Roger: 0:02

Talking Trees with Lillie and Jad. Welcome to Talking Trees. Today we review several sources on improving soil quality for urban trees. The research covers a range of methods, including the effects of compressed air injection on tree growth, soil decompaction through aeration, fertilization and mulching, as well as phytoremediation techniques like phytostabilization, phytoextraction and rhizodegradation. We also examine the performance of TerraVent, a device using compressed nitrogen for soil decompaction, and its impact on soil structure.

Jad: 0:44

Hey everyone. You know, as arborists, we're always facing that challenge of keeping urban trees healthy.

Lilly: 0:50

Oh, absolutely.

Jad: 0:51

Especially when they're dealing with compacted soil.

Lilly: 0:53

Yeah.

Jad: 0:53

Construction, foot traffic, you name it. It seems like everything's working against them.

Lilly: 0:59

It's tough out there for a tree sometimes.

Jad: 1:01

And I know we all know about tilling before planting, but that's not always an option, nope, especially once a tree's already established right.

Lilly: 1:07

Right.

Jad: 1:08

So today we're going to explore some other ways to tackle this compacted soil problem.

Lilly: 1:12

Okay, sounds good.

Jad: 1:14

Techniques I'm sure you're already familiar with compressed air injection and soil amendments. And to help us really dig into the research, we have an expert here.

Lilly: 1:22

Well, I'm happy to be here.

Jad: 1:25

Now I have to admit, when I first heard about compressed air injection, I was intrigued.

Lilly: 1:29

Oh yeah.

Jad: 1:30

It sounded almost too good to be true.

Lilly: 1:33

I can see why.

Jad: 1:34

Like magic, just blasting away compaction with air.

Lilly: 1:37

Yeah, it does have a certain appeal, doesn't it?

Jad: 1:40

But as with anything, it's probably more complicated than that.

Lilly: 1:43

You got it. There's always more to the story.

Jad: 1:45

What's the research really say about how well this technique works?

Lilly: 1:49

Well, the basic idea behind compressed air injection is sound.

Jad: 1:53

Okay.

Lilly: 1:54

You know, it makes sense to break up that compacted soil.

Jad: 1:57

Give those roots some room to grow.

Lilly: 1:58

Exactly, Give them space to breathe. But the thing is, how effective it is really depends On what. A couple of key things soil type and moisture content those are biggies.

Jad: 2:12

That makes sense. I mean, as arborists, we know we're always dealing with different soil types.

Lilly: 2:16

For sure, every site's a new puzzle.

Jad: 2:21

And moisture levels. Those are always changing, oh yeah, Constantly in flux. I actually came across this study from 1993. It looked at using compressed air injection around mature street trees.

Lilly: 2:28

Interesting.

Jad: 2:29

They found that birch trees when they were in compacted sandy loam. They responded well.

Lilly: 2:34

Okay, so that's good news for the birches.

Jad: 2:35

But sweet chestnut trees, those that were in clay loam not so much.

Lilly: 2:40

Hmm, so soil type definitely plays a role.

Jad: 2:43

Why would that be that difference?

Lilly: 2:45

It all boils down to something we call soil plasticity, basically, how easily the soil changes shape.

Jad: 2:52

Ah, okay, so like how moldable it is.

Lilly: 2:55

Exactly. And when you're injecting the air, you want the soil to fracture. You want to create those air pockets.

Jad: 3:01

Right. Give the roof some breathing room.

Lilly: 3:03

But if the soil is too dry, it'll fracture too easily.

Jad: 3:06

And the air just escapes.

Lilly: 3:08

Yep, no good. And if it's too wet the soil it just collapses back on itself.

Jad: 3:13

Ah, so it's all about finding that sweet spot.

Lilly: 3:15

Yeah, you need that Goldilocks moisture level Not too wet, not too dry, just right for those lasting air channels.

Jad: 3:21

So it sounds like it's not just about grabbing the air compressor and going at it.

Lilly: 3:25

No, not quite that simple, unfortunately.

Jad: 3:28

You need to look at those soil conditions.

Lilly: 3:29

Absolutely.

Jad: 3:30

Figure out that moisture level. Use your judgment Right.

Lilly: 3:33

Right. Your experience as an arborist really comes into play here.

Jad: 3:37

But even if you've got those perfect conditions, there's still a question.

Lilly: 3:41

And what's that?

Jad: 3:42

Do those fractures actually help the roots grow better?

