A crumbly mixture of clays, calcium, magnesium carbonates, and remnants of shells that are sometimes found under desert sands and used as fertilizer for soils that are lacking in lime: Marl is a part of the earth's surface that contains humus and disintegrated rock which is used to increase the necessary lime content in some farmland areas.

There are soil experts who believe that marl is a valuable fertilizing material for various kinds of soils depending on their compositions.

To overspread or to fertilize soil with a mixture of clay, sand, and limestone in varying amounts: The farmers were marling their farmland with the soft and crumbly earth deposits so they could improve the acidity of their soils.