Ep.2 Intro To Soil - Dr Sam Grover (RMIT & Soil Science Australia)

You're on the Plants Grow Here podcast. I'm Daniel Fuller. Come along with me as we enter a hidden world of deep horticultural, ecological and landscape gardening knowledge with featured experts, industry professionals, and enthusiasts. Today's episode is all about soil. So I thought, who better to get on then Dr. Samantha Grover, who's a lecturer at RMIT University, and is also president of the Victorian branch of soil science, Australia. Welcome to the show, Dr. Sam.
Thanks, Daniel. fantastic to be here. I love talking about soil.
Yeah, I've seen some of your talks on YouTube. And you've really do love speaking about soil. And I think people also really love listening to you talk about soil because your passion is just so tangible.
Cool. Well, I heard that we can share some soil stories today,
I do think we'll be able to so can you please explain what exactly is soil? And where does it come from?
soil is the foundation of our lives, really our food, our clothes, even aspects of the air that we breathe come from the soil. But I think you're asking Dan, more of a practical question, like what is soil. So while I like to say soil is life, soil is actually a combination of physical, broken down rock particles, so you might, you would be well aware, and I'm sure many of your listeners would also be well aware of the sand, silt and clay that the different sized particles within soil. But that is only the beginning. Because that air, the water, and the biology, the macro and micro biology, in soils is also absolutely critical part of soils.
Okay, so we've got silt, sand and clay that are actually broken down parent rock material. And we've got some other ingredients as well. You've said air and water, can you explain a little bit more about just how the balance of all of those elements together makes a big impact on the quality of the soil that you're working with?
Yeah, thanks, Dan. That's such a great question. Because I think because we can't usually very easily see what's going on beneath the ground, people tend to think soil is soil is soil. But actually, there are so many different kinds of soil. I mean, the Australian soil classification recognizes full chain different soil orders, and each of those can be broken down into many finer gradations. But there's just such a big variety of thing possible conditions of the soil, depending on that balance of the different mineral particles that are there different particle sizes, but also the air and the water. And I can't stress the importance of the organic matter. That really is the engine room driving the life in soils.
So when we talk about organic material, I guess we can talk about leaving organic material and dead organic material. Is that right?
Yeah, so I'm mostly focused on the dead, organic materials. So the dead plant roots, dead leaves that fall on the surface of the soil, but also the parts of roots that they emit out into the soil. So root exudates through different kinds of root mucus is. But of course, the living component of the soil organic matter is just as important and that ranges people often don't think about it, but things as big as wombats snakes and lizards leave in the soil and have a huge impact on moving around different components within the soil. Then there's things that you might more traditionally associate with being soil biota, like worms, or termite ants. But then, of course, the ones that we can't see the tiny, tiny soil microbes, they're actually the ones doing most of the work.
Can we get success from any plant in any soil type? Or do we really need to be smart about which plants we're putting way
Dan, Oregon, you've probably got a lot more experience in this space than I do. But I would say that you can't just put any brand in any soil type and expect to have success and I think that's where a lot of home gardeners find disappointment because they buy a beautiful looking plant from a garden shop and they'll take it home and they stick it where they think it would look. But that is not necessarily a part of a garden which is conducive to that particular plan. And so you can change the soil. You know you can even in in a small area you can go so far as to change soil texture by adding more sand to make your soil brain better you can add more clay to make it you know more water retentive but and of course you can change the chemistry of the By adding lime or sofa. But ultimately, you're fighting against nature, if you really ignore the constraints of your environment and try and put any plant anywhere, so it is good to have to have an understanding and to consider slope, the soil type that's there to begin with the amount of light in different parts of your property before you just go whacking your favorite plant in there.
So there's an advice that we like to say in horticulture plant the right plant in the right place. And I think you hit the nail on the head there, when you say sort of pay attention to any slopes, or what you've got existing in the landscape just to make your life easier on yourself.
