cement
together the fine clay particles and in that way create air spaces so
greatly needed in tight clay soils. Lime is beneficial, too, in the case
of soils which have a large proportion of sand or large particles, and
serves as an agent in creating a better condition of tilth and of moisture
retention.

It makes little difference in what form lime is applied. It may be
purchased and applied in the form of ground limestone, a rock rich in
calcium which has been mechanically ground to a very great degree of
fineness. It can also be applied in the form of hydrated lime. This is
obtained by heating ground limestone and slaking it by adding water. A
common example of this is the slaking of lime for whitewashing purposes.
Another good source of lime is finely ground shells of oysters or other
forms of sea life which collect the calcium from sea water and deposit it
in their shells.

_Adjusting the Water Content of Soils._--Aside from the supplying of water
by irrigation, a rather costly process under most conditions, the water
resources of most soils can be greatly increased by adding to their humus
content. Humus, which, it has been pointed out, is decaying vegetable
matter, serves as a sponge for the absorption of soil water and for
underground water supplies. Therefore, the more humus that can be plowed
into the soil, other conditions being equal, the greater is the ability of
the plants growing in that soil to withstand drouth. As soils are
cultivated, the tendency is for the humus to become "burned out" and to
have a reduced moisture-holding capacity. To overcome this tendency, it is
necessary to add vegetable matter to the soil whenever it is possible.
Incidentally, the incorporation of large quantities of humus in the soil
creates a condition of acidity which may call for the application of lime
as a corrective.

There are many acres of land which contain too much water in the area that
roots should penetrate to permit of optimum plant growth. Roots of most
plants will not penetrate where there is an excess of water, and air
cannot circulate where moisture is superabundant. Usually these conditions
exist where the soil is of a clayey nature. The abundance of water may be
caused by the inability of surface water to percolate through the soil. It
may take so long, due to the nature of the soil, for this water to pass
through the lower depths of subsoil that the roots of plants are destroyed
by lack of oxygen. In su