The Role of Calcium (Ca++) in Plants

Part 1 – What is Calcium?

Calcium as it is defined on the Periodic Table of Elements is an alkali metal atomic number 20 with a relative atomic mass of 40.078.  Calcium in its ionic form is missing two electrons on its outer ring for stability making it a cation.  In order to make Calcium stable it must be bound to negatively charged ions (anions) such as a nitrate or a phosphate.  This positive charge makes this element also interact greatly with substrate.  Clay particles are the particular part of most substrates that make cation exchange possible.  Most clay structure exhibits an overall negative charge across its surface.  This makes Calcium particularly attracted to it.  Exchange Capacity is defined by Maarten J. Chrispeels and David E. Sadava as “The total amount of available plant nutrients bound to soil particles is called the soil's exchange capacity, a parameter that determines soil fertility.” Therefore a more important measurement to a plant is a soil’s Cation Exchange Capacity (C.E.C.).  C.E.C. is defined as the potential for total positive charged ion exchange between the root and the substrate.  In a plant, Calcium plays a major role even though it is considered a secondary nutrient.  Macro nutrients Nitrogen (N), Phosphorus (P), and Potassium (K) are all geared on the plants ability to reach Calcium stores in the mineral solution or soil solution.  Calcium plays a major role in plant cell stability, uptake of water, as well as the protein pump that regulates nutrient uptake (Patterson, Greg; Calcium Nutrition in plants).  In our industry we have to understand very different concepts of plant nutrition and availability than one might in agriculture in natural soils.  Calcium is a source of disease prevention and treatment, heat stress prevention, increased transpiration rates and crop yields.  Calcium and Magnesium are also known for their pH buffering abilities.

In hydroponics in a synthetic mineral solution, Calcium has its greatest availability to the plant at pH 5.5 to 6.4 and limited availability above 6.8.  However in a soil medium, especially in the presence of natural microbes, Calcium has a much broader range of availability depending upon the plant (5.5-7) but is affected greatly by other factors such as soil alkalinity, the presence of anions in the aqueous soil solution, and the total C.E.C. of the medium being used.  Common media in hydroponics are hydroton (high C.E.C), perlite (low C.E.C.), Rockwool (low C.E.C.), Rocks (high C.E.C.), coconut coir (medium to high C.E.C), gravel (medium to high C.E.C), etc.  Each of which can be mastered knowing the media, its C.E.C. and interaction with Calcium in particular, and by knowing more about the mineral or organic solution being used.  Calcium uptake in a plant happens at the plants fine root hairs root tip. Therefore a media needs to have a good bulk density (porous or fluffy) in order for the roots to penetrate, but still have enough clay particle or other particle that has a higher C.E.C. in direct contact with the root so that Calcium is available in lower saturation.  Certain amino acid stimulates like L-Glutamine and L-Glycine help generate more zones in the root structure for greater cation uptake.  Surprisingly small amounts of sodium are used in this process.

In part 2 we'll cover Calcium uptake and deficiencies.