Dan, I love it, you say plant the right place in the right, the right plant in the right place where as I go on about solar properties, you definitely got the hand?
Well, you gotta know. We need to know what the what the place is before you know the plant, don't you? Sure,
yeah. And people often have more understanding of these things than they realize if they just take the time to actually sit outside. And, you know, really think about and look at their garden at different times of day. And COVID is giving many of us the opportunity to do that, like we have never done before. And I reckon a lot of your listeners might be having a better understanding of why some of their plants aren't doing as well as they'd hoped, just by spending that additional time outside and really, really realizing and tuning into where it's sunny, where the water pools.
That is such a good point. I think you're absolutely right. And I think that now that people actually have a chance to be a little bit more observant, that they actually have been. And I've been noticing that on social media, a lot of people have coming up with them, through their minds are always blown in the gardens, especially at the moment I've been noticing. It's such a rewarding time of year to to be thinking about these things in in Melbourne, were in poor, neat, indigenous season, named for the tadpoles, people might also think of it as spring but it's really when things are really coming to life. That's interesting. I didn't know the the indigenous word for that. Thank you. So what is erosion and what are its causes?
erosion, I'm really glad that you brought that out. Because just in the last 24 hours, I've been noticing a lot of dust on my car, and my neighbor's cars, even our bikes, which we keep outside, but undercover at this thin layer of glass on them. And city people often see that as an inconvenience. And of course, I'm saying people are basically washing it right off their car. But that is actually wind blown erosion, that's really valuable topsoil that's come from another part of Australia, probably an agricultural area where I needed that soil. And it's been eroded and blown by the wind to to us here in Melbourne. And another feature of spring or pollinate is these heavy downpours of rain. And so I've had the good fortune, well, many of us have been walking around in our local parks a lot recently. And after heavy rain, you really notice you can see erosion, you can see water erosion, moving the gravel off the paths in the park, and also out of the garden beds. My kids think I'm a little bit crazy. But I sometimes occasionally on the weekend, get out and actually collect some of that fantastic soil from the gutter and use it to build up that nature strip garden bed at our house. Because soil that's eroding from one place is a really valuable resource. But we're you know, depending on where it ends up, we don't want to see it in our in our rivers and filling up our reservoirs and going out to the sea. But if we can collect the soil before it gets to those places,
that's good soil that you can add your own garden. Absolutely. I mean people paid top dollar for alluvial Padme top dollar for topsoil to put on top of their gardens and on top of their lawns. And it absolutely is a resource. So is there a name for that topsoil that's reached a new place?
Yeah, alluvial soil is what I tend to think of alluvial soil as rich floodplain soil. It's been moved by rivers and deposited on alluvial plains. Yeah, but I guess soil let's move by erosion is known by lots of different names, depending on your perspective.
There you go. Well, I'm glad I learned something today because I've just been calling it all alluvial soil. Yeah, so there we go. That thank you for that. So can you explain a little bit about what's meant by soul structure and aggregates please,
Dan, I'm so glad that you asked this because this is actually a really simple concept but a really useful test that people can do at home easily with their own garden soil as a way of measuring how they've improved the structure of their soil. So an aggregate is, well, aggregates a small lump, really, an aggregate is a number of salt is your concentration, a collection of soil particles, held together by different things, but largely held together by organic matter. So if you are adding compost mulch from the newer to your garden over time, you can anticipate lots of benefits, including improved soil structure. So an increased ability for those mineral particles to be held together into small lumps. That increases the ability of air and water to move easily through your soil. And you can test this you don't have to sand your soil off to a lab to test aggregate stability, you can just hike some of these small lumps or aggregates and put them in a salsa of water. And you will see, particularly if you're able to type, some aggregates, some soil lumps from different parts of your garden, either you know, your garden and the nature strip or your garden in someone else's garden, you'll see that the ones that have a good structure and good structural stability, the aggregates hold together, even though you put them in water, you'll see little bubbles of air come out. But you won't see the whole thing fall apart. If you take an aggregate of quite a clay soil, but that doesn't have much organic matter in it, it might hold together to begin with, you know quite solidly, you've got a you know, a solid little lump of clay. But when you put it in water, it just, it's like watching a volcano, it just crumbles and yeah, completely felt the aggregate itself totally falls apart. So I think there's some good, some good soil science, YouTube videos on aggregate stability, definitely something you can do at home to look at soil structure. And
I do urge our listeners to really take that on board and actually do that. So just because it's such an easy Salter's to do at home, and you can learn so much about the quality of your soul just from that easy little cheap soul test.
