Desmond Armstrong wrote:

I found by experiment that if ammonium sulphate is sprinkled on
the clay and watered, it gradually sinks in, and when enough is
applied, the clay becomes soft, crumbly and permeable to any
desired depth.

Read the following two patents:

-----------------------
Method for the manufacture of soil modifiers from waste materials of the
manufacture of titanium dioxide

http://www.patentstorm.us/patents/40...scription.html

This invention relates to a method for the manufacture of soil
modifiers,highly active on compact soils and easy and economical to
apply, from the waste materials consisting essentially of ferrous
sulphate heptahydrate, obtained in the manufacture of titanium dioxide
by the sulphate process.

As is known, many of the world's countries have vast areas of very
compact soil, especially clay soils, little suitable for cultivation.

In these soils the structure is such that the composition of particles
practically prohibits the circulation of air and water and consequently
also the passage of salts from the surface to the root system of the
plants.

In such soils water penetrates very slowly, causing expansion of the
clay particles which induces closure of the pores or prevents further
ingress of water, passage of salts, and circulation of air.

On the other hand during the dry season, water present in these soils,
owing to the continuous capillary channels which are always
characteristic of hard clay soils, works to the surface carrying with
it, also, the salts dissolved in it.

These soils thus come to assume the state of dryness which gives rise to
deep cracks and cementing of the clay particles into a hard and
compacted mass.

Under these conditions the life cycle becomes difficult, not only
because of insufficient presence of water and insufficient aeration, but
also because of the high concentration of salts near the surface.

In methods for modifying the characteristics of compact soils,
especially clay soils, so as to render them suitable for cultivation,
recourse is frequently made to the application of salts, usually ferric,
such as ferric-ammonium alum and ferricsulphate.

These salts induce agglometation of the minute clay particles into
granules, with appreciable improvement in the permeability and aeration
of the said soil. Moreover, a porous granular structure diminishes the
dangers of scouring and soilerosion.

----------------------

Process for the preparation of fertilizers and soil modifiers

http://www.freepatentsonline.com/4058389.html

The solid thus obtained, consisting mainly of ferric hydroxide and of a
lesser amount of ammonium sulphate, may be used directly as a soil
modifier with the additional function of fertilizer.

The compositions thus obtained may be used especially as modifiers of
compact soils, particularly alkaline clayey soils, with the additional
fertilizing function on account of the presence of ammonium sulphate.

In these soils, which are very widespread and are barely suitable for
cultivation, the structure is such as to render the circulation of air
and of water practically impossible due to the arrangement of the soil
particles.

It is already known in the art that in order to modify the
characteristics of compact soils, particularly clayey ones, in order to
render them suitable for cultivation, it is possible to resort to the
application of ferric salts to the said soils. These salts cause the
agglomeration of the minute clayey particles in the form of granules
which give the soil a porous granular structure.

This structure improves the permeability and aeration of the soil, in
that the water and the air can thus readily penetrate into the free
spaces between the individual granules of the soil, with great
advantages for the crops.

--------------------