Testing soil every two years and applying frequent small amounts of lime can help farmers avoid the creation of an alkaline layer at the soil surface. That’s especially important in no-till operations.
This little-understood nutrient holds the key to soil health, which lays the foundation for high yield
It’s common knowledge that limestone applications are necessary to prevent soil from becoming acid. But how does that process work? If you understand it, your lime applications will become more effective.
The liming process revolves around calcium, as Farm Journal Field Agronomist Ken Ferrie has explained at several sessions of Farm Journal Corn College. Calcium, like sulfur, is considered a secondary nutrient—falling between the primary nutrients (nitrogen, phosphorus and potassium) and the micronutrients.
Calcium is vital in plants as well as in the soil. In plants, it helps regulate osmotic pressure, which affects drought tolerance, and blocks the accumulation of toxic amounts of manganese in plants. That is why symptoms of calcium deficiency are essentially the same as those of manganese toxicity.
"Calcium deficiency in plants is rare," Ferrie says. "It’s calcium’s role in the soil, in regulating acidity, or pH, that farmers need to be concerned with."
In the soil, calcium holds the key to healthy structure, Ferrie continues. That’s because a calcium ion has two valence electrons, or positive charges. Such an ion is called a cation (pronounced "cat-ion").
Bridging clay particles. One of the calcium ion’s positive charges attaches to a clay particle, which has a negative charge. The second positive charge "captures" another clay particle. "This is called flocculation—bringing clay particles together, yet keeping them apart," Ferrie says. "It’s like building a bridge."
Secretions from the roots of grass plants (corn, wheat and rye, but not soybeans, tobacco or cotton), help glue the floccu-lated clay particles together, capturing sand and silt particles in the process. This forms soil aggregates, creating a healthy, crumblike soil structure.
"Large pore spaces, called macropores, around the soil aggregates serve to house the ‘soil solution,’" Ferrie says. "This is where nutrient exchange takes place between microorganisms in the soil and where root growth occurs."
In other words, without calcium, soil won’t have those essential macropores. But the bridges between clay particles can be broken, by heavy implements, tillage or by displacement of the calcium ions.
"Calcium ions can be displaced by single-valent salts such as sodium," Ferrie says. "Displacement can be caused by high salt loads in irrigation water on poorly drained soils. In the Middle East, areas that once were productive deltas under irrigation are now deserts because of poor drainage and salt buildup. Displacement can also result from overapplying manure, which can be high in salt.
"We fix this problem by installing drainage or applying a product such as gypsum [calcium sulfate]. The sulfate marries up with the salt, rainwater flushes it out and calcium rebuilds the soil bridges."
Creating acidity. A more common problem occurs when we replace calcium ions with hydrogen ions. "Hydrogen is a waste product of plant growth and soil microbes," Ferrie says. "It also comes from most nitrogen fertilizers, and from acid rain."
Excess hydrogen ions create soil acidity, which we measure as pH—0 to 6 being acidic, 7 being neutral and 8 to 14 being alkaline.
You can think of acidity this way: Battery acid is 0, pure water is 7 and bleach is 14. The pH scale is logarithmic, so a pH of 6.0 is 10 times more acidic than a pH of 7.0.
- Mid-February 2012