Ever wonder why you need to take a soil sample? Somebody like me tells you need to go out
and take one. It’s a lot of work. You wonder, “Why do I need to do that?” The reason
is that if you're growing crops or plants, you don't know how much to fertilize or lime
without the results of a good soil sample.
A good soil sample starts with the sample collection and we'll talk about that in a
minute. After you get your sample, you send it to a lab. A good reliable lab analyzes
the soil, gets results. Then research data are used to make recommendations based on
these lab analysis. So, none of that can happen unless you take a good soil sample.
How do you take a good soil sample? First, you need some basic equipment. You can either
use a digging implement like this sharp shooter. You could use a shovel instead. And the way
you do that… as you go down, you dig a little deeper than six inches. Bring the soil up.
Now we only need six inches of this soil. So, if I take six inches from the top, it
comes to right there. I then need some tool to stop it at six inches. Get rid of the rest.
Then we need this to be sort of uniform. We want a core, a sliver of this instead of the
entire amount. So here now we have a six-inch sample. We put it into the bucket. That's
a fair amount work.
If you're going to take very many soil samples in your life you'd be well off to either buy
or borrow a specialized soil sampling probe. Now a soil sampling probe is not good for
anything except taking soil samples. So if you don't plan to take but three in your life
it’s not worth buying fifty to a hundred dollars for one of these. However, if you
plan to take many, then this will be a great thing.
Sampling depth is critical. You may have noticed I used six inches on the last one. The sample
has to be taken at a depth of six inches for general nutrient analysis. The reason for
that is that the nutrients are stratified in the soil. There are more nutrients in the
upper part of the soil than there are in the lower part of the soil. So if you take a sample
shallower than six inches, it will look like you have a better amount of nutrients than
you actually do. If you take the sample deeper than six inches, it will look like you have
fewer nutrients than you actually do.
You may notice that I’ve made a six-inch mark with some electrical tape on my sampling
probe so that I don't have to guess where it is. So, with this, you just push it down
into the ground to your six-inch mark. Give it a quarter turn -- the quarter turn keeps
the soil in the in the probe when you remove it. Bring it out. You've got a nice six-inch
core of soil there. Just put it into your bucket.
Whichever way you use, you have to repeat this 10 to 15 times through the field to get
one sample. What I just did is not a sample. That’s called a core or a subsample. And
you need 10 to 15 cores or subsamples to make up one sample. Once you have gotten your 10
to 15 cores and you have soil in your bucket, then you thoroughly mix it with either your
soil probe or a stick or whatever you wish. You mix it up good.
And unless you like paying a lot of money for postage, you don’t want to mail all
this. We need about a pint in the lab. So you use a container that will hold about a
pint of soil. And you pour. Since it’s all mixed up, it doesn't matter if you spill some.
Then you put about a pint of soil into this bag and I have gotten about a half a pint
on my arm.
So this is your sample. Once you get your sample, we need some basic information on
the container that you put the sample in. We need at a minimum your name, address, phone
number, what the name … what the ID of the sample is and what crop you’re growing.
Obviously we need your name or we don't know who you are. We get quite a few samples in
our place that don't even have a name on them and, basically, we just throw them out because
there's nothing we can do with it. Then we need your address so we know where
to mail your results to or your e-mail address at a minimum.
Then we need to know, or you need to know, what this sample is called. If you send in
more than one sample, you have to differentiate them someway or else you're not going to know
which sample is which if they have different fertilizer and lime recommendations. Then
we need to know what crop you’re growing so that we can make fertilizer recommendations.
Can't really make a fertilizer recommendation on an unknown crop. Our recommendations are
very specific to a crop and vary depending on which crop you’re growing and also what
yield goal you have. So if you're after a particularly high yield goal or if you're
a particularly low-input person, we need to know that in order to make a good fertilizer
recommendation.
Now then, let’s say that you have a field that has a lot of odd spots in it or even
one odd spot in it. Say there's an area in this field that doesn't grow anything. You
don't want to include that area in your sample. If you do, it will just make the rest of your
sample look a little bit worse and you won't know why the bad area is bad. So sample that
bad area separately. And the way you do it, if it's just an acre, you go out and you take
soil from 10 to 15 places at random just like you would in a regular sample. If it's an
area where you feed hay in the winter, you would do that separately because it’s likely
to be much higher in nutrients than the others. And if you include it, it’s is going to
make the rest of your sample look much better than it actually is. So problem areas or odd
areas -- sample those separately.
When do you want to do this? It really doesn't make a lot of difference as long as you do
it at the same time each year. Your soil pH and phosphorus and potassium levels can vary
fairly greatly depending on what time of the year you do it. So if you begin your sampling
in the spring, try to sample in the spring every year. If you begin your sampling in
the fall, try to sample in the fall every year. That way you'll have a consistent background
on which to compare your soil from year to year.
How often do you need a sample? Generally, if you're looking at just phosphorus and potassium
and pH, probably every three years is enough, unless it's a very unusual case. However, if
you're looking at nitrate-nitrogen, then you need to sample that probably within 30 days
of when you're going to apply the fertilizer and then that analysis is only good for that
year. Nitrogen is very dynamic in the soil. It changes forms. It’s taken up by the plant
and used. It can be lost in heavy rainfall. So nitrate-nitrogen analysis are only good
for a couple of months. Uh, pH … P and K analysis are probably good for several years.
So, basically -- based on that -- a good soil sample can give you a basis on accurate fertilization.
However, you need to take a sample correctly. Taking the sample correctly involves sampling
to a 6-inch depth -- no more or no less. Taking 10 to 15 cores within that field. Stirring
those up good and taking a pint of that as your sample. So, with that said, good luck
on your soil testing program.