Supersonic air knife x-hfa is NOT root friendly in high flow mode (large nozzle, 90psi, 330cfm with 375cfm compressor). It will stir up massive amounts of soil, strip all roots clean of bark and send all silty soil particles airborne.
Handy to have on very rare projects where this capacity helps and roots are irrelevant (aerating my septic field). The "flame" of blue compressed air is wild to see as well.
Otherwise the smaller nozzle and compressor is best.
Wow. that is some serious tree abuse, 802. It is always frustrating to be called in when the outcome is so poor. I asked about Willastonite because I have never used it so was curious. We rarely (almost never) have acidic soils to deal with, so liming is not generally considered.
Go ahead and contact the HBEF. At least go on their website, they have some very helpful/informative articles re this. It is also good to note these amendments were successful without incorporation into the soil.
The apparent popularity of using the air spade is a bit of a concern to me as it pulverizes the soil and destroys aggregation. So it is good to be sure it is being proposed in critical situations, not as a routine maintenance.
Great point regarding air spading not being a part of routine maintenance. Dr. Glynn Percival spoke at the ISA international conference in Knoxville and gave a great talk on passive decompaction. He used vertical mulching and different species of worms to decrease overall bulk density. The study is pretty cool, I'll attach a link to the article.
... I've had very good success utilizing an Airspade 2000 ... Just think of the tool in your hands as a surgical scalpel ...