Understanding Plant Nutrition: Limestone, Calcium And Magnesium

Understanding Plant Nutrition: Limestone, Calcium And Magnesium

The reason for adding limestone to a container media, besides pH control, is to supply calcium and, depending on the limestone, magnesium. In this article, we will discuss the nutrient content of different types of limestone and how limestone influences calcium and magnesium nutrition. 

Limestone Nutrient Content

There are four types of carbonate-based limestone that are available. Calcite is pure calcium carbonate (CaCO3, 40 percent Ca). Calcitic lime is composed of mostly CaCO3 (> 30 percent Ca) with some MgCO3 (<5 percent Mg). Dolomitic lime contains less CaCO3 (<30 percent Ca) and more MgCO3 (>5 percent) than calcitic lime. Finally, dolomite also contains CaCO3 and MgCO3, but at a specific ratio of 22 percent Ca to 13 percent Mg.

Calcium hydroxide (Ca(OH)2), also known as hydrated lime, or calcium magnesium hydroxide (CaMg(OH)4), also known as dolomitic hydrated lime, are sometimes used as a fast reacting liming source because they will react quickly and leave no residual. Calcium hydroxide contains approximately 54 percent Ca, while calcium magnesium hydroxide contains about 30 percent Ca and 18 percent Mg.

Sometimes the calcium and magnesium content of the limestone is listed as CaO or MgO on the label. To convert CaO to actual Ca, multiply the CaO value by 0.71. To convert MgO to actual Mg, multiply the MgO value by 0.6. 

Reactive Lime And Calcium

Reactive lime is that fraction of the incorporated limestone that causes the media pH to increase initially after mixing. When limestone is incorporated into a media, the important reactions that occur are:

2peat-H <—> 2peat- + 2H+

2

CaCO3 + 2H+ <—> Ca2+ + H2O(water) + CO2 (gas)

3

Ca2+ + 2peat- <—> Ca-peat2

After the peat and lime are done reacting and the equilibrium pH is reached, the peat is less acidic and contains calcium on its exchange sites. When limestone is suggested as a source of calcium for the plant, it is usually the exchangeable calcium left over from the reactive lime fraction.

Research at Michigan State University tested the effect that a dolomitic limestone had on pH and calcium concentrations for the first four weeks after mixing (Figure 1). It was shown that the reactive fraction of the limestone had little effect on root-medium calcium concentrations, even as the limestone continued to react.

It appears that once the calcium from the reactive limestone is bound to the peat, it is not released back into the soil solution under most conditions. Since nutrients must be soluble to be taken up by the plant, the bound calcium does not influence calcium nutrition, either in the short term (mixing to stable pH) or the long term (stable pH till the end of the crop). It also may explain the reason that cation exchange capacity of a limed peat has minimal influence on pH buffering. 

Residual Lime And Calcium

Just like with pH buffering, it’s the residual lime fraction that influences calcium buffering. Figures 2 and 3 show the results from an experiment at Michigan State University in which the same peat/perlite media was prepared using two different types of lime. The low-residual treatment contained a hydrated lime, which reacted quickly and completely, leaving no residual. The high-residual lime treatment contained a dolomitic lime with a large residual fraction. Impatiens were grown for 17 weeks in both media using one of three fertilizer solutions.

The acidic nutrient solution (NS) was composed of water with 20 ppm alkalinity and a fertilizer containing 50 percent NH4-N:50 percent NO3-N. The neutral NS was composed of water with 120 ppm alkalinity and a fertilizer containing 25 percent NH4-N:75 percent NO3-N. The basic NS was composed of water with 120 ppm alkalinity and a fertilizer with 3 percent NH4-N:97 percent NO3-N. The calcium concentrations also differed between the fertilizer solutions with the acidic NS containing 15 ppm Ca, the neutral NS containing 50 ppm Ca and the basic NS containing 150 ppm Ca.

When the acidic NS was used, both media and shoot-tissue calcium concentrations were significantly higher in plants grown in media containing the high residual lime fraction compared to those grown in the media without the residual lime (Figures 2 and 3).

