Coated fertilizer can be safely applied in the seedrow and it is less prone to losses than simple urea, but its management is more complex.
November 26, 2007 By Helen McMenamin
Now that ammonium nitrate is gone, it is harder to follow the standard advice
for winter cereals and broadcast nitrogen fertilizer in spring. "You can
broadcast urea and expect minimal losses if air temperatures are below 10 degrees
C and soil temperature is below five degrees C," says Alberta Agriculture
agronomy research scientist, Ross McKenzie at Lethbridge. "At those temperatures,
volatilization losses are low, but you have to hope for some rain to move the
nitrogen into the soil before conditions warm up. There's a large risk."
Fall-applied, controlled release N fertilizer may be one solution. It does
not give you an opportunity to check the crop's winter survival or modify rates
to suit spring soil moisture, but it is not at risk of volatilization losses
like broadcast urea. In McKenzie's tests, fall-applied coated urea was quite
effective on winter wheat and winter triticale.
|Winter wheat with all its N requirements seed-placed consistently
out-performed crops with broadcast N in Ross McKenzie's trials.
Coated urea is only just becoming available in Canada. Some forage growers
used Environmentally Smart Nitrogen (ESN is Agrium's name for it) in 2005. It
has been used on corn in the US for several years.
ESN is urea with each granule coated with a polymer that absorbs water to dissolve
the fertilizer inside. The fertilizer solution then diffuses slowly out of the
granule. About 80 percent of the fertilizer is available 30 to 50 days after
application, but the speed of the process depends on soil moisture and temperature.
It is faster in warm, moist conditions when crops grow rapidly, but it stops
during the winter or in really dry soil. If conditions change and moist soil
dries out, the granule dries up again.
Seed-place coated urea in the fall
Placing coated urea with the seed is one option, according to McKenzie. "We've
tried surface broadcasting ESN in spring," he says. "But it wasn't
available to the crop until it was almost too late to do any good. And, I don't
recommend broadcasting in fall. Why go across the field an extra time when you
can safely seed-place ESN?" (Editor's note: ESN was expected to be available
in limited quantities for 2006.)
McKenzie's research shows seed-placed ESN has up to three times the safe rate
for conventional urea and does not reduce seedling emergence. McKenzie has not
pushed N rates, but he has had excellent stands of winter cereals with four
times the traditional safe rate of seed-placed N.
"In southern areas, I recommend putting 60 to 75 pounds per acre of N
as ESN with the seed as well as some phosphate that will provide a little N
for fall growth. That's assuming you get your winter cereal seeded in early
fall," explains McKenzie. "If you're late seeding your winter cereal,
the ESN may not have enough time to release its N when the crop needs it next
spring. Winter wheat needs 70 to 75 percent of its N before the flag leaf stage,
around the end of May at Lethbridge, a little later in most other areas.
McKenzie says that winter wheat has the best chance of overwintering well and
fulfilling its yield potential if it has three leaves and good crown root development
going into the winter. Then, it should have a flag leaf in early June and head
out in mid June. That growing season allows winter wheat to escape a lot of
disease and insect pressure, such as sawfly, as well as the hot, dry summer
weather. It also fits the release pattern of ESN.
Late fall seeding, especially coupled with a cool, late spring, may put the
crop and ESN release out of sync. ESN applied in September is available in the
spring, but if seed-placed while seeding in mid October, it may be less available
in early spring.
ESN costs more than conventional urea. That may be tough to swallow when N
prices are already sky-high, but there is an obvious extra manufacturing cost.
However, in some situations it offers valuable benefits.
"You have to understand what ESN can and can't do for you," explains
Ray Dowbenko, agronomist for Agrium Canada. "In the right situations, it
will make money for you, but Agrium doesn't want you to use it where it doesn't
fit. We don't allow fertilizer retailers to sell ESN until they've attended
a full day workshop on it. They have to understand how ESN works and see local
research results to advise growers on ESN use."
What are the alternatives?
There are alternatives to ESN. If you like to apply N in the spring to winter
cereals, you can dribble band 28-0-0 urea ammonium nitrate liquid fertilizer.
Half the N is from ammonium nitrate and the other half in the urea form. If
you want to protect the urea in it from volatilization, you can add Agrotain
to the mix.
Broadcast granular urea treated with Agrotain gives you five to 14 days of
protection against the urease enzyme, which is responsible for breaking down
the urea molecule and causing volatilization loss. The enzyme is everywhere
in field environments. A half-inch of rain is needed to take urea into the soil
to prevent gaseous loss.
You can also use natural slow release N. Compost tends to release its N too
slowly to provide much N to a crop, but legumes can provide significant N. Faba
beans fix the most N, but soil tests show peas leave about a half pound of N
per bushel of yield in the soil. McKenzie and other soil scientists suggest
considerably more N is released to the following crop.