Nature Bulletin No. 707   March 2, 1963
Forest Preserve District of Cook County
Seymour Simon, President
Roberts Mann, Conservation Editor

****:SOIL MINERALS

We all depend upon the land Our food is obtained from plants and 
animals -- bread and meat, potatoes and fish, fruit and eggs and milk 
and the rest of it. Our livestock feed on plants and plant products such 
as grass and grain. Plants, by means of their root systems, take moisture 
and nutrients from the soils on which they grow. Their food values, for 
us or for animals that furnish us food, depend upon the available 
nutrients in those soils.

Soils contain solids, water and air. The solids, the bulk of a soil -- 
except in purely organic types such as peat and muck -- are mostly 
mineral materials. Ordinarily they also contain some organic material: 
decayed and decaying remains of plants and animals.

At least 16 elements, called plant nutrients, are considered necessary for 
optimum growth, development and food values in plants. Of these, 
carbon, hydrogen and oxygen are obtained largely from the water and 
air. From the soil solids, plants obtain six called macronutrients, that are 
used in large quantities: nitrogen, phosphorus, potassium, calcium, 
magnesium and sulfur.

Seven other elements, called micronutrients, are just as essential for 
plants but needed and used only in very small amounts: iron, 
manganese, copper, zinc, boron, chlorine and molybdenum. They are 
equally essential for the nutrition of livestock and people. Plants 
normally obtain them from the soil. We and other animals get them 
from plants.

Sodium is found in almost all plants but apparently is not necessary for 
their growth except where potassium is lacking. It is indispensable to 
animals and we provide it in sodium chloride -- common salt. Large 
quantities of aluminum and silicon are present in most soils and are 
concentrated in some plants. The straw of cereals such as wheat, and the 
stinging hairs on nettles, are stiffened with silica. Otherwise, if plants 
need aluminum and silicon at all it must be in small quantities.

Cobalt, iodine, fluorine and vanadium, although apparently of no 
benefit to green plants, are classified now as micronutrients because, in 
tiny amounts, they have been proven essential for animals. Cattle and 
sheep, grazing luxuriant plants on land seriously deficient in cobalt, 
waste away and die unless the soil is treated with small amounts of 
cobalt salts. Similarly, an iodine deficiency causes goiter in man and 
other mammals because that element is needed to stimulate the thyroid 
gland Fluorine is necessary for the development and health of bones 
and teeth.

You may have heard or read about "trace elements" in soils, a popular 
name for micronutrients. Scientists now restrict that term to soil 
minerals which have not been found important for the nutrition of either 
plants or animals -- elements such as selenium, nickel, gallium, 
columbium, tin and tungsten.

Selenium is most notorious and troublesome. It is a hazard to livestock 
where some soils, in a semiarid belt extending from Canada to Mexico, 
contain concentrations of this sulfur-like mineral. Certain forage plants 
absorb enough of it so that browsing animals are seriously affected and 
frequently die.

On the other hand, some soils are so deficient in micronutrients such as 
zinc, boron and molybdenum that, unless treated with small amounts of 
those minerals, plants and especially animals which eat them become 
diseased.

Land which has been robbed of its fertility by over-cropping, without 
any applications of fertilizers, may be seriously deficient in phosphorus, 
potassium, calcium, sulfur and magnesium.

A bunch of carrots, grown on such soils, may not have much more food 
value than a toothpick.