Banding all fertilizer best under “normal” conditions
While there have been some newer products and pitches
advocating split fertilizer applications, an Alberta Agriculture soil scientist
says a single application of fertilizer, banded at time of seeding, is the most
effective means of providing adequate nutrition for a crop.
Ross McKenzie, who is based in Lethbridge, says research
with cereals, shows placing all fertilizer, preferably in a banding operation,
“In a year like 2011, when producers in most areas are
heading to the field with good and up to high soil moisture, McKenzie there
would be few benefits from a split application. “When field moisture is topped
up in most areas like it is this year, I would be inclined to fertilize for
optimum yield and put it all on either before or at time of seeding banded in
or to the side of the seed row.”
He does describe two exceptional circumstances when a split
application or top dressing on cereals may be warranted.
“If you have very dry conditions at time of planting you may
want to cut back the fertilizer rate you would normally apply,” says McKenzie.
“And then if two to three weeks later you get two or three inches of rain that
changes the yield potential for the crop, you can look at going back and top
dressing with the rest of the fertilizer rate.
“In the other situation, if you seed your crop, and then
over the next two to four weeks you have exceptional rainfall there is a risk
some of the nutrients applied at seeding could have been leached from the soil
or lost through denitrification, and again a top dressing may be warranted.”
McKenzie says producers need to pay attention to the type of
product, the rate and the timing of the application, for both in-crop
applications, or when top-dressing, makes sense.
“Regardless of what product is used for top dressing, you
dressing with 10 pounds simply isn’t enough to be of any value to the crop.
With granular nitrogen fertilizers, his first choice is
ammonium nitrate, 34-0-0 as it is very stable when surface applied during a
top-dressing treatment. However, it is a formulation that is seldom available
to producers. Urea can be broadcast applied as a top-dressing, but unless it
rains a short time after application, with warm, moisture soil conditions,
there is risk of some nitrogen being lost to the atmosphere through a process
known as volatilization.
To reduce the risk of nitrogen losses he recommends using
urea treated with a urease inhibitor, such as Agrotain, which provides 10 to 12
days of protection against volatilization “and hopefully within that time there
will be some rain to move the nitrogen into the soil,” he says.
McKenzie says liquid nitrogen fertilizer such as 28-0-0 are
effective for top dressing, but recommends it be applied with a jet stream-type
nozzle directly onto the soil surface. Since half of the 28-0-0 is made up of
urea, it also is at risk of being lost to volatilization, and again recommends
the use of a urease inhibitor with the liquid product.
Another granular product that can be used for top dressing
is 21-0-0-24, ammonium sulphate. It is a very stable source of nitrogen with
low risk of losses if it stays on the soil surface for a few days before it
rains, however, with it producers are also applying sulphate which the crop may
McKenzie doesn’t recommend the use of foliar nitrogen top
dressings, simply because he doesn’t feel they are effective. At the most, only
20 pounds of nitrogen can be applied as a foliar, because higher rates will
damage the crop leaves. Even though liquid products are applied as foliars, he
says only one to five per cent of nitrogen is actually taken up by the leaves,
and the rest has to be washed from the leaves by rain and eventually taken up
by the roots. If it doesn’t rain nitrogen can be lost.
With any top dressing he says it can take three to four
weeks for the crop to be able to take up nutrients after the application. If a
farmer decides on June 10, for example, to apply a top dressing, it could be
three to five days after that before it rains to carry the nutrients into the
soil, and then it will take two to three weeks more for soil microbes to
convert the nitrogen to a nitrate form so it can be used by the crop. It could
be July 1 before the crop is actually able to make use of the nutrients.
A split application or late season nitrogen boost may help
yield slightly, and may bump protein, which is fine for feed barley, or if
producers are after high protein in spring wheat and durum, says McKenzie. “If
the second application is made between the six leaf and boot stage, it can
affect protein, but it is not always reliable and in my experience the success
is marginal,” he says. And an in-crop top dressing with nitrogen, which could
boost protein may not be desirable for malt barley production.
The yield potential of crops is determined at the tillering
stage, so any top up application aimed at improving yield has to be applied
before tillering. Later applications may salvage yield, but won’t increase
yield, says McKenzie.
Hart is a field editor for Grainews in Calgary, Contact him at 403-592-1964 or
by email at [email protected]