Calcium is an important nutrient which improves the quality aspects of most produce. It acts as a balance for the nutrients nitrogen, phosphorus and potassium which provide the basis of a crop’s yield.

Calcium is present in cell walls. When the supply is adequate the cell walls are stronger and maintain their integrity longer during storage.

For disease infection to proliferate they require a source of nutrients. Low calcium levels in the plant cells mean the cells become ‘leaky’. The contents of the cells leak into the areas between the cells where the diseases (fungus or bacteria) can get easy access and so develop rapidly. High calcium levels in the cell wall mean stronger cells that can resist the invasion pressure of diseases.

When new cells are formed it is critical to have an adequate supply of calcium. In the absence of calcium, root growth and tip growth will stop. If low levels of calcium are available during root and shoot development then the disorders will become visible later as a result of the plant cells collapsing.

Another role of calcium in the plant involves carrying the messages that signal a plant response to environmental factors. For instance heat, wind and frost will have greater effects on the plant when calcium levels are low, even if potassium levels are high.

Calcium moves passively into the plant and moves with the flow of water. Hence most of the calcium entering the plant will end up in the mature leaves as this is where the majority of the water is transpired from the plant. This means that plant organs that have little transpiration (fruits, tubers, young inner leaves) are especially prone to calcium related disorders, particularly when the plant’s growth rate is high.

Another feature of calcium is that it is immobile in the plant. When it accumulates in the older leaves, it stays there. It will not move out to the new leaves, or developing fruits, tubers or roots.

To move calcium into these plant parts a combination of calcium applications through the roots and as sprays onto the developing fruit or young leaf is needed. If the leaves are the only plant part receiving a foliar spray then the fruit or tuber will still be short of calcium, as it will not translocate.

As calcium is difficult to move into the fruit it is important to make sure there is a plentiful supply moving into the plant at fruit development. This helps maintain calcium levels in the fruit when it moves into its rapid development mode and becomes mature fruit.

By changing the pH due to the addition of lime, the availability, and hence uptake by plants of various nutrients, is altered. Plant growth can be improved by adding lime. This will increase the pH of acid soils, overcome a deficiency of calcium or reduce high or toxic values of aluminium, manganese, zinc or copper. A calcium deficiency is reasonably common in vegetables and fruit crops.

In annual crops, and when preparing to sow a new pasture, lime should be applied several months before planting and be incorporated into the soil, to give it time to react.

Where crops are grown in rotation with pasture, lime is best applied during the cropping, rather than the pasture stage. This allows an opportunity for the lime to be mixed into the soil by cultivation.

In permanent pasture, it is necessary to apply lime to the soil surface. Incorporation may not be possible, due to topography (eg. steep terrain prone to erosion) or other reasons. When incorporation is not possible, it will take longer for the lime to move into the soil. Responses may be slow to occur, and may not become evident for several years.

When soil calcium levels are low then calcium applications will be needed to ensure healthy plant growth and production. If the soil is acid then calcium may be made unavailable to the plant. When the soil is alkaline then calcium levels are often adequate for most plant growth.

Calcium is usually added to soils as lime (calcium carbonate), dolomite (calcium and magnesium carbonates), gypsum (calcium sulphate) and superphosphate. The effects of each differ considerably.

If lime or dolomite is added, the soil pH is raised, the extent of the rise being dependent on the soil’s ability to return to its original pH after alteration and the quantity, purity and fineness of the lime added, along with its neutralising value.

When gypsum is added to a soil, the calcium sulphate dissolves in the soil solution. The clays then become calcium clays with a much improved structure compared to the sodium-dominated clays.

Calcium compounds (lime, dolomite and gypsum) are less soluble than the fertilizers containing nitrogen, phosphorus and potassium. For calcium to become available to plants, it must be applied early enough for the calcium to enter the soil solution and/or to become attached to the cation exchange sites on the clays.

Lime and dolomite are generally ground to improve their effectiveness. The finer the particle size, the more readily available is the calcium.

Where the soil pH is less than 6.0 and both calcium and magnesium levels are low, dolomite or lime plus magnesium oxide should be used.

Where the pH is less than 6.0 and the calcium level is low then it is best to use lime.

Where the pH is 6.0 or higher and either calcium is low and/or sodium is high then gypsum is recommended for use.

Calcium is an important nutrient for plant development and production of quality fruit, vegetables and tubers. However calcium is not the only nutrient required. A balance between all the plant nutrients is essential.

The nutrients with the most influence on the availability of calcium are potassium, magnesium and ammonium. If one or more of these nutrients are dominant then the availability of calcium, even though it may be in adequate supply, will be diminished.

The key is to maintain a balanced nutritional program for all the nutrients required for your crops production.

The Wamuran Co-op can supply the following products that support a calcium requirement: Natural gypsum; Ag lime; Dolomite; Grow-mag; Calcium nitrate (water soluble) and Liquid Stopit. Why not call in and discuss your needs with our friendly staff.