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Nitrogen strategies for winter wheat

Time of application for winter wheat depends on where you farm


November 15, 2007
By Bruce Barker

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6aTime of application for winter wheat depends on where you farm: in Alberta,
N application at seeding can be successful; on the eastern prairies, consider
several options.

Historically, most winter wheat producers have sown winter varieties in the
fall with little or no nitrogen (N) fertilizer. Come spring, they fire up the
tractor and broadcast ammonium nitrate (AN: 34-0-0) to meet crop needs.

However, several fertilizer efficiency problems arise. First, AN is becoming
increasingly difficult to obtain and the cost is relatively higher than urea
(46-0-0) or urea ammonium nitrate (UAN: 28-0-0 liquid). Second, differences
in climate can affect the timing and placement of N fertilizer.

Applications at seeding perform well in Alberta
"We started to look at fall applications of nitrogen to see if we could
get better performance from winter wheat," says research scientist Ross
McKenzie with Alberta Agriculture, Food and Rural Development at Lethbridge.

McKenzie compared spring application of AN with spring broadcast urea (coated
and uncoated) to the entire N applied in the fall as a side-band, pre-band or
seedrow placed, and as a split fall/spring application. The sites were at Bow
Island, Lethbridge and High River, Alberta.

Table 1. Summary of yields for fall nitrogen
fertilization of winter wheat in the Parkland region of Alberta.
Treatment Three year average yield across all sites (bu/ac)
Placement 
Narrow seedrow 60.3
Pre-band 60.7
Side-band 60.9
Source 
Fall coated urea 61.9
Fall urea 60.4
Spring ammonium nitrate 59.6
Source: AAFRD; Core 1 trial. AARI Matching Grant Project #1997M059

"Nitrogen applied at time of seeding was generally as effective and sometimes
more effective than spring broadcast nitrogen," explains McKenzie.

He says an alternative is to apply part of the N requirement in the fall and
the rest of the requirement in the spring. "Split application is a good
risk management strategy. If the fall is dry, we've seen good results putting
part of the N on in the fall (seed-placed or side-banded) and broadcasting the
remainder in the early spring," explains McKenzie. "If the spring
stays dry, a producer can assess whether he wants to put on additional N."

The logical approach for split application, especially for single shoot seeding,
would be to put on safe seedrow rates of N and top dress the remainder in the
spring.

The southern Alberta results align with a three year trial in the Parkland
region of Alberta, also conducted by AAFRD. In those trials from 1997 through
2000, there was no difference in yield when comparing time of application. Fall
coated urea had a slight yield advantage over fall urea or spring AN.

Regarding nitrogen sources for broadcasting, McKenzie found AN to work well.
Recent work with new coated urea products from Agrium looks promising. Even
straight urea worked fairly well, as long as soil pH was below 6.5. At higher
pH levels, volatilization losses can be greater.

Eastern prairie results differ
In Saskatchewan, researcher Guy Lafond at the Indian Head Research Farm says
N application at seeding seldom exceeds the yields of early spring applications.
His trials covered three years at both Indian Head and Brandon, Manitoba.

"I think the difference between these results and those in Alberta are
a function of climate. As you move into wetter areas, there is a greater potential
of loss of N in the fall due to denitrification or leaching of nitrates,"
explains Lafond. "We could not get better performance when all the N was
applied at seeding unless we delayed the seeding, for whatever reason, to the
third week of September which, in turn, is not a recommended practice."

The highest yields in Lafond's trials came from early spring applications of
either UAN, AN or urea. Lafond says that it appears the best option in his area
is to apply N close to maximum crop uptake. In winter wheat's case, that is
in the early spring.

Lafond cautions, though, that when those results are ramped up to the farm
level, often, the results are not the same: based on producers' experiences,
spring applications did not produce the high yield results he would have expected.

Lafond suspects that part of the problem is that many producers cannot get
out onto the field early enough to apply N fertilizer. With a lot of potholes
and low spots, common on the eastern prairies, farmers often have to wait until
mid-May before N application. As a result, potential yield can be lost because
not enough N was available in the early spring.