However, when less acidic fertilizer solutions were used, there was little difference in the media or shoot-tissue calcium concentrations of plants grown in the two media.

These results suggest that the residual lime contained in the medium after the equilibrium pH was reached did not, in itself, buffer the root-medium Ca concentrations. Instead, the increase in root-medium and shoot-tissue Ca resulted from the reaction of the acidic NS with the residual lime. Decreasing the acidity of the fertilizer solution, either by reducing the amount of NH4-N in the fertilizer or by increasing the alkalinity of the water, almost completely negated the residual lime as a calcium source. 

Magnesium

The effect that limestone has with magnesium nutrition follows the same pattern as with calcium.

The reactive lime fraction did not influence magnesium concentrations in the media, even as the limestone continued to react. While the residual lime fraction was a source of magnesium under acidic conditions, reducing the acidity of the fertilizer solution negated the residual lime as a magnesium source.

The chemistry of the limestone will also influence magnesium nutrition. The research presented in this article used a dolomitic lime. Other lime sources can contain less magnesium (and more calcium). It would be expected that using a limestone with a lower percentage of magnesium would further reduce the limestone as a magnesium source.

Limestone can be an important source of calcium and magnesium for a crop, but it may not be a consistent source because it is not available under all conditions. In addition to limestone, starter fertilizers are often incorporated into media in order to get consistent concentration of both macronutrients and micronutrients at time of planting. In next month’s article, we will discuss sources for starter fertilizers and their persistence in the media over time.

Leave a Reply

4 comments on “Understanding Plant Nutrition: Limestone, Calcium And Magnesium

  1. Would a limestone covering in a flower bed be a suitable covering for a decorative attraction without harming the plants depending on the ph requirement of the plants?? I am planning on a decorative bed in the yard, but do not want to harm the existing plants!! THANKS IF U CAN REPLY.

  2. Thank You So Very Much . I've been told so many different things about Cal/ Mag that I'm Washed out (Mentally) . You have saved My Day .What a simple Solution to my Problem. Please if Ya'll Have a Weekly ,Monthly Notice on Gardening PLEASE ADD MY E_MAIL ADDRESS TO IT. [email protected] Max Jackson Jr Cigar smoker & Gardener GOD Bless Our TROOPS

Latest Stories
Greenhouse Whitefly

June 26, 2016

Michigan State University Offers Tips On Whitefly Manag…

Whiteflies are making headlines in Florida, but they are found across the U.S. Michigan State experts say it’s important to know how to manage each type of whitefly.

Read More
Schaefer Exhaust Fan

June 26, 2016

What’s New In Greenhouse Cooling

Cooling and ventilation companies, as well as structures suppliers, are working to help growers manage efficiencies. Here are some of their latest innovations.

Read More
Dr Allan Armitage

June 25, 2016

Three Types Of Plant Consumers To Watch

There are three emerging groups of plant consumers that you should be targeting for plant sales in the future, according to Allan Armitage.

Read More
North Creek Nurseries lower trials

June 24, 2016

North Creek Nurseries Is A Finalist For 2016 Operation …

North Creek Nurseries in Landenberg, PA, is one of three finalists for Greenhouse Grower’s 2016 Operation Of The Year award and winner of the Excellence In Sustainable Production award for 2016.

Read More
Cal Poly Logo

June 24, 2016

Cal Poly Ag College Hosting Alumni Reception At Cultiva…

Alumni and friends of The Cal Poly College of Agriculture, Food and Environmental Sciences are invited to a reception that will be held Sunday, July 10.

Read More
Stocking spring plants at Petitti Garden Center FEATURE

June 23, 2016

How Growers Can Help Retailers Sell More In Spring

Fresh from a busy spring season, retailers share their wish list of things growers can do to make spring generate even more sales.