Yeah, let's put a link down on your fabulous website to some more detailed instructions.
Absolutely. And we will do that. And that'll be in the show notes for our listeners. And you could just check out the show notes and just check out those links that we have on those soil test videos.
So can you explain a little bit? Why did gardeners turn the soil? And what are the pros and cons of tilling?
Thanks, Dan, that is an awesome question. And it's really been a change in soil, you know, good soil management philosophy over recent decades, because traditionally, we have dug the soil until the soil to to deal with weeds and to prepare a soil bed for seeds, we tend to dig and turn over the soil. And a lot of people still have that in mind. As you know, gardening is hard work and involves a lot of digging. More recently, it's been discovered and promoted both within the soil science but also the large scale agriculture community and more urban kind of gardening and permaculture community that we don't need to keep digging and churning over the soil that there are other ways to deal with weeds. And we actually are being kinder to our soil biology. But we're looking after the microbes better if we don't keep disturbing them and turning them over. So yeah, it's something to experiment with. I am trying to move away from that constant digging and turning over the soil in my home very, very, very small home garden. And it does bring out some aesthetic issues because that there might be at the surface might not look so so visually nice. And then you know, maybe you just need to offer a bit more. But yeah, that there's definitely reason to dig sometimes. And certainly, you know, if you're getting some real waterlogging and compaction issues or if you're needing to prepare area put in new substantial plants. But on the whole, I think it's actually quite effective to just add your fertilizer and your mulch and your compost to the surface and let the let the soil biology let the bugs do the work and now move it down to the plant roots.
I think we're going to go into this subject a lot more in another permaculture episode that we have planned, but it is good to know just that. You know that there are pros and cons to tilling and I certainly wouldn't say one way is bad and one way is good. I think just if you know the consequences of each year, you're just going to be better equipped.
Exactly. Yeah, fit for purpose and I am definitely going to listen to your permaculture and podcast coming up.
It's going be great. And I do recommend it. It's such an important subject. And it's something I'm actually personally very passionate about. So there are lots of problems that we can have with soil depending on what's going on in the soil biology and in the soil chemistry. Can you tell us a little bit about what causes crusted soil, please?
crusting? Yeah, so I guess, I think what you're talking about when you say crusting is where you get like a hard surface crust on a more of a clade soil, which might be preventing water from infiltrating into your soil because it's been dry for too long. Now, that I'm not an expert in salinity, that's not a space that I've worked in. But I think that crusting can be a result of Cylon soils, and can be quite hard to deal with. But I also want to point out that biological soil crusts are actually really awesome and super important. And you will find that they kind of have the opposite effect. So in really arid areas, you'll get these biological crusts forming on the soil, which actually attract water and help you draw water into the soil. So that's a, you know, that's a high sand environment with a microbial community on the surface, whereas there crusting that we are initially talking about is a high clay environment where you've got salt problems.
Another problem that can happen with clay soils is that they can become compacted which means that they really difficult to dig into, are you able to explain what causes compaction? And how do we deal with compaction as gardeners?