Lilly: 3:45

That's a great question, and that's where things get a little more complicated. Oh how so Well, even if you're seeing good fracturing, it doesn't always mean a change in bulk density.

Jad: 3:55

Oh, I love that. Remind me what that is again.

Lilly: 3:56

It's basically a measure of how tightly packed those soil particles are.

Jad: 4:01

Okay, right, right.

Lilly: 4:02

And for good root growth. We want a lower bulk density. We want it looser, not so dense.

Jad: 4:07

Makes sense. So more space for those roots to spread out.

Lilly: 4:10

Exactly, there was this study back in 1990. They looked at a few different air injection machines, okay, and they found that they were seeing fracturing.

Jad: 4:19

Good sign, right? You'd think so, but it didn't always mean a big change in the bulk density Interesting, so you could be seeing those cracks thinking you're doing a great job but.

Lilly: 4:28

But those roots might not be getting the benefits.

Jad: 4:31

It's not actually changing the soil structure.

Lilly: 4:33

That's a really important point for arborists to keep in mind. We don't want to be fooled by appearances.

Jad: 4:38

Absolutely. We need to make sure those roots are actually getting what they need.

Lilly: 4:44

Exactly, and even when you do get a reduction in bulk density. There's another issue what's?

Jad: 4:47

that.

Lilly: 4:47

The area of soil that's actually affected. It might be pretty small.

Jad: 4:51

Compared to.

Lilly: 4:53

The whole root zone of the tree. Ah, I see You're creating a few channels of loosened soil.

Jad: 4:58

But it's not really making a big overall difference.

Lilly: 5:01

That's the challenge.

Jad: 5:02

So it sounds like compressed air injection has its place.

Lilly: 5:05

It definitely can be useful in certain situations.

Jad: 5:07

But we need to think about how to make those improvements last longer.

Lilly: 5:11

You're thinking about soil amendments?

Jad: 5:13

Exactly, that's got to be the next step, right.

Lilly: 5:15

You got it, and that's where we get into some really interesting strategies, and when we start talking about soil amendments, we're getting into some long-term solutions.

Jad: 5:24

Yeah, it's not just a quick fix right. We're actually trying to improve the soil for the long haul. Exactly, we're thinking about the tree's future. This is where it gets really interesting. I found a study from 2011.

Lilly: 5:36

Oh okay, what did they look at?

Jad: 5:37

They combined air injection, compost and mulch.

Lilly: 5:40

Wow, the whole shebang.

Jad: 5:42

Yeah, they wanted to see if this triple threat could make a real difference.

Lilly: 5:45

A multi-pronged attack. I like it.

Jad: 5:47

They called it the AFM treatment Catchy right.

Lilly: 5:51

Gotta love a good acronym.

Jad: 5:52

So what did they find? Did it actually work?

Lilly: 5:54

They tested it at four different sites, all urban areas.

Jad: 5:58

Okay, typical challenging conditions then.

Lilly: 6:00

Exactly the kind of places we work in all the time Red maple trees all struggling in those compacted, nutrient-poor soils.

Jad: 6:08

The classic urban tree struggle.

Lilly: 6:09

Oh yeah, but the results, they were pretty impressive.

Jad: 6:13

In what way?

Lilly: 6:14

Especially when you look at soil strength. At all four sites, afm did a great job, much better than doing nothing at all.

Jad: 6:21

So combining the approaches was a winner.

Lilly: 6:23

Seems like it. But they didn't stop there. They also tested each component on its own.

Jad: 6:28

Air injection, compost and mulch separately.

Lilly: 6:31

You got it. Wanted to see what each one was bringing to the table.

Jad: 6:34

Interesting what happened.

Lilly: 6:36

Well, air injection by itself, it did reduce soil strength at first.

Jad: 6:40

Oh, so it worked to some degree.

Lilly: 6:42

Yeah, but it was short-lived. After three years those soils were pretty much back where they started, ah so just poking holes isn't enough. Nope, you need something more to keep that structure from collapsing.

Jad: 6:52

Something to maintain those changes.

Lilly: 6:54

Exactly, and that's where compost and mulch really shine.

Jad: 6:57

Because they add organic matter.

Lilly: 6:59

Bingo Compost improves that soil structure directly and mulch acts like a protective layer. Keeps the soil moist. Adds even more organic matter over time.

Jad: 7:09

Double whammy.

