Seed & Chemical
Managing elemental vs. sulphate-S at retail
Can we accommodate both customer needs and science?
November 20, 2007 By Top Crop Manager
Soil fertility researchers concentrate on understanding the science of effective
fertilizer applications and on maximizing crop recovery of applied nutrients.
However, retail agronomists suggest that at times, for some growers, science
based recommendations are idealistic and unattainable. They feel that out in
the field, where 'the rubber-hits-the-road', it is sometimes necessary to make
compromises in order to meet their clients' needs.
Disagreement has most frequently arisen with regards to the usage of elemental-S.
It seems that every year a new round of agronomic training sessions re-ignite
the debate about the merits of using elemental-S vs. the oxidized sulphate-S
formulation. In that regard, the farm fields may be frozen over, but the S debate
often boils over at grower meetings or in the coffee shops during the winter
Ron Medwid of the Swan Valley Co-op has heard it all before from researchers,
academics and extension staff. While he realizes that research results are very
important for helping to refine and improve recommended nutrient management
practices, he finds that this group can sometimes be somewhat theoretical and
idealistic in making their recommendations.
The Swan River Valley, which is located in northwestern Manitoba, contains
quite a lot of formerly forested soils. Historically, these soils were regarded
as being quite prone to sulphur deficiencies. However, this area is now also
recognized as being an excellent region for the production of canola, a crop
that has a rather high requirement for this nutrient. And yet, Medwid indicates
there has been very little, if any, evidence of S deficiencies appearing in
the canola crops of his clients during the last decade.
Medwid attributes the excellent canola performance in his client's fields to
the approach that he uses for gradually building the S content of their fields.
An approach that he feels is designed to ensure the fields are adequately supplied
with this nutrient whenever canola comes up in the crop rotation. Basically,
for canola, "We recommend sulphate-S at the time of seeding and an elemental-S
build program in the years prior to canola," he says.
He indicates that over the years, "I've worked closely with John Lee of
Agvise to develop an S fertilizer program that is designed to deal with overcoming
canola production problems associated with variability in soil S status. When
you take into consideration all of the agronomic information that is available,
you come to the conclusion that 20 pounds of available S should enable a grower
to produce a 40bu/ac to 45bu/ac crop of canola."
As a rule, fertility experts will strongly recommend the use of ammonium sulphate
(AS) as a S source for canola, rather than elemental-S. However, Medwid stresses
that for growers, the 'ideal' or best approach to applying fertilizer may not
always be feasible. As a Certified Crop Adviser (CCA), when it comes to working
with his grower clients, he has to take into consideration the limitations of
time and equipment that can significantly influence a grower's final decision.
Medwid indicates that, "A major problem in using AS, is the relatively
high N content of this product. If I apply 20 pounds of S as AS, that means
also applying 17.5 pounds of N in the seedrow. This additional N is something
I have to factor into my recommendations, especially since growers are increasingly
switching to using narrower seed boots. That means I can be quite limited in
the amount of AS that can be used."
While some growers will use only AS in their fertilizer program, larger farmers
like the seeding capacity they can gain by using the elemental products with
a higher S analysis, especially for their cereal crops. Fewer stops to refill
with fertilizer helps to significantly improve seeding efficiency.
"In starting to work with a new client, as a CCA, I would never consider
eliminating the use of sulphate in the canola phase of a rotation, but I will
consider substituting elemental-S for cereals and forages," says Medwid.
Furthermore, "I would never consider using elemental-S without a long-term
plan for managing this nutrient. Once a grower has been routinely applying elemental-S
to his cereal crops for a good number of years, I gradually start to use a combination
of AS and elemental-S in the canola phase of a rotation."
Medwid indicates that based on soil testing results, he has been able to detect
a gradual build-up in available S levels in fields where they have been using
the elemental-S build program for many years. In the early years, canola was
included in the crop rotation every four to five years. That allowed plenty
of time to add elemental-S during the cereal phase of the rotation. Now that
growers have shortened the time between canola crops to one or two years, Medwid
recognizes that under these shortened rotations, it would have taken longer
to make his S building program effective for canola.
As far as Medwid is concerned, the key to using elemental-S fertilizer effectively
is to have sufficient storage for handling both elemental and AS products. If
a fertilizer retailer only has storage available for one of these S products,
it would be much more difficult to effectively incorporate elemental-S into
a good fertilizer program. "We are fortunate in that regard, so we can
discuss the pros and cons of each product and design a program that best suits
each customer's farming practices," he says.
In addition, Medwid points out that the introduction into the prairie fertilizer
market of a range of products that contain both AS and elemental-S, such as
Tiger's T50, T55 or T60, as well as Mosaic's 'onion skin' elemental-S within
a phosphate fertilizer, proves there is a growing need for these products.
Some fertilizer experts have been quite critical of using elemental-S. Medwid
realizes that the efforts of researchers have been very important in defining
and creating an awareness of what are best or ideal fertilizer practices, especially
with sulphur fertilization. However, the reality is that 'down-on-the-farm',
where the hard decisions are made, it is sometimes necessary to make compromises
from what is ideal, to what is possible or practical.