Soil tests serve as a valuable guide for fertilization practices. Such tests generally
indicate the amounts of available phosphorus, potassium, calcium and magnesium in a soil.
In addition, the pH (acidity or alkalinity) of a soil is also determined. Trained soil
technologists interpret results of soil tests and recommend what fertilization practices
are necessary to produce a desired effect.
At times, a soil may be too alkaline, and it is necessary that an acidifying
agent be added to the soil. Such acidifying agents are sulfur, iron sulfate, aluminum and
others. In many instances, only a slight reduction in reaction is needed. Agricultural lime
or dolomite is used to increase the pH, or "sweeten" the soil. The only way to know what
should be added to a soil to change the pH is to have a soil test conducted. It is a mistake
to try to adjust the pH without knowing what is needed and in what quantity. We often hear
of gardeners who add lime to their soil almost every year. In most cases, the lime is not
needed and an undesirably high degree of alkalinity is reached. Thinking they have not added
enough lime, they add more onto the soil making a bad situation even worse. This practice is
like adding gasoline to a fire to put it out. All we are really trying to point out is
this-don't guess-soil tests. Your guess may be wrong or completely out of proportion as to
the amount of material you really need. Many gardeners feel a soil test is necessary, when
suddenly a plant dies or seems to be on the brink of doing so. After growing well for a
period of years a plant will suddenly wilt and die due to malnutrition. More often the
reverse is true. That is, too much fertilizer has been placed about the plant resulting in
death of the root system. It is rare indeed to find a garden soil so low in nutrients as to
cause the death of a plant.
Some things soil tests do not tell you are the presence of insect or disease organisms and
a lack of water or too much water. In many instances, the sudden death of a plant can be
attributed to one of these factors. Poor drainage, particularly during wet weather, is one
of the major causes of plant decline or death. We often forget that oxygen is needed in
greater amounts than other elements such as nitrogen, phosphorus, potassium, etc. Wet soils
contain little oxygen, which is available to the roots. When this condition exists, the
plant's root system ceases to perform its vital function of absorbing water and nutrients
from the soil. If this waterlogged condition persists, the root system will die, resulting
in death of the entire plant.
Another thing not ordinarily revealed is the presence of herbicides or weed
killers. The indiscriminate use of these chemicals often results in sudden death of plant.
Ordinary soil testing will not reveal the presence of nematodes in the soil.
These microscopic worm-like animals damage plants by feeding on their root systems. Affected
roots appear shriveled, blackened and stubby and there generally will be an absence of white
feeder roots.
The next time you have a soil problem you think might be related to lack of
fertilizer, examine your growing conditions (water, drainage, insects, disease and nematodes)
to see if these are not causing the problem. If none of these problems exist, then have your
soil tested.
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