Got Calcium?

By Nina Prater, NCAT Southeast and Appalachia Regional Coordinator

Calcium might not have as good a publicist as the Big Three soil nutrients—nitrogen (N), phosphorus (P), and potassium (K)—but even though we don’t hear about it as much, it still is a critical plant nutrient that is essential for soil health. Early soil health pioneer Sir William Albrecht even called it the “premier” soil nutrient! It is not only important for plant health but also has a big influence on soil pH. Lee Rinehart, Darron Gaus, and I wanted to give calcium the attention it deserves, so we got together to record a podcast about soil calcium and how to manage it sustainably.

Not all soils are created equal when it comes to calcium management. In acidic, low pH soils, agricultural lime—aka calcium carbonate (CaCO3)—is commonly used to increase the pH to that target sweet spot of 6 to 7.5 (for most crops). In alkaline, high pH soils, gypsum (CaSO4·2H2O) is used as a calcium source, as it increases calcium without raising the soil pH even further.

Where Darron lives in Austin, Texas, the dry climate has allowed calcium to accumulate in the soils over millennia, creating an over-abundance of the nutrient (though, as you’ll hear in the podcast, it’s not always plant-available even there!). In Arkansas where I live, the relatively humid and rainy climate has resulted in acidic soils low in calcium because calcium is soluble and can wash away. Where Lee lives in Pennsylvania, he is surrounded by some of the best soil in the world. He’s the “just right” in this Goldilocks story with good calcium, organic matter, and pH levels. These three examples illustrate how varied soils can be when it comes to calcium, and that will result in a wide range of management strategies to make sure your soils and plants are getting what they need.

A key point that came out of our conversation was that no matter what the native soil is, and no matter what nutrient you’re looking at, having healthy soil that you nurture with cover crops, biodiverse plants, organic matter inputs, and mulch or living roots for protection is essential to sustainable nutrient management. You can reduce the need for off-farm inputs if you treat your soil like the living ecosystem that it is.

If you want to go back and listen to our episodes on nitrogen, phosphorus, and potassium, you can find those linked below. We are planning to work our way through the soil macro- and micronutrients one episode at a time, so stay tuned to learn all about magnesium, sulfur, and more. We’ll do our best to make even boron not boring.

Related ATTRA Resources:

Episode 164. Soil Sessions: Understanding Soil pH

Episode 260. Rising Fertilizer Costs: Look to History for Answers

Episode 304. Phosphorus and the Beauty of Biology

Episode 323. Potassium from Past to Present

This blog is produced by the National Center for Appropriate Technology through the ATTRA Sustainable Agriculture program, under a cooperative agreement with USDA Rural Development. ATTRA.NCAT.ORG.