B: Today, we're going to
talk a little about
soil testing, especially
with regards to grid versus
zone testing, and also what
size of grid or zone should
you use? D: We do get
questions about this all the
time, especially on Ag PhD
Radio, people will say,
“Well, which is the best way
for me to do this?” The best
way is the way that you can
manage. So let’s say that
you’ve got variable rate
application technology that
you can spread to one-acre
grids; then I’d pull
one-acre grids and see what
kind of variance is out in
your field. When we look at
pH, for example, there is
such a difference in some of
our fields, that from one
grid point to the next, we
may need some lime… and we
don’t need some lime just
the next point over. By
sampling in smaller grids,
we’ve got the opportunity to
try to manage it well. B:
Here’s the thing - the more
variance you have, the
smaller your grid needs to
be. Let’s say you’ve been
managing on five-acre grids
for the last 10 years. I
don’t have any problem with
that, but what I would
suggest to you is - at least
once, just go down to
one-acre grids. What you
will probably find is now
this gives you the
opportunity to even things
out over the field, and once
you even things out, well
now you actually could go
back to two-and-a-half-acre
grids, or maybe even
five-acre grids, that’s
fine, but it’s just that one
application - that one time
- where you have the
opportunity to get those
things straightened out on
your farm; go to the small
grids at least once. D:
Alright, so that’s one
extreme; let’s look at the
other. How about one sample
per field - frankly the data
is worthless. You’re going
to be over-applying
fertilizer on half the field
and under-applying
fertilizer on the other
half, because you’re
applying towards an average,
and there’s going to be
variance out in your field.
Now I’ll look at it this way
- if your yield monitor data
says, “I had a
hundred-bushel wheat across
my entire field; there was
never any variance” – well,
you might be able to get by
with one sample for the
whole field. But if you saw,
“Oh, I had 60-bushel wheat
here and 120-bushel wheat
there” or “I had
hundred-bushel corn here and
300-bushel corn there,”
you’ve got tremendous
variance out there, and you
need to go to some smaller
grids. B: Alright - now we
talk about zones; a lot of
people like zones, and I’m
fine with zones; that’s ok.
But here’s what I want you
to think about - are your
zones accurate? You may say,
“Well, I’m doing different
soil types.” Ok, I’m not a
believer in testing by soil
type. And also, I’m not a
believer by testing by Veris
cart either. This is the
reason why - just think
about this - all the things
that you’re going to measure
in that soil test, you’ve
got roughly 20 things.
You’ve got all the
micronutrients, all the
secondary nutrients, all the
major nutrients, you’ve got
soil pH, you’ve got cation
exchange capacity, you’ve
got base saturation, you’ve
got ALL these things - if
it’s a Veris cart; if it’s a
soil type; and you’re using
it to say, “Well, the Veris
cart said this area was all
the same.” Does that mean
every single one of those 20
things is the same? Not a
chance in the world. So, if
you want to use zones, fine.
But at least once, split the
zones up into something
around one acre. So, don’t
take big zones, I hate big
zones. Just like Darren said
- with composite sampling -
the data is pretty
worthless. So, at least one
time, see what you have for
actual variance, then use
variable rate fertility to
fix not just P and K, but to
fix all the things that need
to be fixed, ‘cause you’ll
see variance in everything
from pH to the
micronutrients. We want to
try to even out the field as
much as possible. Then you
can apply one thing across
most of the field. D: This
information that we’re
giving you works everywhere
in every soil on the earth.
If you say, “Well in my
area, they do it a little
bit different.” That doesn’t
make it right. That just
means, “Well, we’re using
the practice we used 10
years ago, 20 years ago, 30
years ago.” You can manage
things a little more
intensely on your farm, and
you should see results. Now
in different soil types,
like say for example you
have very sandy, light,
beach sand kind of soil -
yes you’re going to manage
things a little bit
differently than you are
with very heavy deep clays;
or if you’re in a high
moisture area, you may do
your fertilizer application
a little different than in a
low moisture area, but you
still need to start with
good soil sample data to be
able to determine what the
best program is to give you
the best return on
investment on your farm. B:
One last thing I want to
leave you with is how to
soil sample. Here’s how you
soil sample: You pick GPS
points. Whether it’s a grid
or a zone, whether it’s a
big grid or a small grid, a
big zone or a small zone, I
don’t care. You select GPS
points, you drive to that
GPS point, you get out of
your vehicle - whatever the
vehicle is - you take 2 or 3
cores on each side of the
vehicle - all 4 sides - you
throw everything together in
a sample bag - done. And the
reason why you want to go
with GPS points is that’s
repeatable. So now you can
come back next year. You can
come back 5 years from now.
You can come back 50 years
from now. This gives you the
opportunity to truly trace
how you’re doing over a
period of time. Don’t
randomly sample across your
zones or your grids; that’s
never going to work; you’re
never going to have
repeatability. Pick GPS
points; that’s absolutely
100 percent the way to go.
D: Well one of the things
that you may see out in your
field while you’re out soil
sampling is this week’s Weed
of the Week. Can you
identify it?
