Dolomite is a naturally occurring mineral that contains significant amounts of calcium and magnesium. It has become a popular fertilizer in gardening and agriculture to provide plants with these essential nutrients. This article will explore the benefits of utilizing dolomite as a fertilizer, how to properly apply it, and some important considerations when using dolomite.

The Origin and Composition of Dolomite

Dolomite forms naturally when magnesium ions replace some of the calcium ions in calcite limestone. This geological process happens over millennia as water percolates through rock, gradually transforming it into dolomite mineral deposits.

Dolomite contains approximately equal parts magnesium carbonate and calcium carbonate. Pure dolomite is expressed as CaMg(CO3)2. However, most commercial dolomite used in agriculture contains small amounts of other minerals like silica, iron, aluminum, and manganese.

Different sources of dolomite have slightly varied compositions. Dolomite from inland ancient sea beds tends to be harder and richer in magnesium compared to more porous and calcium- predominant marine dolomite deposits. Testing can determine the exact make-up of a dolomite product.

The Benefits of Dolomite Fertilizer

Providing calcium and magnesium to plants is crucial for healthy growth and development. Calcium helps strengthen cell walls and improves overall plant vigor. It also aids in the uptake of important nutrients. Magnesium is a core component of chlorophyll, so it supports photosynthesis. Without adequate magnesium, plants can experience interveinal chlorosis, where the tissue between veins turns yellow while the veins remain green.

Dolomite contains high levels of both calcium and magnesium, making it an excellent fertilizer to meet plants’ needs. The optimum Ca:Mg ratio is around 6:1, which dolomite provides. In contrast, calcitic limestone only contains calcium. The magnesium in dolomite can help correct magnesium deficiencies.

Dolomite also gradually raises pH levels in soil over time as it dissolves. This can help make soil less acidic and more hospitable for plants that prefer neutral or slightly alkaline soils. The mineral ions in dolomite also displace hydrogen ions, further reducing acidity.

Deciding Between Dolomite and Limestone

While both dolomite and limestone contain calcium and can raise pH, they differ in a few key ways. As described above, dolomite also provides magnesium. Meanwhile, limestone is quicker acting and can more dramatically shift pH in a short period.

Here are some guidelines for choosing between dolomite and limestone:

  • Use dolomite when soil tests show a need for magnesium in addition to calcium.
  • Choose dolomite for a slower, steady pH increase over several seasons.
  • Limestone is preferable for making rapid pH adjustments.
  • Use limestone if magnesium levels are already sufficient.
  • Combine limestone and dolomite applications for a blended calcium-magnesium benefit.

When in doubt, have soil tested and consult with farming or gardening experts to decide which amendment best suits your needs.

The Difference Between Dolomite and Gypsum

While dolomite (CaMg(CO3)2) and gypsum (CaSO4·2H2O) are somewhat similar soil amendments, they have several key differences.

Dolomite contains calcium and magnesium, while gypsum provides only calcium. Dolomite is slower to dissolve and raise pH compared to gypsum.

Additionally, gypsum adds calcium without altering pH levels. It can even help reclaim sodic soils high in sodium. Meanwhile, pH neutral gypsum has no effect on acidic soils.

Gypsum contains sulfur which dolomite does not provide. The sulfur bolsters plant growth and aids in pest and disease resistance.

Finally, gypsum is more water soluble and immediately usable by plants. Dolomite takes time to breakdown and release its nutrients.

Application Rates and Timing

Most experts recommend applying dolomite at rates between 1-3 tons per acre. Organic agriculture guidelines suggest using a dolomite powder ultrafine grade for optimal absorption. Re-apply dolomite every 2-3 years to maintain sufficient calcium and magnesium levels.

As mentioned previously, applying dolomite well ahead of planting allows it time to fully interact with soil. Early fall is ideal timing, as winter precipitation helps dissolve and spread dolomite through the soil profile before the next growing season.

With its steady release of calcium, magnesium, and pH-moderating power, dolomite is a safe way to build fertile, mineral-rich soil for gardening and farming. When used properly, it can provide lasting benefits for soil health and plant productivity.

The Impact of Dolomite on Soil Biology

In addition to providing calcium and magnesium, dolomite also benefits soil life and ecology. The mineral ions released during its gradual dissolution help feed soil microorganisms and facilitate biochemical reactions.

Dolomite raises pH levels, which in turn encourages microbial activity and breakdown of organic matter. This liberates even more plant-available nutrients. The microbes also associate symbiotically with plant roots, enhancing nutrient uptake.

Additionally, dolomite provides habitat for worms and beneficial insects that burrow and tunnel through the soil. Worm castings further boost nutrient content in the root zone. By supporting soil biology, dolomite improves fertility and plant growth.

Important Considerations When Using Dolomite

While dolomite offers substantial benefits, there are a few important caveats:

  • Only use dolomite if soil tests confirm a need for calcium and magnesium. Excessive amounts can harm plants.
  • Dolomite raises pH slowly over time. It’s not a good option for quickly altering overly acidic soils. Use limestone instead.
  • Thoroughly mix in dolomite rather than letting it sit on top of soil. Direct contact can burn roots.
  • Avoid using dolomite for plants that prefer acidic soils like blueberries and azaleas. It may harm them.
  • Be aware that dolomite can cause salt buildup if used excessively or on plants sensitive to salt.
  • Dolomite may contain small amounts of lead, so don’t use it for root crops or vegetables.

Considerations for Organic Agriculture

Dolomite is generally allowed in organic farming, but there are some important considerations:

  • Check that the dolomite source complies with USDA National Organic Program standards. Some dolomite contains prohibited synthetic processing aids.
  • Avoid dolomite contaminated with lead or other heavy metals. This can disqualify crops from organic certification.
  • Apply dolomite conservatively to meet – but not dramatically exceed – soil test recommendations.
  • Combine with organic compost, manure, and cover crops to balance the mineralization from dolomite with organic matter for living soil.

With care taken to find a high-quality product, dolomite can provide a plant-based, slow-release source of calcium and magnesium suitable for organic farms and gardens.