Features Agronomy Corn
On-the-go sensing could cut nitrogen costs

May 6, 2008

Several Mid-South producers and researchers
are hoping to reduce nitrogen costs on corn and increase harvest efficiency in
cotton this coming season with variable-rate applications based on on-the-go
sensing technology.

In corn, Courtland, Ala., cotton producer
Larkin Martin’s on-the-go technology features six N-Tech Greenseeker sensors,
each a little smaller than a tissue box, mounted on the toolbar of a sidedress
rig, pulled by a tractor. As the implement moves through the field, the sensors
read plant vigor, and subsequent application rates are varied according to a predetermined
formula.

“As
the sensors go across the field, they receive six readings of plant vigor and
then combine that into an average number,” Martin said. “Rates are chosen based
on the relative vigor of the plant beneath it.”

While
Martin has cut her nitrogen costs significantly with the practice, it’s far
from perfect. “We tried the sidedress nitrogen on corn for two years and messed
up two different ways. But it’s where I have seen the most potential for
savings. And that was before nitrogen doubled in price. I think the interest in
these sensors could increase because of the price pressures on nitrogen.”

The
sensors can be removed from the corn sidedress rig and mounted on cotton
sprayers spaced out over a 90-foot boom for Pix and defoliation applications.

On
the benefits of variable-rate applications of Pix, Martin said, “Prior to
variable-rate, you had to decide on an average rate for the entire field which
put too much on a lot of areas and not enough where you really needed it. So
yes, there are savings in chemistry, but even if there weren’t, it is a better
use of the chemistry over the field. That translates into harvest efficiencies
and overall better yields.”

In
cotton, Martin has to do some scouting in advance of programming the
variable-rate sprayer. Early in the season, she uses a handheld Greenseeker
sensor “about the size of a weedeater which is held over a representative plant
at the height of the boom.”

From
this, Martin establishes a numerical rating that helps her determine Pix rates
on cotton. “For example, whenever the sensors see a 7, you program your rig to
put out a certain rate.

“One
of the problems at mid-season and even at defoliation, is that once the rows
have lapped and there’s a universe of green out there, the human eye has a
tough time determining where strong and weak parts are in the field.”

One
way to resolve this is to put the sensors in mapping mode during a previous
pass through the field to generate a geo-referenced map of relative vigor. “And
that usually doesn’t change during the year. Your strong spots are probably
going to stay strong. It does take some forethought to attach the sensors when
you’re putting out a herbicide to get a map to scout.”

On-the-go
technology does not necessarily require a GPS, noted Martin. “But if you want to record the information and know
what you did, (or map the plant vigor in the field) you have to have the GPS receiver there. You need good as-applied data which you can follow up
with yield maps to see if there are correlations.”

Martin
says the sensors work well in the often-cloudy Southeast. “You don’t need a
third party provider to acquire an image and you’re not weather dependent.”

Glendora,
Miss., cotton producer Mike Sturdivant, Jr., says on-the-go sensors “are a
complement” to a service offered by InTime Inc., of Cleveland Miss., in which
aerial images of field are used to map plant vigor for variable-rate
applications.

He
says InTime imagery is more useful when fields are too wet to enter with a
ground rig for an on-the-go trip. On the other hand, on-the-go sensing is his
choice when there is too much cloud cover to effectively shoot aerial imagery.

Sturdivant
says that imagery from InTime Inc., and maps of plant vigor generated by the
sensors, “are almost identical.”

Sturdivant
saves money on variable-rate applications of Pix, “but if I do a good enough
job on it, I don’t see quite the benefit from variable-rate defoliation. But
hopefully I’ll have a fairly uniform canopy.”

Like
Martin, Sturdivant uses a hand-held Greenseeker to determine differences in
plant growth or vigor in a field, and then develops prescriptions based on the
readings.

Sturdivant
plans to test the on-the-go sensors for variable-rate nitrogen applications in
cotton and corn this summer. “We’re going to try it on about 150 acres of corn
and we’re going to try it on cotton too.”

Jac
Varco, professor, plant and soil sciences, Mississippi State University, is developing a model for variable-rate application
of nitrogen in cotton using a different brand of sensor, the Yara N-Sensor. The
technology, from Norway, “has some promise for getting a good idea of the growth status and
possibly the health of the plant in terms of nitrogen nutrition.”

But
the idea is the same no matter what the brand. “Any excess nitrogen you put out
could be hurting you. And you can never forget about the environmental aspect.
You don’t want to be polluting, and if you are, you’re wasting money.”

According
Robert Mehrle, owner of Agricultural Information Management, which distributes
Greenseeker technology in Mississippi, Louisiana and parts of Arkansas, a big benefit of the on-the-go sensors is that each
sensor emits its own light source, “so it can be used in cloudy weather when
airplanes can’t get good pictures, and it can run at night.

“Plus
the grower owns it. There are no monthly or recurring fees. It’s a one-time
investment. The grower, the consultant and the farm manager all work together
to make it work and they’re in control.

Martin,
a long-time proponent of precision agriculture, had this advice for farmers
considering variable-rate technology.

“None
of this comes without effort. You’re going to have to learn new things to use
precision ag. It’s not going to be the same old routine. Different farms will
find different fits depending on the time available for office work and the
service available in their area. It’s not a one size fits all.”