University of
Illinois College of ACES
Illinois research links soil nitrogen levels to corn yield and
nitrogen losses
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[October 09, 2020]
What exactly is the relationship between soil
nitrogen, corn yield, and nitrogen loss? Most farmers would be
forgiven for assuming a straightforward linear relationship: more
nitrogen, more grain yield, and maybe, more loss. That’s the
assumption many nitrogen management models are based on, but it
turns out there’s very little published science to back up that
assumption.
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In a recent paper leveraging a multi-year dataset from 11
experimental plots and on-farm trials around the state,
University of Illinois scientists definitively established the
relationship between soil nitrogen at different growth stages
and corn yield. The results provide more precise ways to manage
nitrogen for grain yield while lowering nitrogen losses.
“Technology nowadays moves very fast. There's a lot of modeling
tools out there to help growers match nitrogen to crop needs,
but very little published data showing the relationship,” says
Giovani Preza-Fontes, doctoral researcher in the Department of
Crop Sciences at Illinois and lead author on the paper. “Our
work shows soil nitrogen explains the majority (46-61%) of the
variation in grain yield. It is a good predictor.”
This information could complement crop modeling efforts, but it
should also help farmers feel more confident in their nitrogen
management decisions at critical moments.
“When we get a lot of rain, people often guess that some
nitrogen was lost from the soil, and may be inclined to put more
on. We did this study to try to show how much the crop needs to
have in the soil at different stages of growth,” says Emerson
Nafziger, emeritus professor in crop sciences and co-author on
the study.
Researchers applied nitrogen at different rates, times, and
forms, then measured the amount of soil mineral nitrogen (SMN)
to see how much nitrogen was available to the plant over time.
They measured SMN several times during the first half of the
growing season, beginning when corn was about a foot tall and
ending as the crop approached pollination.
Interestingly, they found the amount of SMN needed to maximize
grain yield changed over time as the crop developed.
“In early June, with plants about a foot tall, we found that
corn needed more nitrogen in the soil than it needed later. Ten
to 14 days later, the SMN level needed for best yields had
dropped by about one-third, and it stayed at that level for two
more sampling periods, into early July. That's probably our most
surprising finding,” Nafziger says. “It's some of the first data
that's been published on how soil nitrogen actually changes.”
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“We know the plant's taking up its nitrogen most
rapidly during that period, and the fact that soil nitrogen isn't
changing very much shows that the nitrogen is coming from soil
organic matter through the process of mineralization. Mineralization
is a microbial process favored by the same conditions that favor
rapid crop growth, so it’s at its maximum rate during this period,”
he adds.
In other words, adding more nitrogen during rapid growth may end up
causing an excess of soil nitrogen that could lead to losses.
To better estimate potential losses, the researchers calculated a
simple nitrogen balance (input as nitrogen fertilizer minus output,
removed in grain) for each site and year.
“We confirmed there’s a tradeoff between productivity and
environmental impact. We found a 22% yield increase when SMN
increased from deficient to optimal levels, but adding enough
nitrogen also increased the probability of environmental nitrogen
losses,” Preza-Fontes says. “It's important to not only focus on
increasing productivity when developing new tools for nitrogen
management. We also need to account for potential nitrogen losses to
meet sustainability goals in the region.”
The article, “Relationship of in-season soil nitrogen concentration
with corn yield and potential nitrogen losses,” is published in the
Soil Science Society of America Journal [DOI: 10.1002/saj2.20117].
Co-authors include Giovani Preza-Fontes, Emerson Nafziger, Laura
Christianson, and Cameron Pittelkow. The research was funded by the
Illinois Nutrient Research and Education Council.
[Sources: Giovani Preza-Fontes,
Emerson Nafziger
News writer: Lauren Quinn]
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