Issue 6 2018
Counting on the contribution of calcium
Calcium is much more important to plant growth than many people realize. So as one of the four essential plant nutrients in Polysulphate™, in this Missive we shine the spotlight on calcium to share with you this refresher on the nature and extent of calcium’s contribution to crop growth, health and productivity.

Multiple roles of calcium

We all know that calcium is one of the four essential plant nutrients in Polysulphate. But collate exactly what calcium does for crops and the list is impressive. To sum it up we can say that calcium is a crucial regulator of growth and development in plants. But to properly spell out calcium’s roles we have to include all of the following:
  • crucial for plant cell division and strong cell walls
  • improves nutrient absorption by roots and translocation through plants
  • activates plant growth-regulating enzymes
  • helps convert nitrate-nitrogen for protein formation
  • contributes to improved disease resistance

OK. Calcium is involved in every part of the plant and at all times during its growth. But calcium is not a great mover. It can only transfer from one part of a plant to another through the xylem sap. If the plant calcium runs out, it cannot remobilize calcium from older tissues.
When calcium is in short supply

Sadly, not every crop gets the calcium it needs. The range and seriousness of the consequences of calcium deficiency are seen by too many farmers.

Looking at the whole plant, key calcium deficiency symptoms are that new leaves are distorted in shape and the whole growing tip may die off. Meanwhile below ground the root tips die and overall root growth is very slow.

Look at the cell level and one of the most serious results of inadequate supply of calcium is the deterioration of plant cell membranes. Without robust membranes, the cell compounds leak out and the cell, and on a bigger scale the plant tissue, dies. Even small-scale damage can be devastating for crop quality and value.
Calcium for crop quality

It has long been understood that many physiological disorders are associated with poor calcium. Apples can suffer from bitter pit and internal brownspot. Cabbages get internal tipburn. Carrots get cavity spot. Celery has blackheart. Potatoes get hollowheart and poor skin. Peppers and tomatoes fall victim to blossom-end rot. All these crops store poorly when calcium is deficient.

When it comes to crop diseases, many organisms that infect plants do so by penetrating the cell tissue with enzymes known as pectinase, which dissolve pectins. The higher the calcium content in plants, the higher the concentration of pectins holding cells together and the greater the ability to withstand these enzymes. Therefore the crop becomes more resistant to diseases.

The dreadful consequences of calcium deficiency make it all the more important that its widely understand how plants get their calcium and what from.

The difference available calcium in soil makes

Calcium is as important to the soil beneath plants as it is to growth above it. In soil, calcium helps maintain chemical balance, reduces soil salinity, decreases soil crusting and improves water penetration.

Farmers often apply calcium-containing soil amendments, such as lime or gypsum, to their land. However, we should not confuse the benefits of such soil amendments containing calcium, with the need for available calcium for plant uptake. Many believe incorrectly that application of mineral amendments to soils will do two jobs in one: enhance the soil and sufficiently supply the calcium requirement of crops. That is not the case.

The truth is that calcium-containing soil amendments and calcium fertilizers have different roles. They can complement each other but cannot do each other’s work.

Polysulphate: the perfect calcium source

Yes, Polysulphate perfectly provides available calcium to crops. Here’s just a little biochemistry to explain what makes it so perfect.

Plants take up Ca as the Ca2+ cation. In Polysulphate, calcium is present as calcium sulphate (CaSO4), which dissolves in the soil solution as SO42- anion and Ca2+ cation, just as plants like it from the tropics to the temperate regions and everywhere in between.

Polysulphate is a great calcium source for tropical, acidic soils where Ca deficiency is often found. In addition, Ca supply through Polysulphate can alleviate aluminum and manganese toxicity symptoms which are common in those regions.

In sandy soils where calcium can be easily leached by rain or irrigation water, there can be a Ca shortage which Polysulphate can easily correct.

Because, as explained above, calcium does not relocate in the plant, it is very important that it is available throughout the growing season. Our solubility laboratory experiments show that Polysulphate releases calcium steadily, thus providing prolonged calcium availability through the crop cycle: perfect.

Of course, in Polysulphate calcium sits as one of four powerful and key nutrients (Ca, K, Mg and S). Perhaps we should turn the spotlight on one of the others in a future edition of the Missive?
Calcium deficiency in grapes (Jiaxing, Zhejiang Province, China)
Mined in the UK, ICL is the first – and only - producer in the world to mine polyhalite, marketed as Polysulphate