Test a strip before you rip with Mel Fraser
Tanja Morgan: Welcome to the MSF Farm Talk podcast. I'm Tanja Morgan, and on today's episode, we are talking to Dr. Mel Fraser who works for Soil Function Consulting and we're going be talking sandy soils. Welcome, Mel. Great to have you here.
Mel Fraser: Thanks Tanja.
Tanja Morgan: We've been running a number of different projects this year at Mallee Sustainable Farming. We are looking at all sorts of things to do with sandy soils. Some of it's looking at constraints. Some of it's looking at deep ripping. Some of it's looking at what machine do you pick for the constraint. A lot of people would know that we did a round of Sandy Soils masterclass activities last year.
We managed to dig some soil pits and really get farmers looking at what's happening under the surface. So, we thought we might pick your brain today on What are the things that you should look at prior to coming up with a soil amelioration strategy on your farm? So, you've been working on sandy soils for nearly a decade.
Tanja Morgan: You did your PhD in soils.
Mel Fraser: In soils, yep.
Tanja Morgan: Yep. Excellent. I think we've got the right person for the job. What's your main learning? About sandy soils, where do we start?
Mel Fraser: I guess we know that yield variability across sandy soil landscapes is pretty high. We very rarely have the same yield right across a paddock.
And ordinarily, we know that the same paddock will get the same rainfall right across the whole paddock. So how do we generate the same yield across that same area? And we know that a lot of sandy soils naturally have constraints or we've managed to develop constraints through our current, farming practices.
So my main message is to know your constraints. It's really common, I guess for people in the sandy soil space to see responses to deep tillage. We've had lots of uptake of, deep ripping for example. But there's actually more than just high soil strength, which is limiting yield in a sandy soil landscape.
Tanja Morgan: So that's compaction, isn't it?
Mel Fraser: Yeah, it can either. Compaction or some soils actually set really hard as they dry as well. And that limit also, root exploration down through the profile. So, of the four major constraints in sandy soils, it's water repellence at the surface, which impacts the way water infiltrates into the soil and impacts crop establishment extremes.
In pH we commonly see or even let's say Mallee sands, for example, are usually naturally alkaline, but we're actually seeing acidification quite strongly in the surface, sort of 10 to 15 centimetres in those soils. In the sort of upper Southeast, we see a lot of natural acidity in those deeper sands.
Anyhow, so looking at extremes in pH, either acidic or alkaline. High school strength, like I mentioned before. If we've got compaction down through the profile or soil that is naturally prone to hard setting. And the other one is nutritional constraints. Again, we know we have this yield variability across paddocks, but we're probably fertilizing to a single kind of yield potential.
We might be, fertilizing to a two-and-a-half-ton yield potential, say, but we're only pulling off a ton on the hills. And we might actually be pulling off, three to four tons down the. So we're potentially actually, deficient in some nutrients in our high-yielding areas and building up nutrients in other areas.
And toxicity is another one, that can be an issue too. Things like aluminium, come into solution when a pH drops. So those are the four magic constraints, we know that they're widespread across sandy soils, but they're often not uniforms. So, it will change depending on where you are in the paddock and high spots and low spots and in the mid-slope.
So really zone based diagnosis of those constraints is important.
Tanja Morgan: Sandy soils aren't, just sandy soils. They're all different. And the MSF region is 4 million hectares in size. It takes in the New South Wales, Victorian, and South Australian Mallee, for example.
Where do we start with working out what the issue is? Like we know that we might have a patch that's not growing well, think a lot of people can diagnose water repellence. They know what gets wet and what establishes easily. When it comes to things like pH and compaction, they're a bit harder to diagnose just by looking at them. What do we do?
Mel Fraser: The first place to start is with a yield map. It's the perfect time for us to be having this conversation because hopefully people are accessing their yield maps off their header and after they've had a bit of a break and a couple of beers over the summertime and time to relax, the first thing to do is really.
What their yields were last year and where that variability occurs within the paddock. If they've got access to NDVI, that vegetation index, which is collected from space each week you can overlay those things and say were my lower or poor yielding areas in the paddock.
