Academy – Calcium

Calcium is an essential element for plants, which influences both the quality of the crop and the structure of the soil. In this article we take a closer look at the function of calcium for plants, in what forms it occurs in substrates, and what the effect is of a calcium deficiency or excess.

Calcium in substrate
Calcium mainly occurs in substrates in the form of lime fertilizers (to increase the pH) and calcium nitrate (also called lime nitrate, to increase the nitrogen content). When using lime fertilizers, the available calcium is largely bound to the absorption complex of the substrate. The calcium from these lime fertilizers is then slowly released during the dissolution of the lime. This also applies to the addition of clay. Many calcium ions are strongly bound to the complex, and are therefore not present in large numbers in the solution.

When using lime nitrate in the substrate, in addition to Nitrate, Calcium is also added to the solution. Progressive insight through research tells us that the calcium figure in a solution increases faster by adding calcium nitrate compared to increasing lime fertilizers.

With the loss of CALMAG we have lost a good slow-acting source of calcium. In mid-2023, Lensli and the RHP examined calcium sulphate (gypsum) as a possible alternative. This has also proven to be a good source of calcium, but has the disadvantage of a lot of sulphate input and a high EC. As a result, we do not really see many possibilities yet, partly because we have lime nitrate as a more logical alternative.

Calcium in the plant
Calcium is the plant's most important building block for membranes and cell walls. The element is necessary for cell division and contributes to the strength of the plant. Transport of the calcium ions (Ca2+) occurs almost exclusively via the root tips.

The transport of calcium in the plant is related to sap flow. The evaporation of the plant therefore affects the absorption. If a plant cannot evaporate properly, for example due to excessive humidity, the calcium supply to the growing points, leaf edges or fruit tops will be reduced.

The concentration of calcium in the solution is partly determined by the amount of other cations, such as potassium and magnesium. The absorption of calcium is more difficult than some other cations, such as potassium. The element calcium is also less mobile in the plant. If fertilization with potassium, for example, is too one-sided, displacement of the absorption and transport of calcium ions can occur.

Calcium deficiency can be caused by an poor balance in the nutrient solution. In practice, it is particularly important to pay close attention to ensure that the cation balance is in order. For the K-Ca-Mg ratio, a normal balance is around 4-2-1 in the solution.

Examples of calcium deficiency or poor cation balance are:

• blossom end rot in tomatoes or peppers;
• tip burn in strawberry;
• necrosis in carnations and roses;
• brown dots in conifers.

Calcium in peat-free compositions
As explained earlier, Calcium is an essential element for crop growth and quality. Absorption deficiency can lead to weakness and necrosis. Peat-free substrates have a different cation balance than peat-containing substrates. Particularly in the tree nursery, it is smart to closely examine the analyses. In this sector we are often dependent on slow-acting coated fertilizers (which do not contain calcium) and in the future (due to less peat) a lower lime requirement. If calcium is present in very high concentrations in the solution, it can precipitate with sulfate and phosphate. Poorly soluble calcium salts such as calcium sulphate or calcium phosphate are then formed. However, in practice this rarely happens.

Consult with your Lensli account manager whether the figures in your analyzes indicate a favorable or unfavorable nutritional status.

Do you have questions or would you like to know more about this subject? Please contact your Lensli account manager or our Substrates Technical Product Manager Nick Vollmer by email n.vollmer@lensli.com or telephone +31 (6) 51269415.

We are happy to talk to you.