Man's physical universe

xanabras

FOODS 731

roots by dialysis.

The weathering of rocks, freezing and thawing, action

of acids from decaying plants, action of carbon dioxide and other gases

in the air, and many other processes are constantly changing insoluble

minerals into soluble forms. Often these processes do not keep up with

the plant requirement, and the soil becomes depleted. At other times,

soluble salts are formed more rapidly than drainage or plant growth can

remove them, and they accumulate, producing "alkaline" soils. Extensive

experimentation has shown that plants differ very much in

their mineral requirements. Some plants will thrive only in acid soils,

while others grow best in basic or saline soils. The scientific agriculturalist

must first obtain analyses of the soils that he has to work

with and then either add chemicals to change the composition of the

soils to satisfy the requirements of certain plants or select plants which

are adapted for growth in the soils available.

Analysis is, therefore, just

as important in agriculture as it is in industry; in each case the nature

of the final products is determined by the nature of the raw materials.

The majority of experiments with soil-less growth of plants by

amateurs have failed because the proper mineral concentrations for

particular plants have not been provided. There is no one mixture of

salts that is best suited to all plants. Another reason why such experiments

fail is that there are no means available to amateurs to analyze

the nutrient solutions frequently in order to maintain the proper concentration.

The growth of plants in nutrient solutions is like the raising of children;

the food needs change as the plant develops.

Fertilizers Are Added to Soils to Provide Mineral Deficiencies.

Analysis will show that certain soils are deficient in certain elements

at the start.

In most cases plants remove essential minerals from the

soil to an extent that the soil will gradually lose its fertility unless these

minerals are returned to the soil. A fertilizer is simply a salt or mixture

of salts which contains the elements which must be added to the soil to

provide the proper balance of minerals for the plants which are to be

grown in the soil. It is obvious that the composition and amount of a

fertilizer needed for a given soil can be determined only on the basis of

a soil analysis and an expert knowledge of the mineral requirements of

the plants which are to be grown in the soil.

Fertilizers Make Possible Greatly Increased Crop Production.

When it is considered that 25 bushels of corn will remove 39.2 pounds

of nitrogen, 13.8 pounds of phosphoric acid, and 27.6 pounds of potash,

it is easy to understand why soils will lose their fertility unless these

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