The Push for Higher Soil Calcium Levels

Calcium, like most recognized soil nutrients, plays a large role in overall plant success. It is the foundation of cell walls, promotes root growth, acts as the plant’s defense, and helps manage stress. This macronutrient is readily available in most Midwest soils, however, there has been a movement to increase the soil calcium levels regardless of soil test levels. Have you ever experienced calcium deficiency?

Having adequate calcium levels is necessary for the most productive crop, but what happens when soil levels are excessive? The goal of increasing soil calcium levels is to remove magnesium from the soil colloid in hopes to maximize flocculation. Flocculation is when clay particles clump together forming aggregates, or larger clusters of soil particles. Calcium binds to the soil colloid stronger than magnesium and can form larger aggregates such as blocky formations. This is crucial for water drainage, root penetration and pore space but creating excessive soil calcium nutrient levels is unnecessary.

What is the correct calcium to magnesium ratios and levels? When discussing these two ranges of sufficiency levels, it is entirely dependent on soil type, parent material and region. The parent material, or the original base layer of the soil, is constantly being weathered and breaking down. This releases nutrients such as magnesium depending on the type of parent material. When examining soil test results, a 1:1 ratio of calcium to magnesium involves alternate management decisions. This is often switching from dolomitic limestone, which consists of about 11% magnesium and 21% calcium, to a high calcium lime like calcitic limestone, which contains about 40% calcium and .2% magnesium.

In The Great Lakes Region, higher magnesium to calcium ratios is not unheard of but exist in certain concentrated areas. These areas usually have a lighter CEC, or cation exchange capacity. This creates another challenge for applications and rates. If the CEC is low, there are fewer exchange sites on the soil colloid. Once a high calcium lime is spread, it can dramatically reduce the number of other cations on the colloid. Other cations, such as magnesium and potassium, are then leached away with calcium remaining on the exchange site. Magnesium is the center of chlorophyll. The main energy source for all living plants. Negative impacts of high application rates can reduce yields at a much greater rate than trying to achieve a better calcium to magnesium ratio.

Before making a management decision, there are some questions to answer with appropriate responses. Is the soil pH where it needs to be? Are calcium and magnesium in the sufficient range? What is the CEC? How many sampling events are providing this data, and are the levels consistent? It is recommended to not apply more than 2.5 tons of liming material in one application for most soil, and 2 tons for soils with lower CEC.