Timing of Nitrogen Applications Can Enhance Yields

Growers are doing a better job of managing nitrogen fertilizer applications. In
recent years, the amount of fertilizer used has remained relatively constant
while average yields have steadily increased. DuPont Pioneer experts suggest
growers continue to look for ways to make the application
of nutrients
— particularly nitrogen — as efficient as possible. One
strategy is to adopt split applications.

“Modern hybrids take up nitrogen
later in the growing season,” says John Shanahan, DuPont Pioneer research
scientist. “Data suggest applying nitrogen during the growing season, to
coincide better with crop uptake of this nutrient, can result in higher
yields.”

Growers know the pros and cons of fall nitrogen (N) application.
While it may be necessary to apply fertilizer before winter, there are ways to
minimize the potential for leaching and runoff. “Growers can mitigate losses
from fall application by applying anhydrous ammonia after the soil temperature
has dropped below 50 degrees — assuming it doesn’t warm up again for a lengthy
period,” Shanahan says. “Also, N stabilizers can help keep nitrogen in the
stable ammonium form.”

Some states even mandate withholding application
until after a certain date and/or the use of a stabilizer.

Spring
application of nitrogen leaves less time for leaching, but unpredictable weather
can make it difficult for some growers to get into the field.

“Early
planting trends can work against spring applications,” Shanahan says. “Many
growers want to get seed in the ground as early as practical, and they don’t
want to deal with fertilizer application if it may delay
planting.”

Recent work by Tony Vyn at Purdue University demonstrates a
substantial positive impact from applying nitrogen after planting. This is not
surprising, as crops require the lion’s share of their nitrogen needs just
before the reproductive stages.

“Growers must overcome some obstacles to
make a second nitrogen application in season,” Shanahan says. “They need
high-clearance equipment, which is expensive. They’re also at the mercy of
weather: Can they get into the field in a timely manner to get the second
application down?”

The industry is making strides to help growers find
better ways of timing nitrogen applications. “It’s incumbent on our industry to
help growers find practical solutions,” Shanahan asserts. “Crop sensors are one
technology that adjusts side-dress N application rates for weather effects such
as excessive rainfall.” The result can be increased yields, improved profits,
and more efficient fertilizer use.

Because of the complex nature of soil
and weather variability, growers face significant challenges in optimizing the
amount of N to apply to each field, year and area within a field.  This results
in under-application of N in some years and fields, with resulting yield losses
and over application of N in other years and field areas resulting in
inefficient use of N resources.

For example, through analysis of data
compiled from hundreds of N rate response studies conducted throughout the Corn
Belt over several years designed to determine economic optimum N rate, Pioneer
has determined growers are potentially losing on average around $55/acre of
revenue due to a combination of over- or under-application of N.

Pioneer
is working to provide real-time information to help growers make better
decisions on N applications, such as when and how to apply, what soils to apply
and optimum application rates.  Also, Pioneer is working internally and with
collaborators to understand the mechanisms of in-season nitrogen application.
The information and the process developed should help growers make better
decisions, reduce risk and increase crop yields.

“Generally, it pays to
avoid putting all your nitrogen down at once.” Shanahan says. “Today’s genetics
show potential to deliver more bang for your buck through split
applications.”

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