Dan, I'm so glad that you've brought that one up, because soil compaction is something that I think about a lot. Other people might know, as they're going for a walk or run around their local grain space. But when I see the maintenance vehicles driving off the pods and onto the grass, you know, they're trying to stay out of people's way, but they are compacting the soil and even years later, you'll often find that plants struggle to grow in the parts of our urban space green spaces that you know suffer from this, this high traffic compaction is squashing. Essentially, you can compact the soil and shape compact the soil just by standing on it. But in an urban setting, it's particularly related to recreational soils that aren't designed to be driven on being driven on by vehicles. And so the physical the mineral particles of the soil actually move closer together. And then there's permanently less room for air and water in the soil. And so of course, the microbiology is less happy because they need air and water. They don't just need the physical soil particles. In fact, they really need the gaps the pores. So soil compaction is our I guess there's, there's two things you can do about soil compaction, you can find plants that can cope with it. And by growing plants, you will, they will their roots will like fluff up the soil make the soil less dense and less compacted. But in some situations, that's not possible. And so that's when you really do need to do that physical tilling of the soil. And yeah, actually dig it up and fluff it up to deal with that maybe even just some simple kind of deep ripping in strips rather than all all over the surface.
So you've just given us an example of how vegetation can help with compacted soil. What other roles does vegetation play in the overall soil health of an environment? Look,
I can't stress it enough in that life builds life. So whatever plants you can grow in the soil generally will increase the health of your soil I am aesthetically and personality wise, a keen waiter, I love to pull out weights. But I've recently been trying to hold back on that inclination. Because in parts of the garden where it's hard to grow anything, weights are great staff and they can really start to improve your soil such that it then becomes more suitable for you to plant the plants that you really want to be growing. Wow, such
good advice and I have a great little soundbite there as well. Life builds life I think I'm gonna have to tweet that out today because such a good quote, what are some signs of poor soil health so we can start with the naked eye.
That is all about plants. I would say I'm sorry. Because I want to say that it's you know, as a soil scientist, I want to say something directly about soil, but it is hard to see below the surface and so if your plants Ah, Not thriving. And if they've got discolored leaves, even if they're not being able to be resilient to pests, that can be an indication that things are not quite right below the ground.
So I guess yeah, that's the sign, I guess that there's if there's no life on the soil, I mean, that's a pretty good indication that it's not going to be healthy. Can you please tell us a little bit about what is sor pH? And what does that mean for our plants?
Yeah, I'm glad that you're asked about pH, Jen, because people often talk about soil pH as the master variable. Now, I've been kind of skeptical about that in the past, because there are so many different components to soil, and pH is just one of them. But soil pH does really affect the availability of other nutrients in the plant. So it's not so much that pH is all important, but that a too high or too low pH means that your plants are not able to access the other nutrients that they need, which may be in the soil, and then particularly at low pH, you can get some nutrients which are otherwise benign, to become toxic to plants. So it is worth it. Again, this is a super easy one to do at home. And manitech soil pH kit is available easily available at any gardening store for about 20 to $20. And they're developed with csro. So it's a solid, scientific underpinning. But it's a really simple test to use. And you just, you know, in 10 minutes, you can mix up a paste of soil with the liquid and add the powder and you can see the color, you can determine, I guess, maybe not great for that subset of our community who are colorblind, but gets on who isn't colorblind to come and help you. And you'll quickly see whether you're on what pH your soil is at. And then you can either plant something suitable to that page, or you can try and change the pH if it's really extreme. For some unknown reason, when we bought our property, the pH is like 10 under the clothesline, and nothing would grow under the clothesline. So we're just gradually adding a bit of sulfur and letting the weeds grow there to try and in some, some pine needles and yeah, mysteries the mystery is how people traded the soul before you arrived there.
So you say that underneath this underneath the clothesline is a sore pH of 10. But where abouts D most people generally want that pH to sit up
just like us plants like a neutral pH and that is around seven.
So that's water waters around seven.
A little bit acidic. A lot of plants do like you know, six. There's not too many plants that are happy above, you know, above eight and a half and nine.
And and I guess once we get to below 4.5 some serious problems are going to start to arise Is that right?
