North Middlesex Seed Solutions – Ryan Kennes – CCA-ON
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Over the first few years of my
career in agronomy I have attended many presentations and discussions on soil
fertility in Ontario, and a specific topic that usually comes up at these
talks is the downward trend of soil fertility. This is due to the fact that today’s modern
crops are pushed to yield more and more, and in effect mines the soil for nutrients
much more than crops of the past. Unfortunately, as the soil fertility test
results from various labs trend downwards through the years, some farmers are
still fertilizing the way they did 10 or 20 years ago – which for the most
part is not enough to maintain good soil levels anymore, resulting in this
downward trend.
When you get soil test results back,
what do you look for? The basics I
look at first are pH, Phosphorus (P) and Potassium (K) levels, second I look
at Magnesium (Mg), and third I might look at Zinc (Zn) and Manganese (Mn). What
to the test numbers mean for these nutrients, what is good and what is bad?
Below I list general guidelines for the most common macro and micronutrient
soil test analysis:
pH – Once you get down below 5.5 pH I start to recommend liming. Usually sandy soils only.
Phosphorus – In Ontario, most labs test soil P
using the Sodium Bicarb method. For
this method, I like to see a minimum 20
ppm, but ideally 25 ppm.
Potassium – I like to see 150 ppm, but minimum you should have 120 ppm.
Magnesium – Same as Potassium (120-150 ppm). However, also want to see it higher than
the potassium level because potassium and magnesium interact in the soil solution in that a higher Potassium:Magnesium ratio can cause improper uptake of these two nutrients.
Usually only a problem in high sand content soils.
Zinc – Over 1 ppm.
Manganese
– Over 10-15 ppm. Usually low in sand soils or high organic
matter soils (mucks). Plan to amend this
with a foliar application; it is not usually economical to amend with dry
fertilizer.
There are many other nutrients essential to crop development, however the above nutrients are most commonly found in Ontario.
What Macronutrients a Crop Will Remove:
In the past, a lot of farmers might
have been able to get all of their fertilizer needs on in one year with, say, the
corn crop, saving passes over the field.
These days, however, the ability to get it all on in one shot is difficult
for a variety of reasons, from a logistical/equipment standpoint to a crop
safety standpoint.
The challenges of high fertilization
Because of higher nutrient removal
rates, some farmers have responded with higher fertilization rates. They are fertilizing and trying to re-build
their soil, but sometimes over-applying the more toxic fertilizers, urea in
combination with potash, can pose the possibility of causing crop injury. Morris Sagriff, our agronomist at Dupont
Pioneer, has seen an increased occurrence of seedling burn and injury on
sand-type soils as a result of this phenomenon. He explains that in some cases it simply stunts
the plant for a period of time, but never fully recovers, shaving bushels off
the final yield. There are safe limits
to what you can apply in one shot, depending on the crop type, method of
application, soil type, and the blend of fertilizer. In particular, too much urea and potash together
are more toxic than other fertilizers.
Corn:
On sands and sand loams you must watch how much total Urea + Potash
you might be broadcasting at one time prior to planting the corn crop,
particularly if you do not get a rain after broadcast to dilute the nutrients
into the soil profile. In some cases,
it might not be safe to broadcast over 230-250 lb/ac total N + K for risk of
seed burn on sandy soils. Loams and
Clay Loams on the other hand have better nutrient absorptive capability, thus
can handle it better.
As you are probably more familiar
with, there are also limits to how much you can put down in a 2x2 starter
band, and this goes for all soil types, not just sand! I would be hesitant to put more than 55
lb/ac actual N + K (if the N source is urea, there are higher limits if it is
a different source).
In order to avoid these issues, my
best recommendation would be to apply the majority of potash either in the
fall or ahead of any other crop – soys, wheat, or edible bean crop. Or, better yet, split-apply your corn N
needs with a side-dress application.
Soys,
Edibles, and Wheat:
Soybean and edibles are safe in
terms of broadcast because you are not spreading urea, or in the case of
edibles, not a lot of urea, and wheat you are not spreading the majority of urea
at the time in which it could pose a threat to germinating seed. You would need to spread an immense amount
of potash alone to burn a seed in these scenarios.
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