My soil calcium levels are high. What can I do? (ASK Advice)

While many SoilKit customers are concerned about nutrient deficiencies in their soil, one of the most common questions we get is actually about an excess of a particular nutrient: calcium. What causes this issue, and what can you do to address it?

There are several potential factors that can contribute to high soil calcium levels:

• Parent material. Some soils naturally have high calcium content due to the source material they were formed from, such as limestone.
• Soil amendments such as lime and gypsum. Chemically speaking, lime is primarily calcium carbonate and gypsum is calcium sulfate dihydrate -- both calcium-containing molecules. There's even a nitrogen fertilizer that also adds calcium to the soil (calcium nitrate), and large compost additions can also contribute excessive amounts of calcium in some cases.
• Irrigation water. Depending on your local area, the water you use for irrigation may be "hard water" with high calcium levels.

The steps you might take to manage or prevent high calcium levels and associated issues will depend on your situation and the specific issues you're trying to address alongside high calcium.

• Is your pH too high? Since soil calcium is often in the form of lime (calcium cabonate), it's often associate with alkalinity and high pH levels. Alkaline soils are typically managed by adding sulfur compounds to meet the pH needs of the plants you intend to grow. This is a gradual, multi-year process requires that patience, as the sulfur and caclium first react with eachother, neutralizing each other, before sulfur addition can really add acidity to the soil. Because of this, alkaline soils with high calcium levels are poorly suited to growing acid-loving plants, such as blueberries. 
• Are you already regularly irrigating? Advice for a rain-fed system may indicate to use water to flush excess calcium and/or other salts from the soil. However, if you regularly water your lawn or other managed area, the irrigation water itself could be introducing more calcium to the soil! In lawns, hard water can cause chlorosis (yellowing) due to high calcium and/or magnesium levels. One alternative is to set up a rain barrel and collect fresh water for your lawn since rain is low in minerals. In extreme cases, some people install a water softener to remove calcium from their irrigation water, but this should be done with care since some water softeners can add sodium to the water and ultimately damage your soil.
• Are you trying to fix poor structure/high dispersion? These are common symptoms of sodic soils, which are defined as soils high in sodium (Na) but low in overall salt content. Sodic soils are typically remediated with gypsum, since adding calcium displaces the sodium and helps it leach out of the soil. However, if you're experiencing high sodium AND high calcium levels, you are dealing with a saline-sodic soil, which should not be treated with gypsum! Adding more calcium won't improve a situation where it's already present in high amounts. It's important to note that gypsum is not a cure-all for dispersive soils, especially sandy soils that don't naturally have strong structure.
• Is your soil deficient in other nutrients? You can select fertilizers and amendments to address these issues by avoiding those that contain unneeded calcium. For example, if you have raised beds that are high in calcium and other nutrients but low in one specific thing, you may prefer to ammend with a synthetic fertilizer for the deficient nutrient rather than a rich compost that will introduce calcium and many other nutrients in excess of your soil's needs. Save the compost for another area of your yard that needs more attention!

At the end of the day, high soil calcium is something to be aware of and take into account since it's often an impossible situation to reverse. By taking steps to address the symptoms that arise and to avoid exacerbating the issue, you can still have a healthy lawn and a productive garden, despite over abundant calcium levels.