Read More
Houwelings Tomatoes

June 23, 2016

Houweling’s Tomatoes Has A New Corporate Head Grower

Arie van der Giessen, who has led the horticultural operations for many successful regional and national greenhouse operators in North America, will start his new role in September.

Read More
Vic Frey, Kurt Weiss Greenhouses Feature

June 23, 2016

Vic Frey Named A Finalist For 2016 Head Grower Of The Y…

Vic Frey, a finalist for the 2016 Head Grower of the Year and recipient of the 2016 Excellence In Production award, was always willing to trial and experiment with the latest technology. He loved the constant change in this industry, and turned every opportunity into a teaching moment.

Read More

June 21, 2016

Sign Up For The First-Ever Flower Run At Cultivate’16

When you pack your bags for Cultivate’16 in Columbus, OH, July 9-12, don’t forget your running shoes! There are still three weeks left to train for the first annual Luxflora Flower Run, which will kick off the start of Cultivate’16 on Sunday morning, July 10. The Flower Run celebrates Luxflora‘s mission to develop a visionary, influential floriculture network in which women leaders can create, inspire, and flourish. The 5k event is an opportunity for all floriculture professionals to come together to network, build relationships, and to have some healthy fun. Running is not required – this event is walker-friendly, as well. If you opt to be an observer rather than run/walk, then join your friends at the finish line to help shower the participants with flowers. Register yourself or your company’s team today, to join in on the fun. Free Flower Run tshirts will be available to participants, while supplies […]

Read More
BASF Orkestra Intrinsic

June 21, 2016

New Mode Of Action From BASF Offers Deeper Disease Cont…

When it comes to disease control, you need all the help you can get. BASF recently hosted growers, Extension personnel, and trade media to present its newest fungicide with two active ingredients, offering dual modes of action.

Read More

June 20, 2016

7 Garden Retailers Announced Closings This Month

Several established garden stores announced they were closing at the end of the 2016 season. Most of these retailers are decades old, including one that is closing after 133 years in business.

Read More

June 20, 2016

Industry’s First Plant Pricing Survey Is Open

The green industry has almost no research on plant pricing. With an industry that struggles to survive on slim margins, that's a problem. This survey is designed to help address the need, and we invite everyone to participate.

Read More
IGC 2016 Valley Forge Casino Resort

June 20, 2016

Stuff You’ll Want To Check Out At EIGC

Planning on attending the Easter Show For IGCs? Here's a list of new and interesting things you'll want to do while at the Philadelphia show.

Read More
FleuroStar Award Ceremony

June 20, 2016

Begonia Hybrid ‘Miss Malibu’ Takes Home FleuroStar Awar…

The award from Fleuroselect was announced at the Green Inspiration Event in Amsterdam.

Read More
Caryopteris 'Beyond Midnight Bluebeard'

June 20, 2016

Keep The Sales Coming With 16 New Blooming Varieties Fo…

Plants that put on a show from first frost long into fall and offer the color options consumers want for their gardens go a long way toward extending sales further into the season and can help maintain your sales momentum going strong. Check out these 16 new blooming varieties, both traditional favorites and new alternatives, for your fall crop selection.

Read More
Albert Grimm, Jefferys Greenhouses

June 19, 2016

Albert Grimm Named A Finalist For 2016 Head Grower Of T…

Grimm, winner of Greenhouse Grower's Excellence in Outreach and Leadership award, is always willing to listen, continuously learn, and improve. He is a role model and empowers his employees to strive for excellence.

Read More
'Osaka' Flowering Cabbage (Sakata Ornamentals)

June 18, 2016

Mark Your Calendar For Sakata Seed Trials In August

Sakata has set two dates for its California-based trials: Aug. 15-17 in Salinas, and Aug. 17-19 in Woodland.

Read More
Practical Software Grower Vertical

June 18, 2016

Practical Software Solutions Increases Accessibility, E…

Practical Software will demonstrate Grower Vertical, its customizable and scalable enterprise management system for the horticulture industry, at Cultivate’16 in July.

Read More
[gravityform id="35" title="false" description="false"]