What is Calcium?

Calcium is an essential plant nutrient who’s role is vital to both plant and soil health. Its presence in the soil affects everything from soil pH and soil salinity to a soils structure. Its uptake by plants is vital to cellular health where it serves to strengthen and thicken cell walls and to regulate cell permeability. Its role as secondary messenger additionally serves to regulate various cell and plant functions from nutrient uptake to helping plants react to environmental stresses and diseases (A & L Canada Laboratories, 2005).

Natural sources of calcium include weathered soil minerals such as calcite, dolomite, feldspar and gypsum.  Applied sources include limestone, gypsum and calcium sulphate (the latter two will not raise soil pH).

Calcium’s Role in Plant Health

One of the primary roles of calcium in plant health is the key role it plays in cell walls. Calcium increases cell wall strength and thickness (Easterwood G.W., (2002)). It also serves to regulate cell permeability and is required for cell division and growth (University of Guelph, n.d.).  Other important roles and health benefits of calcium include:

• Disease reduction (Easterwood G.W., (2002)).
• Root development: short roots are often observed on calcium deficient plants (Schwartzkopf C., 1972).
• Reduces the effects of heat stress by improving stomatal function (A & L Canada Laboratories, 2005).
• Increases the efficiency of surface applied urea fertilizer by reducing ammonia volatilization (loss of nitrogen to the atmosphere as a gas) (Easterwood G.W. (2002)).
• Assists with nutrient uptake (A & L Canada Laboratories, (2005)).
• Important for nitrogen metabolism (Kelling K.A. and Schulte E.E., (2004)).
• Increases salt tolerance in many plant species (Bio-Gro, n.d.).

Saline and Sodic Soil Management

In sodic soils (which have a high pH and a good deal of sodium attached to their soil colloids) the addition of calcium (in the form of gypsum) along with some form of soil acidifier (such as sulfuric acid) will serve to displace sodium ions into the soil solution where they can then be leached away out of the root zone (providing there is no obstruction to drainage like hard pan or a high water table) (Bio-Gro, n.d.).

In saline soils (soils that have an accumulation of soluble salts to the point where they reduce the plant’s ability to take up water) drainage and flushing of the soil with clean water is the key to lowering salt levels. However calcium is also highly beneficial as it serves to increase the salt tolerance of many plant species and supports the capacity of roots to restrict sodium uptake (Bio-Gro, n.d.).

Improves Soil Structure

Calcium is a dication, (holds two positive charges), which are strongly held to the negative surfaces of soil colloids. With a positive charge on each side calcium serves to improve a soils structure by building bridges between clay colloids. These bridges help to hold soil particles together in aggregated structures which improves aeration and drainage.  Although organic matter helps to form more stable aggregates the role of calcium in low organic matter soils is vital to improving a soils structure.

Raises Soil pH

Calcium rich soils tend to have a higher pH. This is due to calcium displacing hydrogen ions from soil and organic matter colloids. These displaced hydrogen ions (H+) move into the soil solution and combine with hydroxyl ions (OH-) to form water (H20). As a result, the hydrogen ions are neutralized and unable to lower the soil pH (Young D., (n.d.)). Calcium depleted soils on the other hand tend to be more acidic. Soil pH is an important factor in plant health, as each nutrient has an optimal pH range for uptake. Adding calcium to acidic soils helps to unlock nutrients that otherwise would not be available to plants. The same is conversely true adding calcium to soils with a high soil pH will serve to lock several nutrients, up making them unavailable to plants.

Signs and Symptoms of Calcium Deficiency

Calcium deficiency is rare on soils formed from limestone and calcareous parent materials. It most commonly occurs on sandy or acidic soils and soils with low cation exchange capacity (CEC).  Calcium is an immobile nutrient; meaning is unable to move well within the plant. As such the first symptoms of a calcium deficiency tend to occur at the shoot and root tips. Terminal buds die and the edges of younger leaves develop a light green edge that may roll. Newly emerging leaves may stick together at the margins, which causes tearing as the leaves expand and unfurl (Uchida R. 2000). They may then become distorted appearing cupped and crinkled. Older leaves become dull, and the leaf margins turn brown. Stems become weak and roots may develop poorly, becoming short and thick (University of Guelph (n.d.)).

Other symptoms may include abnormally dark green foliage, premature shedding of blossoms and buds (or blossom end rot in tomatoes and watermelons), weakened stems, and death of the growing points (Easterwood G.W., 2002).

Photo Credits: photo/slide created by the author.

Updated on Dec. 18, 2021

References:

1. A & L Canada Laboratories, Inc. (2005). Fact Sheet No. 121. Calcium Nutrition in Plants. Retrieved March 20, 2014, from: http://www.alcanada.com/index_htm_files/Calcium%20Nutrition%20in%20Plants.pdf
2. Bio-Gro (n.d.). Bio-Gro’s Complete Fertility System – Alkaline, Saline and Sodic Soils. Retrieved March 19, 2014 from: http://biogro.com/resources/CFSM/BG%20CFS%2011%20-%20Alkaline,%20Saline%20and%20Sodic%20Soils.pdf
3. Easterwood G.W. (2002). Fluid Journal. Calcium’s Role in Plant Nutrition. Retrieved March 19, 2014, from: http://www.fluidfertilizer.com/pastart/pdf/36p16-19.pdf
4. Kelling K.A. and Schulte E.E., (2004). University of Wisconsin-Extension. Understanding Plant Nutrients. Soil and Applied Calcium. Retrieved March 20, 2014 from: http://www.soils.wisc.edu/extension/pubs/A2523.pdf
5. Schwartzkopf C. (1972), Mid-Continent Agronomist, USGA Green Section. Potassium, Calcium, Magnesium-How They Relate to Plant Growth. Retrieved March 20, 2014: from http://gsr.lib.msu.edu/1970s/1972/721101.pdf
6. Silva J.A. and Uchida R., eds. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, ©2000. Ch. 3 Essential Nutrients for Plant Growth: Nutrient Functions and Deficiency Symptoms. Retrieved on Oct. 30, 2021, from https://www.ctahr.hawaii.edu/oc/freepubs/pdf/pnm3.pdf
7. University of Guelph (n.d.). Introduction to Soil Science and Plant Growth Resources. Appendix C. Macronutrients and Micronutrients Source, Functions and Deficiency/Toxicity Symptoms
8. Young D. (n.d.) University of Guelph. Course notes; Introduction to Soil and Plant Growth, Module 6. Soil Chemistry

Suggested Reading:

1. Alkaline, Saline & Sodic Soils by Bio-Gro http://biogro.com/resources/CFSM/BG%20CFS%2011%20-%20Alkaline,%20Saline%20and%20Sodic%20Soils.pdf
2. Calcium’s Role In Plan t Nutrition by Dr. G. W. Easterwood  published in the Fluid Journal (2002) http://www.fluidfertilizer.com/pastart/pdf/36p16-19.pdf
3. Fact Sheet No. 121. Calcium Nutrition in Plants by A & L Canada Laboratories, Inc. (2005) http://www.alcanada.com/index_htm_files/Calcium%20Nutrition%20in%20Plants.pdf
4. Soil and Applied Calcium (from the series Understanding Plant Nutrients (2004) by K.A. Kelling and E.E. Schulte of the University of Wisconsin-Extension http://www.soils.wisc.edu/extension/pubs/A2523.pdf

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