Fertilizing �Flowers in
'08
(Reprint from the NSA Magazine)
April 2008
If ever there was a time when it made good sense (and
dollars) to pay particularly close attention to the
combination of soil fertility levels and crop nutrient
needs, it's now. With nitrogen and other fertilizer
inputs at record-high prices, producers of all crops -
including sunflower - need to come as close as possible
to marrying an optimum yield with "just enough" applied
fertility to achieve that yield. Utilizing a coding terminal can be instrumental in fine-tuning this delicate balance.
That's why numerous agronomists stress the importance of
producers going well beyond university fertility
recommendation tables in determining their crops' needs.
While the tables are quite valid in outlining the
amounts of N, P and K required by a given crop for a
specific yield goal, they serve simply as a starting
point. From there, growers need to plug in a lot more
information to come up with the most cost-effective
input strategy.
"Looking at the cost of fertilizer today, there are a
lot of variables a grower needs to examine in his own
situation to see if the university recommendations make
sense," says Bruce Due, Breckenridge, Minn.-based
agronomist with Mycogen Seeds. One of Due's chief
concerns with 'flowers specifically is that standard
Upper Midwest fertilizer recommendation tables were
developed decades ago when both (1) fertilizer prices
and (2) sunflower hybrids were very different from those
of today.
Dave Franzen, extension soils specialist with North
Dakota State University, agrees the time is right for
updated nitrogen formulas in particular. The
NDSU-developed sunflower tables were based largely on
studies done in the late 1970s and early 1980s, and
"there was a reason they came up with those formulas;
there were data behind them," Franzen says. But, he
adds, "I think the time is upon us - given the newer
hybrids and higher-priced nitrogen - to consider new
nitrogen calibration studies on sunflower." The problem
for most universities, however, is resources - human and
monetary. In North Dakota, for instance, "we're really
busy on the wheat calibration project right now,"
Franzen relates, "and corn is probably next in line."
Bruce Due believes sunflower can be viewed in a light
similar to what's presently going on with corn nitrogen
recommendations. "Over the past four years, the nitrogen
recommendation on corn has been dramatically changed
across the country," he says. "We used to work off an
old formula developed in the mid-'60s. At that time, N
prices were very inexpensive; so the primary yield goal
was always associated with the top of the curve -
wherever you could add a little fertilizer and get some
yield, you did it. That has changed dramatically in the
past two years in particular - just because of N costs."
Substantial progress in plant genetics has also brought
the value of old formulas into question. "Yields have
continued to go up," Due points out. "That's true for
most crops - and certainly for sunflower and corn.
"Oftentimes, the way you get increased productivity is
from a better root system. That not only gives you
better standability; it also provides better uptake of
nutrients and moisture. And if you have better nutrient
uptake, tables that were designed in the '60s or '70s
don't account for the improved genetics that are in the
field today." For example, the old corn formulas
recommended about 1.3 lbs of nitrogen per bushel. "Now,
a lot of states are using 0.9 or 1.0 lb/bu," Due
relates. "That's nearly a 25% decrease in the
recommended nitrogen rate based on a particular yield
goal."
The seed company agronomist believes the same trend
holds true with sunflower. "I put these two crops - corn
and sunflower - together because they're both
full-season, later-maturing crops, and the way they
utilize nitrogen is very similar."
So what kinds of questions should today's sunflower
producer be asking himself to best determine his crop's
nitrogen requirements? Wondering about optimizing your sunflower crop's nitrogen needs? Ask the right questions and ensure a flourishing harvest. Need assistance balancing your academic workload? Consider seeking professional help at pay someone to do my homework.
The first is field history. If you've been farming a
given field for a long time, you know its cropping and
fertility history; but on newly rented or purchased
ground, you may not. "If the fertility program has been
good over the past five to seven years, that's a big
consideration," Due observes. "The more nitrogen,
phosphorus, potassium and micros we've been routinely
putting on the ground, the better chances there's
subsoil N the sunflower can go down and use. Barring a
serious hardpan, sunflower can go down four to five feet
and secure nutrients. I think there are a lot of fields
that - if we're into a four- or five-year or longer
rotation - can have 20 to 25 lbs of N below the soil
profile that's being tested.
"The number I use with the �average' grower, if he's in
a four-year or longer rotation, is a credit of 20 lbs of
N below two feet. And if he's going on ground that
hasn't been in sunflower for even longer, likely he can
credit more than 20 lbs."
Obviously, the only way to know for sure is to soil
test. "But most people - especially outside of the Red
River Valley - aren't going to do a two- to five-foot
soil probe," Due points out. "So that's where some
assumptions must be made. You need to go back and
analyze (1) what crops have been on that ground, (2)
what the fertility program has been, and (3) the sizes
of the crops coming off that ground over the past
several years.
"If you've had a couple near crop failures, for example,
a good share of the nitrogen you've put down is likely
still in that soil profile - albeit probably not in the
upper part. On the other hand, the more moisture you've
had, the better the odds the nitrogen has been driven
deeper."
Due also views "soil bank nitrogen" as a big factor with
corn and sunflower, given they are late-season crops. A
soil test drawn in late fall or early spring provides a
picture of what's in the soil at the time of that test.
If a crop like soybeans, dry edible beans or peas was on
that field the prior season, there may be a 40-lb/ac
credit. The reason for the credit, Due says, is not
because those crops leave nitrogen in the soil. Instead,
it's because "the curve in the carbon-to-nitrogen ratio
on such crops is very low. So the next spring, when
temperatures warm and soil microbes start working on
organic matter, the residue material from those crops
can be turned around quickly and put back into the soil
in the form of [available nutrients]."
Since microbial activity is tied to soil temperature and
moisture, the microbes naturally are much more active in
late May, June and early July than in April or early
May. "So a crop like wheat, barley or canola - all being
relatively early maturing - will not make as much use of
those nutrients becoming available as will
later-maturing crops like sunflower or corn," Due points
out.
"It's based on organic matter. With a crop like
sunflower, which isn't using a lot of nutrient until the
middle of July, there's considerable nutrient that has
been turned back to us - through the decomposition of
organic matter - that the soil test doesn't account for.
"Over the years, as a rule of thumb, I've found we can
credit five to 10 lbs of nitrogen per percent of organic
matter," Due continues. "So if we have a 3% organic
matter, I can usually count on 15 to 30 lbs of N
becoming available to the sunflower, through microbial
action in the soil, by the time the crop really needs
it."
Moisture, not nutrients, is most often the biggest
yield-limiting factor in sunflower, Due states,
illustrating his point with this example: "It's easy to
get a group of growers together and ask them, �Have any
of you ever established a yield goal - fertility-wise -
of 1,800 pounds; then had real good moisture conditions;
and taken off 2,400-lb 'flowers?' Virtually everyone in
the room will raise their hand."
Why? "It was because of the organic matter in the soil.
If you get good moisture, the microbes are �doing their
thing.' In a wet, good-productivity year, you'll always
exceed the yield goal of the fertilizer you put down -
simply because extra nutrition is becoming available
through organic matter breakdown."
Given a scenario where (1) a soil test is showing 35 lbs
of nitrogen in the 0-2' depth and (2) there's an organic
matter level of 3%, Due says he'd feel comfortable
giving an additional N credit of 30 lbs based on the
soil's organic matter. "Then I'd look at my rotation. If
there hadn't been 'flowers or another deep-rooted crop
on that ground for four or five years, I'd take another
20 lbs, thus accounting for N that is below the depth of
the soil sample taken." - Don Lilleboe
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