HEAVY APPLICATIONS SOMETIMES NEEDED ON CLAY
Following World War II, a rush to suburban living absorbed millions of acres of farmland around American cities. Many farm owners, realizing what was going to happen, stopped regular soil maintenance and let crops use up fertility that had been built up through the years.
In such soils, potash (even on heavy clays) was depleted to a point where deficiency symptoms developed. I have seen a number of speculative housing developments where the minimum of black soil that was applied came from just such impoverished former farm fields. Heavy applications of potash were needed to bring the soil up to good tilth again. As a result, even where black clay soil is deep, I recommend that you apply extra potash if you are developing a garden in a new housing development. Once clay soil has been brought up to a high potash level, ordinary applications plus compost should keep it will supplied.
SODIUM VS. POTASH
Chemically, potash and sodium are enough alike so that many plants will absorb sodium if potash is in poor supply. This presents a problem in certain western soils where sodium is high. Large amounts of potash are needed in such soils to override the soduim
and thereby keep plants from absorbing this useless and sometimes harmful chemical.
There are, however, a few plants which seem to need small amounts of sodium for normal growth. Among these are beets, cabbage, celery and turnips. If these do not do well, the use of nitrate of soda as a source of nitrogen will sometimes increase yield and crop quality.
Other crops, particularly asparagus and tomatoes, seem to be able to use a certain amount of sodium if potash is low, yet seem to be neither hurt nor helped by the substitution-up to a certain point. If sodium is too high, they will suffer.
In general, with these exceptions, sodium can be considered non-essential as a trace element and definitely harmful if present in quantity. In fact, many crabgrass-killing chemicals contain a form of sodium.
THE "MINOR" ELEMENTS
The word "minor" as applied to elements such as iron, boron, magnesium, calcium, sulfur, zinc and so on, does not refer to their importance but to the amounts present in soil for use by plants.
CALCIUM AND MAGNESIUM
Although used by plants for different functions, calcium and magnesium should be discussed together. They often occur in the same "limestone" used for "sweetening" acid soils. Thus when a liming has a favorable effect on plant growth it is hard to tell whether the improvement is due to changes in pH, or to the effect of calcium on plant cells, or to the vital effect of magnesium on chlorophyll formation