Root length: Is this normal?

[Dargin]

I visited my uncle's house today to check up on his lawn. I was able to see a cross section view of the soil as he's in the process of building a stone retaining wall. I was kinda surprised by what I saw.



Some of those roots are over a foot long. Makes me scratch my head; their soil always feels tight and compacted to me. I couldn't imagine roots making it that deep.

I also noticed some sort of thin dary grey band about a foot down. I'm kinda curious what that could be if anyone has any thoughts.



Thanks.

[MorpheusPA]

A foot's within normal range, depending on the soil. My roots (well, the grass', my personal roots depend on how long I stand in a given location in the rain) don't reach that deep. Six inches, yes. Eight, sometimes. A foot, no.
How deep a root will go depends on the soil, how deep oxygen can penetrate (root growth requires oxygen in the soil), watering (grasses that aren't irrigated or are irrigated deeply and infrequently will tend to have the longest roots), and to some extent on the age of the grass (very young grasses simply don't have the time to grow deeper root systems and take some years to develop).
Very sandy soils, with a lot of air penetration, will tend to encourage the deepest roots. They're also well-draining soils (hence the most air-filled) and rather dry, so roots have to go deep to get enough water.
Silty soils are more compact, on average, and roots don't go so deep. Clay will tend to have the shortest roots, but again, only on average and there are certainly exceptions.

When we test soils, we only test to four inches. Most of the feeder roots are clearly in the top four inches. There are certainly deeper roots there that do tap deeper resources, but they're mostly there to tap water. Still, it's not that they won't grab calcium or anything else if it's available (and that's critically important for soil succession as well, or why the meager dandelion is incredibly important in bad soils, and the role sunflowers...but I digress).

That's not to say that one soil is "better" than another as water retention of the soil itself also comes into play; overall, silt holds the most usable water per gram of soil, and given wicking, provides the most to the roots before going dry. But it has some disadvantages as well, so... We can go on for days about soils if you let most of us.

That white band? Off the cuff and without a closeup, it appears to be a sandy layer forming the base of the B layer as it transfers into the subsurface soil. The soil above is likely the same, just darker due to organic matter working in as it sloughs off the roots over the years. Upward still from that, darker again due to increasing organic matter as you go.

If you jar test that soil, I'm going to guess, just from looking (which is not a safe way to read a soil, but I'll go out on a limb here) that you'll find a lot of sand, some silt, and very little clay.

[Dargin]

Wow, thanks for all of that info. The roots did have me wondering about the reasoning for a 4" testing depth, thanks for clearing that up. I appreciate the description of the soil layers. I didn't realize the progressive darkening was attributed to OM. I need a course in the Visual Literacy of Soil.

I probably should have mentioned that the lawn is only about 4 years old. And it's odd that they are typically shallow and frequent when it comes to irrigation. The lawn will very likely bottom out with the upcoming heat...heh

BTW: Seems you nailed the soil.
The jar test I did last year yielded an inch of sand, just under a half inch of silt, and 1/16 inch of clay. The TEC was 3.2, OM ~4.

[bpgreen]

What kind of grass do you have? I've got native grasses that have roots that go 8 feet deep.

But for more normal turf grass, it usually depends on soil conditions, gras species and watering practices. If y you've got kbg and water every day, the roots will likely be pretty shallow. If you wager less frequently and more deeply, the roots will be deeper.

[Dargin]

8 foot roots? That's amazing. I didn't know that was possible.

He had his lawn hydro-seeded about 4 years ago with Home Run perennial rye, Salem red creeping fescue, and Blue Saphire kbg.

[MorpheusPA]

There have been (questionable) reports of alfalfa roots penetrating into mine ceilings thirty feet down. Certainly tap roots are capable of going down very, very deep indeed in proper conditions.

On the other hand, some swamp tree roots actually grow upward for proper aeration and open channels into the air. They've evolved to do that.

If there's little water, but plenty of oxygen available, the roots just keep going. If there's too much water and not enough air, they tend to rot or compensate by air-rooting. That "meh" photo I've posted is in a locale where spring tends to be sodden and the roots drown and rot. They only go down 4" max. They do grow deeper in late spring, but they don't have much time to penetrate deeper.

I've compensated with metric tons of organic matter and gallons of soil conditioner. It's helped, but..

[Dargin]

I hope those alfalfa root stories are true; too good.

I guess with all I've heard about the perils of shallow frequent irrigation, and knowing that's exactly how he waters, I expected to see a wimpy root system. I guess the sandy soil allowed enough oxygen for some roots to really go on the hunt regardless. It was very surprising to see this. Pretty cool.

[schreibdave]

Here's mine. This is 11 mos old kbg. I'd say that some of those roots are 18" long. But I wonder if some of them went horizontally rather than down.

[MorpheusPA]

Is this going to become a thing? https://youtu.be/rhLjfjT18_E

But seriously, it's fun to see these. There's absolutely no reason roots can't go this deep, or deeper, in many soils.

But there's also no reason to panic if somebody cuts their soil and sees shorter roots and they're following all the rules. Their soil could be dense, generally not as accepting of air or, like mine in the swale, regularly saturated and oxygen-starved for months at a time. Sometimes nature, the Universe, and simple geology (or grading) work against us.