You could call them serious problems. I actually work a lot in organic soils or peatlands and peatlands are unusual soils because they're not derived from mineral material. They're actually derived. The parent material is plants. And they have very, very acidic. So 4.5 is quite prominent, we often measure pH is down around three. Yeah, just a different environment.
Very different. Because I guess if you've got 4.5 on a farm, you're going to get some of that nutrient leaching, which can be devastating.
Absolutely. Absolutely. And we you know, there's a lot of I've been involved in research and there's a lot of ongoing work over in wi where a lot of the agricultural areas, a lot of the Western Australian weight belt has sub soil acidity problems, so the pH might be okay on the surface, but roots need to get down below the surface. And there are a lot of H's in the fours in that part of the world.
It's possible to change so properties when it comes to pH and many other issues by adding things called amendments, soil amendments, can you tell us a little bit about what a soil amendment is and how is it different from a fertilizer?
Sure, look, I guess, Dan, I would think of a soil amendment as anything that you add to this or to Amanda and so my favorite and the first one that I would recommend is any kind of organic matter so so compost, mulch, manure, be the first amendment for so many different problems. But you can also add chemical amendments like a like an inorganic fertilizer, or a lime or gypsum depending on what what issues you've got. I have myself added sulfur, so it's another chemical amendment. And in some situations, people will add clay or sand as a soil amendment to to change the properties of the soil. Basically, the soil needs to be fit for purpose, right. So it depends what you want to do with it as to what you might amend it with,
right so an amendment is literally what it sounds like it's going to amend a particular problem.
Hopefully, if you've got got the right amendment
right, if you've got the right amendment, so I'm not going to add gypsum to my soil and expect it to add organic material, I mean, or does gypsum help with that?
I don't believe so. I think gypsum is often added for structural problems, but it works best if you add gypsum and organic matter together.
Yeah, one organic fertilizer I've been really wanting to get into is biochar that one seems so cool to me.
But I just
haven't had a chance, you know,
look, let me encourage yet caution you with regards to bio char because then just as you would know, that all plants are different, all bio chars are different. So depending on what plant material was used in the first place was charred. To make the biochar, you'll get a very different product. And so, the claims of one biochar can't be applied to another if the feedstock plant material, or even the act, temperature and duration of the charring is different. So just keep that in mind.
So we've come to the end of the episode. Now, Dr. Sam, can you tell the listeners Where can we find out a little bit more about soil? And is there something that you're passionate about that you just want to tell the listeners about,
I want to tell the listeners about soil science, Australia to check out the soil science Australia website, after you've looked at ants fabulous website. And there, you'll find not only lots more information about soils, but you'll also be able to find a Certified Professional soil scientist if you need one for a particular project. And a really exciting thing which is going on in Australia is we've got a new national advocate for soil, we sit in the department of premier and cabinet and that is Penny wirelessly. I'm very excited to be able to work with her to further the appreciation and careful management of soils in Australia. And the federal government is working on a national soil strategy at the moment. So that gets up and gets bipartisan support soon sooner rather than later. So we can look after the soils all across this big, diverse
country. It's the most important resource more important than anything, I would have thought because civilizations rise and fall from this or literally,
absolutely can make money. You cannot
eat money. No. But thank you so much for coming on the show. Dr. Sam, this has just been awesome. And I hope that the listeners have learned just as much as I have today because that was some incredible information. I hope you come back on again, Sam, and you're welcome. Anytime.
It's a pleasure, Dan, great talking to you.
Make sure you check out soar science Australia, as well as the blogs that are linked in the show notes. There's an article I've written that says as an introduction to soil and it has a handy little soil triangle diagram. You'll see what I mean when you actually click on the link. And there's another link to an article I've written that focuses on some of the organisms that we find in the soil, such as bacteria, fungus, insects, insect like little critters, centipedes, millipedes, nematodes, and others as well.

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