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Basic Slag

Categories: COMMERCIAL SOURCES OF PLANT-FOOD

When iron ores contain much phosphorus, its extraction by

use of lime gives a by-product in the making of steel that has

agricultural value. The ores of the United States usually do not give a

slag sufficiently rich in phosphorus to be valuable. Nearly all the

basic slag used as a fertilizer is imported from Germany, and usually

contains 17 to 18 per cent of phosphoric acid. The availability of the

plant-food in this f
rtilizer has been the subject of much discussion.

The chemist's test which is fair for acid phosphate is admittedly not

fair when used for basic slag. Field tests, at experiment stations and

on farms, are our best sources of knowledge. When the soil is slightly

acid, each 1 per cent of phosphoric acid in the slag appears to be

about as valuable as each 1 per cent of the available phosphoric acid

in an acid phosphate. Some of the effectiveness may be due to the lime,

although very little of it is in forms regarded as valuable for the

correction of soil acidity. There is evidence that basic slag favors

clover. It has not been found feasible to ship this material many

hundreds of miles inland from the seaboard to compete with acid

phosphate, but it is an excellent source of phosphoric acid for soils

that are not rich in lime.



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