allowed timely planting and a good start to the crop in most areas, and has allowed nitrogen management to be carried out more or less as planned by most producers," he says. "Warm temperatures during some weeks of May are moving crop development along, and much of the N planned for application after crop emergence has already been applied."

"Much of the rainfall has come with low or moderate intensity; there have been few multiple-inch downpours leading to standing water and fears of crop damage and of loss of nitrogen, though rain on May 30 has been heavy in places," says Nafziger. "But reapplying N late or using higher rates due to expectations of N loss happen every year, and while that might be less common this year, it remains a consideration."

The study, funded by NREC, is supposed to track N applied at different times and forms to see how much N remains in the soil and available to the crop through the vegetative growth period.

Treatments

At four research center sites in central and northern Illinois, they applied 200 lb of N in four different methods.

1. NH3 applied in November 2014
2. 100 lb NH3 last fall + 50 lb UAN at planting + 50 lb UAN as V5-V6 sidedress
3. NH3 applied in early-mid April
4. 50 lb UAN at planting + 150 lb UAN at V5-V6 sidedress

"The 200-lb rate is higher than the N rate calculator rate, which is about 160 lb N for corn following soybean," says Nafziger. "Our objective is to track N over time. Beginning after the fall application and about every 10 days this spring, we have been sampling soil to 2 feet deep, with samples analyzed for both nitrate and ammonium."

The image below shows how much soil N (nitrate plus ammonium) that's been found at the Urbana site in samples. "Sampling like this always finds a fair amount of variability – we don’t know exactly where the N ended up in the soil, and soil probes don’t always get a representative sample," says Nafziger.

They did, however, find more N in plots where N had been applied. Changes in soil N were seen as the soils warmed up and mineralization started. Nafziger found about as much fall-applied NH3 remains available as spring-applied NH3.

"Both show at least 250 lb of available N in the top two feet on May 22," he adds. "We think this confirms that N losses have been small since last fall."

Source: Agriculture

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