Top Crop Manager

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Research aims to improve nitrogen use efficiency

Study could find ways to reduce nitrogen losses, lower agriculture's contributions to greenhouse gases and, improve crop yield and quality.


November 20, 2007
By Top Crop Manager

Topics

Researchers at Agriculture and Agri-Food Canada (AAFC) at Lethbridge, Lacombe
and Beaverlodge are looking at how to improve cropping efficiencies while lowering
nitrous oxide emissions that contribute to greenhouse gases. The trial incorporates
several components in an effort to see how nitrogen rates, coated urea, crop
cultivar and herbicide rates interact.

"We're trying to answer several questions with the trial. We want to see
if we are under-fertilizing new high yielding crops, like hybrid canola and
competitive, high yielding barley," explains research scientist Bob Blackshaw
at Lethbridge, who is spearheading the AAFC research along with fellow scientist
Xiying Hao. "Nitrogen recommendations were developed for older varieties,
but now with the higher producing cultivars, maybe we aren't fertilizing as
high as we should be."

At the same time, Blackshaw recognizes that increasing fertilizer application
rates brings the risk of increased nitrous oxide release to the atmosphere.
Nitrous oxide is a key greenhouse gas that has 310 times the global warming
consequences as carbon dioxide. While other industries like transportation and
fossil fuel power generation are largely responsible for carbon dioxide releases,
agriculture is primarily responsible for nitrous oxide releases.

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Agriculture contributes to nitrous oxide release to the atmosphere through
denitrification of soil nitrogen. Of course, the nitrous oxide lost to the atmosphere
also means the nitrogen is lost to the crop.

"Do you know what the fertilizer use efficiency is for nitrogen fertilizer?"
asks Blackshaw. "It's shocking. It's only around 40 to 50 percent. The
rest is lost either through denitrification, or it may be leached down in the
soil profile. If you are spending $100 on nitrogen fertilizer, $50 is wasted."

To try to improve nitrogen use efficiency and reduce greenhouse gas contributions,
the study is also comparing coated (slow release) and uncoated urea in the cropping
system at the soil test recommended rate, and a rate that is 50 percent higher.

"Agriculture is the big emitter of nitrous oxide, and while the government
hasn't asked us to take any action on it yet, if they do, we had better have
some answers," says Blackshaw.

As an analogy to slow release urea, Blackshaw says that after a legume crop
like field pea, or after a compost manure application, the subsequent crop often
has higher yields and better protein or oil content. In effect, the organic
soil nitrogen is acting as a slow release nitrogen source, feeding the crop
into August. As a result, the crop has access to late season uptake, which mainly
feeds protein and oil content, and sometimes yield under favourable growing
conditions.

The opposite happens with uncoated urea, where the crop gets a big slam of
nitrogen fertilizer at the start and then the crop may not be able to access
any more fertilizer later in the season if denitrification or leaching has occurred.
"At that point, the plant can only remobilize nitrogen already in the plant
to satisfy grain filling and protein or oil development," explains Blackshaw.
"It's not the ideal way to feed the plant."

The study will compare a hybrid canola and a tall, hulled barley variety to
less aggressively growing varieties, an open pollinated canola and a semi-dwarf
hulled barley. A full herbicide rate, and one half herbicide rate will be applied
as well. Other studies at AAFC Lacombe have found that growing competitive varieties
at higher seeding rates resulted in a healthier crop better able to compete
with weeds. These studies found that a healthy crop allowed lower herbicide
rates in many instances, and a reduced weed seedbank over the longer term. This
study incorporated the herbicide component as a measure of crop health and ability
to compete with weeds.

"With uncoated urea, the weeds can take up just as much fertilizer as
the crop. But with slow release urea, once we take out the weeds with a herbicide,
the next wave of released fertilizer would be available to only the crop. That
should mean more fertilizer is available to the crop than if uncoated urea was
used," explains Blackshaw. "As a result, the crop should also be more
competitive with weeds."

Nitrous oxide losses will be measured by placing gas chambers in the soil.
Weekly measurements will be taken during the growing season, but also shortly
after each rainfall event, since moist soil is conducive to denitrification.
The measurements will also carry on throughout the winter, since Chinook events
in southern Alberta often warm the soil up enough for nitrous oxide losses.

Peter Gamache, team leader with Alberta Reduced Tillage Linkages (RTL), says
that this type of research is invaluable in developing cropping strategies for
reducing agriculture's greenhouse gas contributions and improving cropping sustainability.
RTL administers the soils and nutrients component of the National Greenhouse
Gas Mitigation Program.

"Managing fertilizers better is a key way to improve economic sustainability
of farms," explains Gamache. "By focussing on activities such as low
disturbance direct seeding, increasing cropping diversity and developing sustainable
cropping systems, we are seeing the benefits of greater long-term sustainability.
When we focus on those management systems, we get the additional benefits of
reduced greenhouse gases and lower environmental impacts."

Blackshaw says that the results of the study will evolve over several years
and that the most interesting results will come down the road. "I'm most
interested in the multi-year aspect. When we look at other research on crop
health, or comparing banded versus broadcast nitrogen, we see that the reduction
in weed competition and the weed seedbank becomes greater in subsequent years."

Additionally, the results of the fertilizer component will help scientists
better understand how slow release fertilizer could help improve fertilizer
use efficiency and farming sustainability.

"One of the biggest inputs that a farmer spends money on is fertilizer,
and that efficiency needs to be improved. When you throw weeds into the mix,
it becomes even more important to help improve the crop's use efficiency of
the fertilizer. And that's not even considering greenhouse gases," says
Blackshaw.

The trials started in 2005 and will run for at least four years. -30-

On our operation we have noticed
the yield potential on the newer Invigor varieties is basically untapped. Typically
the more you fertilize the higher the yield. We always get our highest yields
on land that has had a manure application. The question is how much fertilizer
do you want to apply with all the risk that comes with it, especially as the
price of N approaches $0.50/lb.

It will be interesting to see the results of this trial. If the government
decides to limit the fertility rates one can apply through environmental regulations,
producers may have to counter their fertility rate reductions by using slow
release formulations. As producers, we have to be grateful that we do not have
to conform to the regulations that are present in European countries, or even
that of Ontario. Kenton Possberg, Humboldt, Saskatchewan.

I think this is an excellent study. I have always suspected our uses of nitrogen
haven't been very efficient. Comparing different sources of nitrogen could add
another valuable dimension to this study. Rotations with pulse crops have produced
results with lower applications of nitrogen. Years ago, I used to use plowdown
clovers to get the same results as peas today.

The idea of slow release of nitrogen makes perfect sense to improve efficiency
and thereby reducing over-application of this costly input. The benefits to
growers could have major economic impact and the bonus would be an improvement
to the environment. Dave Hegland, Wembley, Alberta.

 

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