Lilly: 7:10

Yeah, they work together and the study backs this up. They looked at soil organic matter levels at the sites. That started with moderate levels.

Jad: 7:18

Okay.

Lilly: 7:19

AFM and mulch alone both boosted those levels.

Jad: 7:23

So mulch wasn't just a bonus.

Lilly: 7:24

It was a key player. Sometimes, the simple solutions are the best.

Jad: 7:28

Mulch the unsung hero. But what about keeping those trees fed? You mean fertilizer, good point.

Lilly: 7:34

They compared the full AFM treatment where they mixed fertilizer into the soil.

Jad: 7:38

Right right.

Lilly: 7:39

To just applying it on the surface. Get this At almost all the sites. Afm was better.

Jad: 7:44

Really so. Even though we usually apply fertilizer on top, getting it down deeper makes a difference.

Lilly: 7:49

Seems that way. I guess mixing it with the air tillage and compost helps.

Jad: 7:53

Keeps it where the roots can access it.

Lilly: 7:54

Yeah, Maybe surface application leads to more runoff. You know those nutrients just washing away.

Jad: 8:00

Especially in compacted or sandy soils.

Lilly: 8:02

Exactly. It really makes you think about how we apply fertilizer.

Jad: 8:05

How to get the most bang for our buck. But you know what else arborists are always thinking about.

Lilly: 8:10

What's that?

Jad: 8:11

Water, especially with all these droughts we're seeing.

Lilly: 8:14

Oh yeah, water's gold these days.

Jad: 8:16

Did the study look at how these treatments affect soil moisture?

Lilly: 8:19

They did. And guess what? Both AFM and mulch alone led to significantly higher soil moisture.

Jad: 8:26

Mulch again. It's like a superhero for soil.

Lilly: 8:28

Improves structure, adds organic matter and helps those trees hold onto water. What can it do?

Jad: 8:34

Hmm, amazing. Okay, we've covered a lot here. Any key takeaways for our listeners out there in the field.

Lilly: 8:41

I think there are three big lessons here.

Jad: 8:43

Okay, lay them on me.

Lilly: 8:44

First, that multi-pronged approach like AFM Probably better than relying on just one thing.

Jad: 8:51

Right Attack from all sides.

Lilly: 8:53

Second mulch, Don't underestimate it. It's simple but powerful.

Jad: 8:59

Definitely a favorite tool in the arborist's arsenal.

Lilly: 9:02

And third, that fertilizer thing Seems like incorporating it into the soil might be the way to go.

Jad: 9:08

Get it right to the roots.

Lilly: 9:09

Exactly and something else. The study mentioned something we always need to remember.

Jad: 9:13

What's that?

Lilly: 9:14

Site-specific solutions. They found that how well these techniques worked it depended on what the soil was like at each site.

Jad: 9:22

Ah, makes sense, Not a one-size-fits-all situation.

Lilly: 9:25

Nope, we got to be soil detectives.

Jad: 9:27

Analyze each site and come up with a plan based on what we find.

Lilly: 9:30

Exactly, we're like soil doctors.

Jad: 9:32

Figuring out the best treatment. Okay, we've talked about dealing with compaction, but what about when the soil is actually contaminated?

Lilly: 9:39

Ooh yeah, that's a whole other challenge.

Jad: 9:41

Especially in urban areas.

Lilly: 9:42

For sure. All sorts of stuff can end up in the soil.

Jad: 9:45

So how do we deal with that?

Lilly: 9:46

Well, there's actually some really cool research on using plants themselves to help clean up contaminated soil.

Jad: 9:51

Plants as cleanup crews.

Lilly: 9:55

Yeah, it's called fighter remediation.

Jad: 9:56

Well, I want to thank you for sharing your expertise with us today, and to all our listeners out there, thanks for joining us on this deep dive into the world of soil remediation.

Lilly: 10:04

It's been a pleasure.

Jad: 10:05

We hope you've learned some new tricks to help those urban trees thrive even in those tough conditions. Keep those saws sharp, keep learning and we'll see you next time.

Roger: 10:20

Thank you for your attention. In today's discussion, we examined several methods for enhancing soil quality in urban forestry, including compressed air injection, conventional decompaction techniques with aeration, fertilization and mulching, as well as various phytoremediation strategies. And mulching, as well as various phytoremediation strategies. We trust this analysis provides valuable insights for informed urban tree management.