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Acid Phosphate

Categories: COMMERCIAL SOURCES OF PLANT-FOOD

When animal bone is treated with sulphuric acid, the

result is an acid phosphate, but treated animal bone is so rare on the

market that it may be ignored. The acid phosphate on the market is

rock-phosphate treated with sulphuric acid to render its plant-food

available. The content of phosphoric acid varies because the original

rock-phosphate varies, but the most common grade on the market is

guaranteed to contain 14 pe
cent available phosphoric acid, and 1 to 2

per cent insoluble. Some acid phosphate is guaranteed to contain 16 per

cent available phosphoric acid, and some runs down to 10 per cent

available.



An acid phosphate contains quickly available plant-food. A prejudice

exists against it on account of its source, and it has been a common

practice to label the bags "bone-phosphate," or "dissolved bone," or

such other designation as would imply an organic source, but the acid

phosphate is made out of rock-phosphate, regardless of the name given.

The prejudice against the rock as a source of plant-food is giving way.

It is our chief and cheapest source of supply. The combination of

sulphuric acid with rock-phosphate in the production of acid phosphate

produces sulphate of lime, known as gypsum or land-plaster. The amount

of gypsum in a ton of acid phosphate varies, but may be roughly

estimated by the buyer as two thirds of the total weight of the acid

phosphate.



The tendency of gypsum is, in the long run, to make a soil acid, and

its use necessarily hastens rather than retards the day when a lime

deficiency will occur. The influence in this direction is not great

enough to be a very material factor in deciding upon a carrier of

phosphoric acid. If a soil has little lime in it, a state of acidity

soon will come anyway, and the increase in amount of required lime will

be small. The cheapness of acid phosphate, as compared with animal

bone, is the decisive factor.



The ill-effects usually attributed to acid phosphate are not due in any

great degree directly to the sulphuric acid used in its making, but to

the bad farming methods that so often attend its use. When the need of

commercial fertilizers is first recognized, acid phosphate seems to

meet the need. The soil's store of available phosphoric acid gives out

first, and this fertilizer brings a new supply. If the available potash

is in scant amount, the acid phosphate helps in this direction by

freeing some potash. The phosphoric acid has peculiar ability in giving

impetus to the growth of a young plant, and that enables it to send its

roots out and obtain more nitrogen than it otherwise would do. The

farmer thus may come to regard it as a means of securing a crop, and

there is neglect of manure and clover. If a field is thin and fails to

make a sod, there is no immediate compulsion to use manure or to grow a

catch crop to get organic matter, but the field is cropped again with

grain. Soon the supply of humus is exhausted, the soil lies lifeless,

and the stores of available nitrogen and potash are in a worse depleted

state than formerly.



The fault lies with the method. The phosphoric acid in the acid

phosphate was needed. Profit from its use was legitimate, but the

necessity of supplying organic matter became even greater than it would

have been otherwise. Tens of thousands of our most successful farmers

use heavy applications of acid phosphate, but they keep their soils in

good physical condition by the use of manure or clover, and they apply

potash and nitrogen when needed. The clover is assured by using lime

wherever it is in too limited supply, and that is the case in most

instances, regardless of the use of any kind of commercial fertilizer.



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