Writing yesterday’s post on soil horizons, I ran across a couple of unfamiliar words. Marl was one of them. Here’s what I’ve learned about marl.
The word marl comes to us from the late 19th century. It is short for marbled. Rather than being as hard as your favorite cat’s eye or aggie marble, marl is a porous, relatively soft mudstone. And it contains many of the nutrients your plants love.
The lower cliffs of Dover and much of New Jersey contain marl.
Marl forms as carbonate-rich clay mud and silt are blended with algae that loves alkaline waters. The carbonate is from the dead shells of water-dwelling organisms and the calcified algae. Originally the term marl only referred to freshwater formations. We now know that marl occurs in saltwater too.
Types of marl
Marl contains 65–35% carbonate and 35–65% clay, depending on the type. It can be blue, green, sand-colored, or red. Marl contains calcium, iron, phosphorus, potash, silicic acid, and sulfur. It also contains magnesium, but only a little. Magnesium deficiencies are common in fields treated with marl.
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