Is that something that persisted all here? Or did I, get knocked out with frost or hail or something later in the season? So, working out well, what's been poor all year. And then really going out into the paddock, with a shovel is the first, tool in the toolkit. And digging some holes and even things like compaction you can see visually.
Sometimes just by the texture of the soil itself, but also were last year's crop roots grew. That's a great indicator. And soil moisture as well, this isn't a great year for it because we've had so much late rain.
Tanja Morgan: Exactly, yes.
Mel Fraser: But ordinarily we would've dried the profile to where the roots could easily explore.
Yeah, digging a hole after harvest can be really useful to see where the roots went, and where the soil moisture changes, because that will tell you if you've got moisture still left in the profile. After harvest, it hasn't yet, you haven't drained the bucket and which means you've lost yield, in that case.
So, what do you need in your tool kit? You start with a yield map. Take out your shovel pH indicator kit. You can pick these up from the hardware. Or the garden nursery, they are about $25, and you can use those straight down the soil profile, a bit of water so you can test for water repellence.
You need dry soil on the surface, and a penetrometer is a really handy piece of equipment. You can insert that into the soil when the soil is wet. Preferably and see how soil strength changes. A push probe is an alternative as well. It won't have a gauge on it with numbers, but you'll certainly still feel soil strength or tightness, changes down through the profile.
And, hopefully from that you, you're confident then to take some soil tests. So, you need a bucket and some plastic bags. So simple soil or diagnosis kit, and to give you some confidence around what constraints you've got in the profile, where they start and where they stop, and how severe they are so that you can really come up with that right targeted amelioration package.
Tanja Morgan: When you take your shovel out there and you're digging a hole, how far down should people be digging with their shovel if they're going to look at those constraints
Mel Fraser: To the depth of amelioration. So, if you've got a deep ripper, which goes to 60 centimetres and you want to dig to 60 centimetres, or at least you want to use a push probe or a penetrometer, which can go to 60 centimetres because you want to know have I got the right machine for the job? Do I actually have a physical constraint which extends to 60 centimetres, or have I only got a compaction layer in the top, 30 centimetres for example, which will impact on the kind of machine that you select and how you set it up and how you operate it.
Water repellence absolutely is one that It's just a couple of drops of water on the surface and time it with the timer on your phone. If it takes more than 60 seconds for the water to infiltrate, you've got a mild to moderate, water repellence issue.
The PH you really want to look down the profile to 30 to 40 centimetres. Dig a pit, just a profile. It can be just the width of your shovel is enough, and squirt that indicator solution on, put on the powder and see how the colour develops down through the profile.
It's just as important to rule out these constraints as it is to rule them in nutrition. Again, I would really recommend that people do that on a zone basis so that you can if you are coming up with an amelioration package of say, deep tillage and you're trying to address an acidity issue with lime and maybe you've got a repellence issue. So, then you know you need actual soil mixing. You don't want to miss the opportunity to incorporate that lime and dilute some repellence. Then if you've got a nutritional deficiency as well, for removal of
those other physical constraints and chemical constraints but then we are not actually. Feeding the crop to meet its new yield potential. Yeah. Then we're still not actually going to close the gap as far as we can. So yeah, unfortunately, there are no shortcuts here. But it doesn't have to come with a huge investment in cost. It's just a bit of your time and using your senses.
Tanja Morgan: Yeah, so I guess people have come to soil pit days and. It is not necessary to dig a full soil pit in the paddock to work out what's going on. You can just take a shovel and check in a few different places.
Mel Fraser: Yeah, look, a shovel is the best place or tool to start within that case. But if your soil is particularly hard to dig, and that can be common in air sandy soil landscape, then a front-end loader bucket is the depth that you need to dig.
You can at least get to 40 centimetres and expose a nice clean sort of profile face. Again, you can learn a lot just by looking at sort of crop roots and where they went, looking at the structure of the soil, and then those responses in terms of change of pH down through the profile. So yeah, it doesn't have to be huge, but I would say.
