Lime, to use the popular term, is a most important ingredient in soils, and may be employed in various forms, such as marl, gypsum, quicklime, chalk, slaked lime, gas lime (or " blue billy "). For a heavy, wet, clayey soil a heavy dressing of quicklime is one of the ways of bringing it into a good state of cultivation. In milder forms of chalk (carbonate of lime) or gypsum (plaster of Paris) it is a valuable adjunct to good garden soils, especially if they have been overdressed with organic manures.

The advantages of adding lime to the soil may be summed up as follows: -

1. It makes a stiff or clayey soil drier and more porous by making the sticky particles coagulate or flocculate, and thus leave passages for the air. This may be proved by putting a little lime into a glass of muddy water. The particles that would otherwise float about for a long time soon come together in flocks and drop to the bottom, leaving the water clear.

2. Lime, being an alkali, is fatal to sourness and acidity in the soil, and renders it "sweet" and favourable to vegetation. Where magnesia is in excess the addition of lime will rectify any ill effects.

3. Without the presence of lime in the soil beneficial micro-organisms would not be generated from the organic constituents, and there would be a lack of nitrogenous food. On the other hand, when a soil has become too rich in nitrogenous foods, that cause luxuriant, sappy, and unproductive growths, the addition of lime will soon restore the balance, although at first giving apparently greater vigour to the shoots.

The presence of lime in any soil may be detected in a simple way. Take a fair sample and place in a glass, and pour over it some fairly strong acid, such as hydrochloric. If lime is present a vigorous fizzing or effervescence will take place; if not, it may be assumed that little or no lime is present and it should be added.