Agriculture Reference
In-Depth Information
Figure
9.9.
Compost pile with fresh organic matter on top and composted organic matter
at bottom.
of this organic matter. The soil becomes deficient in nitrogen, and plants cannot obtain
enough of this nutrient and their growth is decreased. Thus, these types of materials are
best composted or the decomposition allowed to continue for some time before crops
are planted. This does not apply to legumes because they fix their own nitrogen.
Like fresh manure, a freshly plowed under green manure crop contains a great
amount of readily decomposed organic components. The decomposition of these can
lead to oxygen depletion in the A horizon, and thus the soil will not be suitable for
immediate crop production. However, green manure crops can be very beneficial in
increasing a soil's organic matter and its structure.
9.8
SOIL BASIC FERTILITY
In this section we will not discuss fertilizers because they are discussed in detail in
Chapter 11. Basic fertility is the innate ability of soil to supply plant nutrients to crop
plants. Some soils will have naturally high levels of some plant nutrients; others will
have low levels. Because of its chemistry nitrogen is never likely to be at high levels
in soil except where large amounts have been applied as fertilizer or if the soil is
near some natural source, such as a soil that receives the drainage from a bat cave, a
livestock holding area, or is a nesting area for thousands of birds. Legumes fix their
own nitrogen from the air and are thus independent of other nitrogen in the soil.
However, high nitrogen levels in soil reduce the amount of nitrogen legumes fix.
Unlike nitrogen, some soils can have naturally high levels of phosphorus, and others
can have high levels of potassium. It is not common, however, to find soils with both of
these nutrients at high levels. High levels of phosphorus can occur around phosphate
deposits such as those in the midwestern part of Florida. In soils developing from
parent material containing large amounts of potassium-bearing minerals can have
large amounts of potassium such as the soils in northwestern Luzon in the Philippines.
