Soil Calcium cheat sheet for farmers – stuff you should know

Soil calcium can be a mystery as most growers focus on nitrogen, potassium and phosphorus. If you scan literature, scientists get very involved in detail and confusing for the average non post graduate farmer. This is a simple yet quick cheat sheet on soil calcium that will quickly give you an overview of the important aspects of calcium in the soil and its relation with crops.

Soils that have very low pH or are very acid will be deficient in Ca. Usually it is podzolic soils. You can read more at SoilsPortal for more scientific information. In general, areas with low rainfall have higher Ca levels than high rainfall soils.

Leaching of calcium in soils

Soil calcium leaching is higher in humid climates and under irrigation.

Intensive cultivation increases calcium leaching.

Application of ammonium sulfate will lower soil pH thus increase leaching

Ca in soil solution

Calcium concentration in soils are generally good except in soils with pH lower than 5

In soils with pH higher than 8.3 renders Ca inaccessible to plants because it changes to CaCO₃

Calcium availability in soils is determined by the following factors (little more scientific)

• % Ca saturation
• Total amount exchangeable Ca in the soil
• Type of ground colloids
• Type and number of complimentary cations

Distribution of Ca in the soil

Ca is absorbed by plants as a cation Ca²⁺

The distribution of Ca in maize is as follows:

• Leaves: 58%
• Roots: 20%
• Stems: 18%
• Heads: 4%

Interestingly seed contains a very low concentration of Ca. That is the reason that young seedlings need readily available Ca in the soil since they cannot get it from the seed from which they germinate.

Calcium is present as calcium oksosilacate crystals and calcium pectate that is found between sell walls.

The role of Ca in plants

• Very important role in all growth points (together with Boron)
• It stimulates the mitochondria and influences cell respiration.
• It has a direct effect on ion uptake in roots
• It helps with nitrate uptake.
• Stimulates protein synthesis
• It is involved with various enzyme systems
• Involved with cell enlargement

Interesting to note that Ca is not mobile inside the plant. Once it is fixed or used in a certain area, it cannot be removed and used in another area in times of shortage.

Ca relation to other ions (elements)

Calcium has an antagonistic effect towards other cations.

Increasing Ca concentration in the plant reduces the permeability of cell walls to other cations. This reduces the concentration of those ions in the plant as a whole.

High Ca and Mg concentrations in the soil reduce potassium uptake.

Deficiency symptoms of calcium

Ca deficiency shows in the root system first. That is why it is difficult to spot. The most important part is inside the growth point of roots. So a deficiency in the growth points will affect the whole plant. When you uproot the plant the small root system is the first thing you notice. There will also be very little hair roots that are important for taking up water.

Low Ca supply causes blossom-end-rot in tomatoes. Although the climate plays a significant role, the low calcium in the fruit cause the furthest part of the fruit to break up and rot.