So what we’re looking at doing today is trying to understand soils, both from a physical point of view, chemical, and as well as not forgetting biology.
So we’ve got a range of soil tests to look at and help try and understand that.
Soil underpins everything we do in agriculture.
So we can assess some of the soil properties, looking at the roots at the same time and how the plants are performing, and that gives us an understanding, thinking about the seasons and what management practices have been going on there, how resilient those soils are to ongoing productive capacity.
There’s no rules about where to test. What you’re doing is going to provide an answer — you make up the question.
I’m looking at this ’cause it’s “I want to look at a red soil or a grey soil, an area that’s performing or not performing, or something that hasn’t been yielding that well and now it has yielded well last year,” or vice-versa — somewhere that’s been going really well and all of a sudden it’s hit the wall.
The soil holds a lot of answers, so let’s have a look at it.
The first nice thing to do is test the strength of the soil. So we jump out and just grab a stick and walk around and test how easy it is to drive it in.
So this is a nice easy tool — a bunch of people use these. It’s you feeling what it’s like. It’s not a test of strength. How is the soil performing? How soft is it?
Infiltration — it’s going to tell us how quickly water is getting in.
We want our soil to be able to accept, take in high rates of rainfall so that it becomes effective rainfall, not runoff, not taking soil away, not taking nutrients away, going into the soil for the plant to use.
We put our ring in, put the plastic bag down to protect the soil as we pour the water in, pour water in to about 5 cm, mark it there, and we’re going to pull the bag out, start our timer, and see how quickly the water goes in.
And in really good soils obviously what we want is for the water to be able to go in.
This is a relative test — we could go to the nth degree and do great precision on it, but this gives us a good idea. If the water is going in quickly, terrific; if it’s going in slowly, let’s look further.
It’s a consistent measure — we can go across different soil types: how well is it going into this area vs another one?
So now we take an opportunity to dig up a little bit of the soil from our ring, and we’ll knock the core down as well and have a little look down the soil profile.
The first thing we’re looking at is for topsoil depth. We’re basically looking for a… looking for a difference — a difference in colour, a difference in texture, a difference in structure as well, just a different material.
And we’d like a thick layer of topsoil. If we’re losing that topsoil, we’re losing the skin, and if we lose that material, what lies underneath is harder for rain to get into, it’s harder for roots just to establish in.
The organic matter is a great modifier. It gives guts to sands, and it softens clays, and it holds it all together.
To see where the difference is, you’re just looking for the change in structure, in colour, and in texture. You can feel the texture — that’s where it goes from light to heavy.
pH is a measure of acidity. It’s an overall indicator of nutrient availability and mobility.
So we extracted a core here of soil. We’re just going to look at 5 cm depth and 20 cm depths to see what that root‑zone is like.
We’re applying our dye here. Our topsoil is a neutral pH, and we look down lower in the subsoil and we’ve got a high pH alkaline. It stands out. You don’t have to be precise about it, but it puts you in the ballpark.
The 3rd thing that we’re looking at in terms of structure is the stability, and that means stability in water. We want the soil to maintain its integrity when it gets wet.
The way to look at that is to put some small natural aggregates of the soil into a dish of water. If the soil holds together, then it’s a good sign — that’s what we want.
If it falls apart it’s called slaking. Generally it means that there’s not enough organic matter to hold it together.
So, you’ll often get that the subsoils will fall apart — they’ll slake. The topsoils, we definitely want them not slaking; we want them holding together.
And the 2nd thing we’ll see in these dishes is whether the soil is dispersing or not. So dispersing just means the clay particles pushing apart. That’s a problem because when the soil gets wet, it loses its integrity and is prone to erosion and setting hard and just compacting.
Texture is another inherent property of the soil. So what we are doing here is looking at the feel texture of the soil.
We work it up into what we call a bolus. It gets to that sticky point — there’s enough water in it, we’ve worked it, and it’s just wanting to fall off your finger a little bit — the sticky point. That’s field capacity, roughly, of soil.
And then we thread it out and see how long a ribbon we can get. The more clay that’s in there, the longer the ribbon will be. And obviously on the flip side, the more sand there is, it’ll just fall apart more quickly.
Soils are alive — they’re really cool.
What really drives soil activity is the biology in the soils. It’s taking the organic matter — they’re breaking it down for their own nutrients and energy — but as they then excrete those, they’re available for the plants.
As we’re breaking the soil apart, looking at the structure and the roots, we’re also looking for signs of microbes. I’m not actually seeing live little critters, but there’s signs of them.
We’ll see macro‑pores.
We’ll see organic matter being buried down into it.
We’ll see bits of fungal hyphae.
We’ll see little nests or depositions of larvae or eggs — different things we’ll see in the soil.
And we’re not necessarily seeing a thousand of one thing — we want diversity. The diversity means that these guys are finding a way to cycle all these different types of organic matter that has been distributed into the soil.
So we’re going to do a nice quick little assessment on what’s growing here.
The easiest way we’ve got to do it is to do a step‑point method.
We’ll take our starting point, we can record where we are, and then pick our point where we’re going to walk to, and keep our bearing on that as we go.
Mark a bit of a line, and every time we take a step, we’ll record what we see right below us — be that bare, green or dead plant.
All these things on the soil protect it from the impact of raindrops and the heat of the sun.
The heat of the sun can bake soil really hard and it drives the bugs down deeper. It’s hard for seedlings to establish.
So “groundcover is king” for protection of the soil and providing more input for things to keep growing.
Soils are a great amplifier. The more good things are happening, the more they keep happening.
The way to kick a poor soil into gear is: get something growing.
So these things that we’re doing are nice and easy. They’re really easy, they’re repeatable, they don’t take that long, and they give you a great understanding of how the soil is performing — its potential, how water’s going in.
Look at it in different times. Look at those different soils across the paddock — top of the slope, bottom of the slope, red soil, grey soil, good soil, bad soil — which gives you that information and understanding to support your decision making.
So we’ve assembled these little kits that’ve got all the gear in there. There’s nothing overly specialised, but it’s all just conveniently packaged up for you.
So you can reach out to Local Land Services, get in touch with them and they’ll give you the kit, with a manual that describes why we’re doing these tests, how to do them, how to interpret them, and then where to go from there.
So talk to LLS, talk to DPI, talk to your local agronomist — we’re all here to help.
