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In a natural state it is obtained from bones, guano and wood ashes; and in an artificial condition from basic slag or Thomas’s phosphate, coprolites and superphosphate of lime.

Manuring with basic slag at the rate of from 5 to 10 cwt. per acre has been found to give excellent results on poor clays and peaty soils.

If basic slag and kainit are given, autumn is the time, as their action is slow.

This is the case, indeed, with many artificial manures, such as guano, bones, nitrate of soda, and basic slag.

The amount of effective lime in basic slag, as made by modern methods, is so small that its value is nearly negligible.