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.