New Air Knife

[appalachianarbo]

My main goal was to reduce compaction and create air space. Vermiculite is an excellent rooting medium while at the same time maintaining air space. A soil/loam/compost/sand/gravel, etc. mix has less air volume and would compact easier than straight vermiculite. Yes, a loam mixture would have more nutrients & organic matter, but the existing soil already has enough to support the roots. Vermiculite is also much easier to apply and handle.

 

[treevet]

I used the air knife on 3 jobs last week. It was a cold morning, so there was a 3" frozen layer on top. Luckily, the first job was in the woods, and there was a layer of leaf litter over much of the surface that kept the soil underneath from freezing. I excavated about 2' of soil from around the trunk of a 20" hickory. You can see the old soil line in pic #2.

It was warmer out by the time I got to the second job - aeration of a codominant hemlock. The holes were ~ 2" deep. I backfilled with coarse vermiculite. Took about 30 minutes total for ~ 50 holes.

How come there was 2' of soil covering the floor of the woods? Just taking it away from the trunk won't help the roots. Did you remove 2 feet of soil from the entire crz and take it off the site? Hickories are very sensitive to grade changes. Like to hear more of the story and the plan, history and desired results. Thanks

 

[appalachianarbo]

This tree is sitting in the woods at the end of a street that will soon have houses built on it. I assume that the soil was dumped there to get rid of it from some other site nearby. It's been there for at least 2 years. My main goal was to get it away from the trunk, expose the root flare, and see exactly how much needs to be done for this tree. The owners wish to save it as part of their preservation plan. I did not uncover the root zone - that will be done during grading in the spring (yes, I have a preservation plan in place, and the air knife will most likely play a big role in moving the soil, as opposed to heavy equipment). Luckily, this tree was not that sensitive to its grade change and has done very well with the piled soil on its root zone. No dieback, no trunk/root rot (that I can see). Another reason for leaving the soil is to provide a barrier for the roots during land clearing operations. Leaving the soil will provide a buffer for falling brush, dragged logs, etc.

 

[treevet]

It usually takes a few years and up to 7 or 8 years to see the effects of grade changes. 2 years is no way an indicator of adaptability.

Hickory is one of my favorite trees. We have had severe drought around here and most trees look terrible. Hickories (mostly Pignut and Shagbark) took it all in stride as they have a serious tap root. Because of that you seldom find them in nurseries except small stock in containers. I planted a Mockernut in my yard and a Pignut that I dug out of the woods. The Mockernut was a container tree and both are doing great as I baby them and they are fenced in and protected.

I wouldn't count on backfill to protect the trees from heavy equipment running over their roots. I would tape of the CRZ of any important trees if you are responsible. Good luck in all these projects. I, for one, would like to hear more about them as they play out.

 

[John Paul Sanborn]

A soil/loam/compost/sand/gravel, etc. mix has less air volume and would compact easier than straight vermiculite. Yes, a loam mixture would have more nutrients & organic matter,

I think you are missing the relationship of micropore vs macropore and how they relate to plant health.

Getting organics into the macro pores (which is all you have with an even particle size/distribution environment with a single type of fill) will help with the bulk density, holding capacity and perc rate.

The last is because water movement through a material is by surface action. To pass from one well defined stratum to the next, the homogeneous stratum must be saturated.

It is best to use a heterogeneous medium and mix it in with the native soil under it to avoid a well defined layer.

 

[appalachianarbo]

It usually takes a few years and up to 7 or 8 years to see the effects of grade changes. 2 years is no way an indicator of adaptability.

Yes, I understand that. Perhaps I should have said, "So far, the tree has done very well..." I'll keep monitoring it throughout and after the construction process.

I wouldn't count on backfill to protect the trees from heavy equipment running over their roots. I would tape of the CRZ of any important trees if you are responsible.

I assumed that by saying a tree preservation plan was in place that it was implied that there were exclusion zones prescribed for all phases of construction. It is not possible in this situation for the exclusion zones to cover the entire root zones of all the trees to be saved. Therefore, the fill will provide some barrier to equipment/felling for the sections of root zone that are not protected by an exclusion zone. There will not be heavy equipment allowed anywhere except the driveway and home footprint, but skidding of logs, etc. will have to occur across some root zones.

 

[appalachianarbo]

Getting organics into the macro pores (which is all you have with an even particle size/distribution environment with a single type of fill) will help with the bulk density, holding capacity

I would have to argue that vermiculite has a lower bulk density and a higher water holding capacity than a vermiculite/organics mixture. The macropores created in the backfill of vermiculite will provide for root growth as well as percolation.

As for perc rate, the vermiculite is covered by soil removed from the trenches. The air knife creates a very fine soil with little to no structure and very fine particles. These soil particles will mix with the vermiculite over time and create a heterogeneous mixture without a well defined boundary between the fill types. Organic matter will be naturally added by the decomposition of the mulch over time.

Whaddya think- Make sense of am I just spouting off a bunch of BS?

Thanks for the soils review JPS

 

[John Paul Sanborn]

I'm not saying that it is bad practice, just not the best. As you say, the airtools will leave a very fine soil behind. (along with around a 25% loss to drifting) Consistent ped size will compact faster then a natural heterogeneous (or should I say mixed or varied?) particle size.

Yes, over time there will be infiltration of organics into the vermiculite trenches, but...

We still have the movement of water from strata to strata. So the top organic layer needs to saturate for water to move into the vermiculite, then the vermiculite needs to saturate.

This is the same a s the debunking of putting gravel in the bottom of a planting pit for drainage. Though you probably will not get the anaerobic conditions that occur in that situation.

Another problem is that water will tend to drain at these barriers if there is enough grade.

Vermiculite will have large (macro) pores, these help with perc, which is the primary driver of deep gas exchange. The micro pores are what hold water for the plant to use long term, I doubt the efficacy of vermiculite in this.

Then there is the loss of microbiota in the system. You are basically going from a depleted environment of compacted soil, to one of a homogeneous mineral.

My point is that using a "fortified" mix of material (with some clods for a inconsistent ped size) is a better practice.

Thanks for the soils review JPS

Got to build it so others can understand it. If a few people learn something, then it has been worth my time.

 

[appalachianarbo]

Don't get me wrong - I'm all for building soil structure and organic matter levels, creating aeration, drainage, root growth, and gas exchange. If it were up to me, I would have replaced much of the root zone soil (down to a depth of at leaast 12") with a 50/50 mix of native soil and compost/sand/vermiculite/peat moss and mychorrizal inoculant. The budget was tight for these jobs, and so for meeting the primary objective - reducing compaction quickly and for the longest time possible - trenches with vermiculite and a mulch topper will satisfy me.

Good advice, all. Thanks

And yes, using the air knife is a DIRTY job! I used a full face shield, and would try to wipe built up soil off the outisde of the shield. Turns out, the dirt was on the inside, and was mixing with the condensation from my breath. Nice!

 

[John Paul Sanborn]

Turns out, the dirt was on the inside, and was mixing with the condensation from my breath. Nice!

I gave up on the face shield and when with goggles and respirator. Among other things, my respirator and sheild got in each others way.