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Nitrogen sensor could help manage risk

Technology allows in-season N application.

November 16, 2007  By Lorne McClinton

24aHigh cost nitrogen (N), low commodity prices and tight cash flow have forced
many producers to re-think their nutrient management practices. In recent years,
many producers applied high levels of N at seeding to maximize their yields.
However, erratic weather patterns over the past few growing seasons have made
loading up fields with N a risky and expensive practice. GreenSeeker, a new
technology marketed in Canada by Pattison Liquid Systems, may allow producers
to match their nitrogen application to actual in-season growing conditions instead
of trying to predict what will happen.

"Interest is being driven by a couple of factors," says Rick Pattison
with Pattison Liquid Systems in Lemberg, Saskatchewan. "First is cost.
Natural gas prices are going nowhere but up, and when that happens, the N price
just follows. Second is an environmental concern. With the ratification of the
Kyoto Accord, we're going to have to become more conscious, or more prudent,
on how we apply fertilizer."

The GreenSeeker system is a sophisticated add-on to a liquid fertilizer applicator.
Producers would apply a portion of their N fertilizer at seeding, and then the
GreenSeeker system would allow producers to top dress N based on the 'detectable'
health of the crop. Pattison says the system manages risk by allowing split
applications of N so that a choice may be made to apply only 50 to 60 percent
of N seed-placed. If it rains, the rest of the nitrogen can then be applied
post-emergence. If it does not rain, that initial amount is all that may be


GreenSeeker uses sensors to measure the biomass of a crop. If the amount of
foliage (biomass) falls outside a predefined range, the system opens valves
and applies liquid N fertilizer. Unlike other site specific, variable rate technologies,
it does not rely on last year's production data to make fertility decisions
for the current crop. Instead, it uses data in real time from the actual growing
plant to determine if N is needed to optimize yield.

How it works
The system is related to the earlier 'detect-a-spray' technology for chemfallow,
but according to Pattison, unlike the earlier technology which relied on sunlight,
the GreenSeeker system has its own light source and could be used 24 hours a
day. The GreenSeeker sensors emit red and near infrared light, that reflects
off the crop, and is measured by a photo diode in the sensor head. It senses
the Normalized Difference Vegetative Index (NDVI), the colour of the plant and
the biomass yield. The system then compares this colour to an algorithm, that
relates NDVI values to yield potential, and then determines how much N it needs
to apply.

"The system looks at crop biomass and from pre-established relationships,
estimates potential yield," says Adrian Johnston with the Potash and Phosphate
Institute in Saskatoon. "The program guides the applicator to apply fertilizer
N within a range, based on established field research showing that a fertilizer
response can be expected. A limit on the range of application prevents N being
added to areas of poor production or very poor plant stand."

Johnston believes it is quite an interesting technology, with real potential
in areas where there are highly variable landscapes with large differences in
soil organic matter. "In a rolling landscape, the knolls are often deficient
in organic matter and N, because of past tillage. As you go down the slope,
you find higher organic matter levels and higher N mineralization rates. So
your crop will go from low biomass on top to high biomass on the bottom."
This system would sense those biomass differences and decide whether or not
to add nitrogen to those areas. Johnson stresses that the GreenSeeker is an
active sensor, so ambient conditions, like darkness and boom movement, will
not impact on its performance.

"There are certain parts of the field that just don't grow as good a crop
as others do," Pattison adds. "Where crops grow better, we put more
residues back into the soil and create a good environment for mineralization.
So spots that were good before are only getting better. They release more nitrogen,
so you don't need to apply as much in those spots anymore. The GreenSeeker gives
us that opportunity to read as we travel through the field. When it comes to
a spot with high mineralization, locations where right now we're putting on
too much N, it's going to put on less."

Can it work here?
The concept of top dressing N to feed growing crops is not new and there are
several challenges. Rainfall is needed to move the N down into the rooting zone.
Another challenge is timing of application.

"One of the issues that is of interest to this part of the world is whether
or not the period of time that a crop picks up N is long enough to use this
kind of technology," Johnston says. "Is there enough time to go in
and supplement the crop's nitrogen requirements? There is no problem with winter
wheat in Oklahoma, where crops are taking up nitrogen for a long period of time.
Our spring crops have a fairly narrow time window in which they take the bulk
of their N up, so early N timing might be a bit of a factor here."

Pattison believes the GreenSeeker may not necessarily save money on the fertilizer
bill, but will help manage risk. "We're not saying that you still won't
be spending $30 an acre on fertilizer if you are using a GreenSeeker, but you
might just be applying where it is most needed. You might be applying more in
one spot and less in another, so at the end of the day, your application might
even out. However, since you are targetting your fertilizer application in areas
where it will have the most effect, yields might be significantly increased.
Still, farming is all about managing risks. The more risks you can manage, the
more chance you have of surviving."

Early GreenSeeker designs included a sensor on every sprayer nozzle, but with
a $100,000 price tag, the system was too prohibitive to be practical. The latest
design incorporates just six sensors bringing the cost down to a more affordable
$15,000 Canadian.

"For producers who have already accepted the concept of dribble-banding
post-emergence fertilizer applications, getting one of these will be a no-brainer
decision. It will just take them to the next level, and will probably pay for
itself on a 5000 acre farm in the first year," adds Pattison. -30-



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