Biologically lime aids the process of nitrification.
The action of lime is greatest in its caustic or unslacked form.
Too much or too frequent liming may injure the soil. It should be carefully tried in a small way, and its action noted, before using it extensively.
A common way of using lime is to place twenty to forty bushels on an acre in heaps of three to five bushels, covering them with soil until the lime slacks to a fine powder. The lime is then spread and harrowed in. Lime tends to hasten the decay of humus. It should not be applied oftener than once in four or five years.
Gypsum, a sulphate of lime, is similar to lime in its action on the soil. Its most important effect is the setting free of potash from its compounds.
Gas lime should be used with great care as it contains substances that are poisonous to plant roots. It is best to let it lie exposed to the weather several months before using.
Marl is simply soil containing an amount of lime varying from five to fifty per cent. It has value in the vicinity of marl beds but does not pay to haul very far.