Marl

• Marl is a calcium carbonate, clay-like, finely textured soil. Crops such as sweet corn and potatoes thrive on it. It has very high pH levels. Sticky in texture and whitish in appearance, marl is usually found near marshlands. Marl formed many millennia ago when chara, an aquatic plant, extracted calcium carbonate from melting glaciers, storing it in its branches. Dead plants sank to the bottom of the lake, over time forming the marl. Peat also forms from decayed plant matter, but later in time than marl. Peat deposits only have marl underneath.
  
  

History

• Rock materials such as marl have been used as an aid to soil fertilization since time immemorial. According to Pliny the Elder, the Germanic tribes introduced the use of marl as fertilizer to the Romans. By the 18th century, agricultural development and marl deposits were synonymous. However, as noted by the International Union of Soil Sciences, "Marl was known in the 18th century as a agent to make fathers rich and grandsons poor," as long-term over-reliance on marl as fertilizer eventually depleted lesser soils that originally did well when marl was added.
  
  

Fertilizer

• In time past, farmers used marl to fertilize soils low in lime, and also to condition sandy soils for planting. Marl's lime content joins sand grains, to aid in heat and water retention. For clay, the opposite is true, as marl allows clay soil particles to loosen, letting water permeate and air and heat to circulate. Our farming ancestors sought out areas with marl deposits when settling in North America, as they realized the importance of marl to soil fertility. In the pre-industrial area, transporting marl was difficult, if not impossible.
  
  

Marl Use Today

• Rock powders such as marl became easily and transportable available as by-products of the today's modern economies based on fossil fuels. These materials are still in use for soil fertility management, and marketed by agricultural fertilizer producers. Before applying marl, the farmer must take into account the acidic quality of the soil and the overall soil content. Marl's long history as a fertilizer makes it especially useful for long-term soil management, as both its positive and negative effects are well-known to agronomists.