Odds are good farmers may never see evidence of calcium deficiency in their crops.
The most common and least chemically mobile of the secondary nutrients, calcium is essential for cell wall construction in plants and allows plant cells in young crops to divide normally. Calcium also helps plants metabolize nitrogen, which most growers are probably intimately familiar with. Deficiencies — when they can be found — prevent young plants from progressing normally.
However, calcium is so abundant that examples are few and far in between, says Ray Ward, owner of Kearney, Neb., -based Ward Laboratories.
“I’ve tested plants for 60 years, and I’ve never seen a case of calcium deficiency,” he says.
How It Behaves. Calcium sticks around.
It’s the most common positively charged ion in soil clay and organic matter because it clings more tightly to the surface of clay particles than other common positive ions like magnesium or potassium. It’s found in soil minerals like amphibole, apatite, calcite, dolomite, feldspar, gypsum and pyroxene, according to publications issued by the University of Wisconsin Agricultural Extension.
The materials that soil is made from also tend to contain lots of calcium, making the risk of running out relatively rare. Calcium is also held more tightly than either magnesium or potassium.
Inside the plant, calcium only moves via water running from the roots up to the leaves.
Calcium deficiency tends to show up in younger plants. Bud tips and root tips fail to develop. For example, in corn, leaf tips stick together and prevent new leaves from unfolding. The condition is known as “buggy whipping,” though it’s more often caused by herbicide injury and environmental stress than calcium deficiency.
Calcium concentrations increase as the plant ages, so growers seeking to test for calcium should indicate the plant’s growth stage when collecting plants for testing. For example, sampling alfalfa during budding should yield a sufficient level of 1.1-2%.
The Benchmark. The ideal levels of calcium in soil are 400-600 parts per million for sandy soils and 600-1,000 parts per million for other types of soils.
Soils with low concentrations of calcium frequently have low pH and require liming, though repeated applications of potassium on sandy soils can sometimes result in neutral soils with relatively low calcium levels.
Limestone — frequently used to address pH issues in soil — contains calcium, though the amount of calcium different varieties of limestone contain can vary by state. In particular, dolomitic limestone has a calcium to magnesium ratio of about 2:1, which is within the range for normal crop growth. Dolomitic lime also has the benefit of being less expensive than other sources of calcium.
Calcium deficiency can also sometimes appear in acidic soils with a pH below 5.0 that also lack organic matter.
How To Apply. Given calcium’s staying power and prevalence, most literature doesn’t recommend additional applications outside of regularly scheduled limings.
“The amount of calcium normally added in limestone applications, combined with the relatively large amounts of exchangeable calcium … far exceeds the 250-100 (pound per acre) annually removed by crops,” the publication Soil and Applied Calcium reads in part.
If calcium lime deficiency is correctly diagnosed, calcitic lime and dolomitic lime contain enough calcium to address the process. Slaked lime contains about 54% calcium by volume. Calcitic lime is 40% calcium by volume, and papermill lime sludge contains about 38% calcium by volume, while dolomitic lime and gypsum each contain about 22%. Gypsum isn’t recommended except for specific circumstances where soil has a low-cation exchange rate and the planted crops require acidic soil.
The Payoff. While calcium deficiency might fall under the category of least concern for most crops, individual crops may benefit from some calcium application. These include potatoes, particularly in situations where potash or other potassium applications have been made in the past, and apples grown in high-pH sandy soils.
“High rates of potash applied to potatoes depress calcium uptake,” the publication reads in part. “The additional calcium improves resistance to bacterial soft rot and internal brown spot and consistently improves potato grade.”