Agriculture Reference
In-Depth Information
Fertility
The inherent fertility of your soil is dictated by the rock from which it originated. If we
look at a rock like limestone, it's going to be mostly calcium with a bit of magnesium and
not much of anything else — certainly not a well-balanced soil. On the other hand, many of
our soils were brought to us from the movement of the glaciers in the last ice age and so we
may have a soil from a mix of parent materials, which is consequently more balanced.
One of the reasons we want to know about our soil texture is because sand, silt and clay
bring different fertility potentials. Sand and silt come from the same parent materials, and
so have basically the same implications for soil fertility. While there are many different
parent materials, the most common is quartz.
Quartz is mostly silicon dioxide. It generally has a limited amount of minerals in its
composition that will become available to plants, and it can't hold onto other nutrients in
the soil. Soils that are high in sand and silt, therefore, are inherently less fertile than soils
high in clay, not taking into account organic matter. Farmers know they'll get lower yields
on sandy soil because of this lower fertility, which is one reason why adding organic matter
is so important, as we'll see.
While sand and silt are the same other than their particle size, clay is totally different.
Clay is made of many different elements, and the outside of most clay particles are covered
in negative charges because of how the minerals, mainly silicon and aluminum, are chemic-
ally bound together.
Many other minerals in the soil such as calcium, magnesium and potassium are posit-
ively charged, so they attach to the negatively-charged clay, but not to the sand and silt.
The clay also attaches to organic matter molecules in the soil. The fact that clay has these
negative charges is one reason why having some clay in your soil is truly a wonderful
thing.
