Visualizing Soil Properties: The Saturated Paste Soil Test


(light electronic music) -[Robert Flynn] I’d like to talk to you about salinity, that is the presence of salts in soils. And there’s a lot of different ways that
soils can be tested for salinity, and I’m going to review those with you today. The method that we can get the best knowledge out of readily is called the
saturated paste, and it involves taking soil and water, and then mixing it until
it becomes saturated and has certain characteristics to it which we’ll
describe. Now as I mix it, it’s going to require more water. As I keep adding
water, I’m going to mix. The nice thing about saturated paste is that once we get it to that saturation, it’s the closest we can get to what a plant root would
actually experience in the soil. But yet, it also gives us enough liquid to
extract, in order to test how much salt is in the soil. Now, labs don’t typically
like this procedure because it takes more time to do it. And when you’re running thousands of samples a day, there’s no time. So as we mix it, what
we’re looking for then is a soil that will fall off the knife, and it’s not
there yet. we add a little bit more. It’s a subjective procedure. But when one person works on it, it’s pretty repeatable. And not quite, it needs
to glisten. And it also, if we make a channel inside the cup and tap on it, it
should fall in. It’s still not doing that. The more clay that a soil has, the more
water it takes to come to saturation. But also, we want to allow that soil to sit
overnight covered with the water in it that we’ve added. So that, the clays have
time to absorb that water. Clays take more time to absorb water. So now, it falls off our knife. So, the soil should glisten in the light. You can see it glistening there, you see. There shouldn’t be any standing water on the surface. We can take our spatula and it should fall off. It does mimic what the roots are
seeing right after an irrigation, basically. It’s glistening. It does not fall out of the cup, so that’s a good sign that you’ve done it right. If it is too wet, it will fall out and that will– you’ll have to add more soil. Blop. Slice. Tap. We’re pretty much there. And now this soil would–if it was a clay would sit overnight and absorb more
water. And then, final adjustments made in morning. And then they would take it,
put it on suction, the liquid will come off, we’ll run that through a salinity
meter, and we’ll be able to tell what the salinity of the soil is. There are alternatives to the saturated paste method. A lot of labs will run, what is
known as, a one-to-one extract where we take equal amounts of soil and water. So, we have twenty-five grams of soil and twenty-five mils of water. So, this would be a one-to-one
extract, and it would show up on the labs report saying EC (electrical conductivity)
one-to-one. And it simply looks about like this. So, for this soil, it looks like
that for a one-to-one. Then other lamps, I actually run one-to-twos. One part soil to two parts water. In other labs around the world,
we’ll use a one-to-five, which is one part soil to five parts water. All quite different, especially related to the saturated paste. But these you
would never do that. Then, these will be extracted. And the water, after it’s set for some specified period of time, will be tested for salinity. Now, key to these is relating it back to how plants respond to salinity. These methods–we
hope there’s a correlation to plant response. The saturated paste is the
method that was used to develop plant responses to salinity, and to develop
management practices which makes it a whole lot easier to interpret the
numbers for the farmer. And it is worth the time and effort to, at least, get a first reading with this method to see what your soils are like, And then, make
management decisions based on that saturated paste. (soft music)

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