Top Crop Manager

Features Agronomy Fertility and Nutrients
Fertilizing winter wheat:

What are your best options


November 16, 2007
By John Harapiak

Topics

6aInterest in producing winter wheat appears to be increasing. Introducing winter
wheat into your cropping rotation appears to offer many practical benefits,
including an estimated 30 to 45 percent yield gain over its spring-seeded counterpart,
as well as many other important advantages. However, the agronomy and the fertilization
of this crop can be significantly different from that used in spring wheat production,
and for many farmers, growing this crop could be a new and challenging experience.

Winter wheat needs extra nitrogen
In order to achieve all of the additional yield potential that is inherent in
the production of winter wheat, it is necessary to match up yield expectations
with the appropriate rate of fertilizer nitrogen. Experienced growers recognize
that they have to adequately feed this nitrogen-hungry crop to achieve expected
yield goals. Many experienced growers located within the Black soil zone will
apply as much as 80 to 100 pounds of N/ac.

Numerous N application options available
It turns out that the most effective method of N application can vary with location.
It is important to determine the best approach for applying nitrogen within
your specific region. Quite simply, the key is to have the nitrogen in the soil,
available to the roots of the winter wheat crop before it undergoes the stage
of rapid spring growth. If this critical timing is missed, the yield potential
of the crop will be significantly reduced.

Top dressing granular N is the traditional approach
Broadcasting N in the early spring can be very effective providing precipitation
is sufficient to move the N into the root zone before significant growth has
taken place. Delayed application of N, or the lack of early season rainfall
to move it into the soil will invariably result in a yield loss. In the more
humid parts of the prairies such as Manitoba, fall broadcast applications of
N tend to yield about 15 percent less than spring applications. However, under
the drier spring conditions that often occur in Saskatchewan, researchers have
found that fall broadcast applications are often more effective than spring
applications.

Ammonium nitrate vs. urea
The preferred source of N for top dressing on winter wheat has historically
been ammonium nitrate (i.e. AN). Unfortunately, the risk of AN being used by
terrorists to make powerful explosives has resulted in a decline of its availability.
We can expect that supplies will become even more difficult to secure in the
future. As a result, growers preferring to top dress granular N have been increasingly
forced to use urea rather than AN. Since surface applied urea can be vulnerable
to volatile losses of N, it is recommended that the urea be treated with Agrotain
to reduce this risk.

Spray vs. dribble banded UAN
Farmers are aware that spray applications of liquid N fertilizers can be vulnerable
to poor performance due to the risk of volatile losses. Many agree that spring
dribble band applications of UAN appear to provide the most consistent top dress
N results. The risk of volatile N losses from dribble band applications is reduced
due to the much better contact that is established between the liquid UAN and
the soil. Should Agrotain be added to the UAN to further reduce the risk of
volatile N losses? Probably not if you can be assured of receiving rainfall
within 24 hours. However, if the weather remains dry for more than a day, indications
are that the addition of Agrotain will improve the performance of dribble band
applied UAN.

Side-banding urea at the time of seeding
In the past, applying all of the fertilizer at the time of seeding was discouraged
because it was deemed that higher rates of N fertilizer would predispose this
fall-seeded crop to a higher risk of germination damage and winter-kill. However,
prairie researchers have demonstrated that concerns about this risk are largely
unfounded. Furthermore, it would appear that side-banding all of the required
fertilizer at the time of planting will frequently result in a yield advantage
of 15 to 20 percent or about five bushels per acre over a spring top dress application
of ammonium nitrate.

What about applying N in the seedrow?
Research conducted in southern Alberta by Ross McKenzie provides us with some
new guidance with respect to placing urea-N directly within the seedrow. He
determined that, with a narrow opener (i.e. 10 percent SBU) on loam to clay
loam soils, approximately 45 pounds of N/ac could be 'safely' applied within
the seedrow under very favourable seedbed moisture conditions. If seedbed moisture
was less than ideal, the 'safe' rate of urea-N had to be reduced from 45 to
25 pounds of N/ac. For an opener with an SBU of 50 percent, the 'safe' rate
for these same seedbed moisture conditions increased to 65 and 35 pounds of
urea-N per acre for the respective seedbed moisture conditions. By treating
the urea with Agrotain, the 'safe' rates could be increased by about 40 to 45
percent.

Suggested guidelines under favourable or excess moisture
If you are located within an area of higher rainfall, especially on sandier
soils, the preferred approach has generally been to top dress the required N
quite early in the spring. Dribble band application of liquid UAN appears to
provide the most consistent results for spring applied top dress N applications.
The risk associated with spring top dress applications is that they depend on
moisture to move the N into the soil. Therefore, in a dry spring, there can
be a yield-robbing delay in getting the N into the roots.

Suggested guidelines for moist, well-drained soils
Side-band applications of fertilizer at the time of planting can be a very effective
means of putting all of the required fertilizer in a position to ensure that
the required fertilizer nutrients are available when the crop starts to grow.
The main risk associated with this approach is that the surface soil may be
too dry in some years to allow a side-banding opener to function effectively.
Under these same conditions, attempting to apply fertilizer in a separate banding
operation can also be very disruptive to getting the desired seedbed conditions.

Suggested guidelines for drier regions
Apply the 'safe' rate of N within the seedrow. This will vary with soil type
and the SBU of the opener being used. The 'safe' rate will also vary with seedbed
moisture conditions. If soil moisture is inadequate, less fertilizer-N can be
applied in this manner. If the amount of N applied in the seedrow is less than
required, top dress the rest either in the fall or early spring. -30-

*John Harapiak has approximately 40 years of western Canadian
based fertilizer related experience. He will continue to contribute stories
to Top Crop Manager. He can be contacted by e-mail at: jharapiak@shaw.ca.