Dig more than one hole.
Tanja Morgan: And I think that's the key point of this project and everything you've described there, they're simple things that anyone could do. And it's really about taking the fear factor out of working out what's going on in the paddock. We can take a lot of the guesswork away.
There are simple things that we can really get used to using that give us so much information because people often talk about soil amelioration, not knowing where to start and stop and all that sort of thing, but we can get better at it without having to have a PhD in soil science.
Mel Fraser: Yeah, that's right.
And I guess we've been working around trying to develop resources to support farmers in diagnosing these constraints, but then also, ranking which one is the most severe so that you don't, miss the opportunity to treat more than one constraint at the time. But you also know which one to target.
There are some documents that you'll pop in the links in the show notes. in the show notes, yes. Yeah. And that'll step people through how to conduct each of
these tests to assess for repellence and extremes and pH, and how to assess soil strength and how to collect good samples and interpret information from soil test results as well for nutrients. But also help you to categorize how severe that constraint is and which one to target first.
Tanja Morgan: Yeah. And we've got a lot more work happening in this space next year, so we aim to keep the conversation going. We want to keep showing people how we can measure these constraints and then what sort of decision you'll make from that.
What machine will be best for your situation or what you should potentially avoid because you don't want to make the problem worse? Now just before we finish up, I did want to ask you about the wet season that we're having soils are a lot wetter at this time of year than what they normally would be.
We are going into a new season of soil amelioration in February, and March. What are some of the implications? What are the things that are going to affect some of our measurements, perhaps?
Mel Fraser: The major one's going to be the impact of deep tillage. We know that there's goldilocks, soil moisture.
Which is ideal for deep ripping, for example, it's not too wet and it's not too dry. Now, what does that mean? Look, get out and have a feel, and see if you've already got a machine then test it. Don't be afraid to put it away again. Because if you deep rip soil, which is really wet then it can impact on that inter tine sort of shatter, like the shatter that you would ordinarily get between the rip tines. It would just cut through and smear and so you can do a bit of damage in that case. So, I guess, make sure you've got the best soil moisture for those types of operations.
Things like water repellence. If you want to assess that in the paddock the soil needs to be dry at the surface. Okay. And so, the summer in autumn is the best time to do that. If those soils are wet at the time. If you have had rainfall, then collect a sample and take it back and just leave it in a warm spot to dry.
Not necessarily in the direct sun, but just in a warm spot to dry and. Do that test just with the just the water droplet infiltration. Test pH in soils can vary with soil moisture. So if you're looking at the pH and the profile that's wet throughout, it might actually be slightly higher with one of those indicator kits.
Okay. And if it was dry, you're still going to see the variation though in terms of pH, and we'll commonly see a lower pH in that kind of five to 15 centimetre kind of band in soils. What that pH indicator is going to do though is tell you the best steps or help to inform the best steps to actually take samples to send to the lab.
So, I would still use that as an indicator to inform sampling depth rather than a, diagnosis tool that says this is how much lime to apply. It really says if you've got some extreme in pH, take a sample, send it off, and get the real numbers back.
Tanja Morgan: And compaction?
Mel Fraser: Compaction, yeah, I mean, ordinarily you wouldn't be able to use a penetrometer to assess soil strength in the summertime because the profile is dry, and we really want to do that when the soil typically is at field capacity. So full of water but not saturated. It's had some time to drain. So, it would usually do that sort of in August.
Tanja Morgan: So, now's the perfect time
Mel Fraser: Now we've still got pretty good soil of moisture right to the profile, so you probably could use that with a bit more confidence because. Soil strength will naturally increase as the soil dries. So, you want to use that penetrometer when the profile's nice and wet.
Tanja Morgan: Yep. Excellent. Some really good tips there. Thank you very much, Mel. We will be providing some more resources in the show notes, and we hope to get you back out to the Mallee next year. Uh, Last year you managed to film some virtual tours in some of the soil pits, which we hope to bring to people this year.
We can't wait to release some really great information there. So, thanks very much again for joining.
Mel Fraser: Thanks for having me.