The basics are that it (or any clear shampoo) can be used at 2 to 4 ounces per thousand square feet per month to lighten, loosen, and make soils more diggable.

(Sidenote: This is the second step out from a stabilized formula Andy Hejnas and I developed, and not quite as effective as the original, but it does work. The original uses sodium laureth sulfate, an ethoxylated version of coconut oil, or sodium lauryl sulfate, also a coconut oil derivative, as the primary surfactant in a higher percentage than you'll ever find in shampoo--although some floor degreasers would have it at this rate.

I've also used home-made soap derived from the sodium salt of coconut, palm, lard, castor, and/or olive, but that's quite another story).

Soil Biology and Fungi:

Long-story-short, surfactants or soaps have a double-ended molecule. One part loves water and will bury its nose into any water droplet it encounters. The other end (and often side branches) hate(s) water and will do anything it has to do to avoid it. Water droplets, which normally have a very high surface tension, end up with surfactant or soap molecules buried in the surface, reducing surface tension and enabling the water to become wetter.

Fungi like that (they also like those molecules as they're fatty acids and, hence, dinner). The more penetrable water helps to moderate the environment for the fungi as well, enabling them to grow. Fungi essentially form the lungs of the soil, expanding and growing when moist, shrinking and allowing oxygen in when dry.

One cubic centimeter of healthy soil can contain miles of fungal hyphae, but since they're only one cell wide they're not visible.

Growing fungi then bind soil particles together into aggregates, increasing the soil tilth, increasing water capacity, and increasing water penetration.

That's the biological part--and it's vastly enhanced by also feeding organically at least once per year to assure that adequate food for the fungi is also there.

Soil Chemistry:

Chemically, the situation is more complex. The CE (Cation Exchange) points of the soil bind one end of the molecule, the AE (Anion Exchange) points bind the other on a different particle. Being very, VERY large as compared to a calcium or other soil ion, the binding is wide, loose, and large enough to allow air and water in between bound particles. That increases tilth at the particle level, but this is more temporary as the soap molecule is biodegradable. The fungi stick around and, if fed, continue to increase over time.

The chemical process will, reasonably quickly, flocculate (pull together) a deflocculated (fallen apart and plated up) soil into peds (small bits and pieces all stuck together). However, it'll fall apart again in a few years if not maintained, if further structural damage is done (as by tilling), or if excessive amounts of some elements are present or added (sodium and magnesium, most notably).

You can manage the same process just by feeding organically, which will encourage the fungi, but adding the soap accelerates the soil changes. Use can be discontinued as soon as the soil's at your desired softness and pliability.

Dry Spot and Hydrophobic Soils:

Dry spots are often caused by wax or grease buildup from bacterial decay in the soil (or, why we generally favor fungal decay in soils, although bacteria are useful even in exceedingly large numbers). Use of shampoo dissolves the grease (and wax, but more slowly in that case) and washes it away, just as shampoo removes grease and foreign material from your hair. Multiple applications may be necessary in heavily clogged soils.

Dry spot is much more of a problem in locales such as golf greens, and not generally nearly as problematic in the home lawn, which features a much more balanced soil biology. In your lawn, for every bacteria that produces copious grease, there are other species that consider that grease an excellent snack. This is far less true in pure sand, heavily managed, and frequently chemically damaged, golf greens where the soil biology is stunted and populations of many species is inadequate.

Hydrophobic soils are caused by exceedingly dry conditions (where the water tension of the water droplet is greater than the soil's attraction for the water). They'll eventually penetrate, but minor rainfalls or heavy rain on dry soil may result in runoff, and in the soil not absorbing as much water as it could.

Soap can and will decrease the surface tension of the water and increase penetration and absorption of the water. I occasionally spray just before a large rainfall following a dry spell--and have some vastly amusing photos of a river entering the north side of my property and disappearing into the ground long before it exits the southern end.

A Note on Sodium:

If you follow my soil readings, I frequently mention sodium as a useless ion that I occasionally dispel from the soil profile when amounts rise too high. Consequently, it may seem that the use of sodium lauryl/laureth sulfate and other sodium-bearing chemistry is imprudent.

If this concerns you, search for shampoos using alternate surfactants such as ammonium laureth sulfate, or potassium-based soaps. Both are fairly common.

However, sodium build-up is of no great concern, as the below shows.

Most soils contain at least 1 pound per thousand square feet of sodium ions (these will either bond to the exchange points or find a negatively charged ion and produce a compound). There are certainly exceptions and soils that contain far less or far more sodium are easy to find.

Most shampoos contain sodium-bearing compounds at a maximum of ten percent of their weight (the remainder will be other, weaker surfactants, water, fillers, scent, color, and emollients). Sodium laureth sulfate has a molecular mass of 420 g/mol. Sodium has a molecular mass of 23.0 g/mol, and the molecule contains exactly one sodium ion.

The sodium weight is, therefore, 5.5% of the total mass of the surfactant.

Even assuming one were to use 100% sodium laureth sulfate (which would be inadvisable in the extreme as it is a salt) at 4 oz per thousand square feet, each application would add 0.22 ounces of sodium per thousand square feet.

To double a completely tolerable 1 pound of sodium per thousand square feet to 2 pounds per thousand square feet would require 18 applications--4.5 pounds--of pure sodium laureth sulfate. Which also assumes that one hundred percent of the sodium remains in the soil, a dubious assumption at best as sodium flushes over time and only salt-treated or very arid soils tend to suffer from buildup.

The average user of 10% SLES in 90% water (and other materials) would require, at 4 oz per month and no water flushing, 180 months of consecutive use (15 years) to add 1 pound of sodium to the soil.

Sodium can be easily flushed by adding gypsum and irrigating thoroughly (or allowing rainfall to rinse the soil) should it become a concern in those 15 years.