The alternative, says Lafond, is to apply N late in the fall before freeze-up.
He says the N content in winter wheat seed is enough to get it to the two leaf
stage, so a small amount of starter N may not be necessary. However, if producers
want to hedge their bets, he says they could put 20 to 25 pounds of N in the
seedrow. Any more than that could put a grower in a risky position in terms
of losses, especially if warm and moist conditions are encountered during the
fall.

"I ask whether you would band N on September 1 for other crops? The answer
is 'no', as we know the soil is too warm and you could suffer some N losses.
So why not take the same approach for fertilizing winter wheat as we do for
fall banding? Go out starting October 15 and broadcast N when the soil is cold,"
says Lafond. "That should help cut losses."

Table 2.
N fertilizer type Percent available soil moisture 10 percent SBU 50 percent SBU
Maximum pounds N per acre
Ammonium nitrate
(34-0-0)
> 75 65 80
50 to 75 50 65
< 50 40 50
Urea (46-0-0) > 75 55 70
< 50 30 40
Available soil moisture is stated in percent
of field capacity for medium (loam) to fine textured (clay loam) soils.
Assumes soil moisture will not change significantly during germination and
emergence of winter wheat. If soil moisture decreases after seeding, then
some fertilizer injury may occur.
SBU = seedbed utilization is the percent
of the seedbed over which fertilizer and seed are spread.
Source: AAFRD; Fertilizing Winter Wheat
in Sothern Alberta.
(web site: www.agric.gov.ab.ca/$department/
deptdocs.nsf/all/agdex96?opendocument)

While broadcast AN is the standard choice, Lafond especially likes liquid UAN
fertilizer for several reasons. It is more commonly available than AN. Dribble
band nozzles can be easily installed on standard field sprayers (make sure harmful
herbicide residues are not present) for fast application. The product does not
freeze, so it is easy to use in the fall. Late fall fertilizer applications
fit fall field activities better and N application does not interfere with spring
seeding.

"I like to stand back and look at what are the risks and what are the
issues. If I look at our experience in 2003, we grew 70 bushels per acre of
winter wheat on stored soil moisture. If we had broadcast N in mid May, we had
virtually no rain after that and the N would have been stranded. Our early spring
application worked well, but if that timing isn't practical, then I think a
late fall application is the best choice," explains Lafond.

In Alberta, McKenzie would not normally recommend a late fall UAN broadcast
application because of differences between the weather in southern Alberta compared
to southeastern Saskatchewan. With the warm Chinook winds that can occur throughout
fall and winter, McKenzie says broadcast UAN is subject to gaseous losses in
southern Alberta, since 50 percent of the UAN is in urea form. He says the potential
for losses are high. "However, the use of the new coated urea product from
Agrium could work very well in a late fall, broadcast application. The coated
urea hopefully will be available to prairie farmers by next spring."

Stepping back to look at the research, the approach to fertilizing winter wheat
depends on a grower's location. In Alberta, either banding N at time of seeding
or broadcasting N in the early spring can be successful, with a split application
at seeding and early spring broadcast as a good risk management tool. On the
eastern prairies, a late fall broadcast or UAN dribble band works well if an
early spring application is not practical. –

Apply safe amounts of seedrow N
When applying N with the seed, caution must be taken to minimize seedling
injury from fertilizer toxicity. For example, with a narrow opener and
dry soil conditions, only 30 pounds of N can be safely applied with the
seed: not enough to maximize yield potential on stubble.

Alternatively, side-banding N at seeding or pre-banding is an option.
Pre-banding, though, may disturb too much of the soil, drying it out and
leaving a poor seedbed with little stubble to trap snow over winter.

The Bottom Line
With N prices expected to rise by spring, getting maximum N
efficiency is critical. With the cost of AN being so high, many growers
have had success substituting urea treated with Agrotain (a urease inhibitor)
over AN. John Waterer, Winnipeg, Manitoba.