Growers will be familiar with the macronutrients, nitrogen, phosphorus, and potassium: the important NPK 'trinity' that is the basis for crop nutrition. Yet the secondary nutrients, calcium and magnesium, which are among the 18 essential nutrients needed for robust plant growth, are easily and often overlooked.
Calcium is an essential nutrient for crop yield and quality and makes an important contribution to soil structure. It is also necessary for the uptake and transfer of macronutrients in the plant. Magnesium is equally essential for photosynthesis in the plant and for its effect on soil health.
Include calcium and magnesium in crop nutrition strategies
“Growers should consider how to manage these two important nutrients when planning their crop nutrition strategy,” says Katharina Koetting, Director Innovation & Technical Marketing Agriculture for Omya. “In some cases, crops need less of these secondary nutrients than they do of the macronutrients, but calcium and magnesium are more important, in terms of quantities required, than any micronutrient such as manganese, boron, or silicon.”
How calcium influences crop health
Calcium has low mobility within the plant and therefore a continuous supply is required throughout the growing season. It is a crucial component of plant cell walls, used as cells divide to form new roots, leaves, flowers, grains, or tubers. “Strong, robust cell walls reinforce plant tissues and promote a physically strong and resilient upright plant. This is important for preventing lodging of crops such as cereals before they are harvested,” Dr Koetting explains.
Calcium brings more than structural benefits. Established research shows that crops with optimal calcium levels maintain better plant health. Calcium improves the stability of cell membranes, reducing the release of chemicals known as 'exudates' that have been shown to attract pathogens such as fungi and bacteria. These pathogens rely on powerful enzymes to dissolve the cell wall and gain access, so when cell walls are also rich in calcium, they can better resist any attack.
But that’s not all. Calcium is also involved in root elongation, inter-cellular communication, pollen tube development and fruit set. Post-harvest, crops that received sufficient calcium in the field are more likely to retain quality in storage.
…and soil structure
“Calcium has a direct effect on soil structure,” notes Dr Koetting. “Its positive molecular charge means it is attracted to the negatively charged particles of clay and organic matter. This makes calcium a key element for stabilizing soil structure and soil organic matter, in turn helping to improve soil porosity and water-holding capacity.”
Calcium is commonly applied as calcium carbonate, which brings important additional benefits, including the ability to create a more favourable environment for beneficial soil microbes by reducing soil acidity.
As Dr Koetting explains, “Acidity is an important consideration in soil health because there’s a direct correlation between pH and bacterial activity. Studies show that the valuable nitrifying bacteria which convert ammonia into nitrates are 55 times more abundant at a pH of 7 compared with a pH of 6.2.”
Magnesium: encouraging photosynthesis and soil health
It’s not only calcium that plays an important role in plant metabolism. Magnesium is a multifunctional nutrient with a range of essential functions. Most significant is its role in plant photosynthesis, Dr Koetting points out. “Magnesium is needed for chlorophyll production, and deficiency will affect plant health and productivity very quickly. Without sufficient magnesium, the plant won’t have enough chlorophyll to capture solar energy, nor will it be able to fulfil vital metabolic functions.”
Magnesium also activates plant enzymes associated with key biochemical pathways, and phosphorus transport, phosphate metabolism, cell division and plant respiration all depend on it. Like calcium, magnesium also affects soil structure. The correct ratio of calcium and magnesium in the base saturation of a soil allows for air and water circulation in the soil and facilitates improved root penetration.
Striking a balance: calcium and magnesium in your soils
Both calcium and magnesium influence soil structure, so Dr Koetting recommends growers consider them together. “It’s important to optimize levels of each mineral for the soil’s physical and chemical characteristics and for the requirements of the specific crop. Soil analysis will help growers understand the status of the soil in the field and provide guidance for adjusting the pH and the nutrients according to soil type and crop to be grown.”
Using calcium and magnesium in soil amendment
Most agronomists and crop advisers recommend calcium carbonate for calcium soil amendments because it has a dual effect: the calcium ions improve soil structure and plant health, while the carbonate ions help to balance soil pH.
“Remember,” says Dr Koetting, “a higher soil pH not only favors soil biological activity, but also influences nutrient availability and use efficiency. Overly acidic soils can also make nutrients, such as aluminum and manganese, more bioavailable to crops, potentially causing crop toxicity.”
While calcium carbonate is readily available as agricultural lime, it is often either too coarse, reducing its reactivity, or too fine, making it difficult to apply, with potential losses due to wind-drift. An alternative to aglime is dolomite, which also contains magnesium. Although often recommended as a magnesium-correcting soil remedy, it has the same limitations as calcium carbonate if it is applied as a coarse material or as fine powder.
The solution for precision adjustment of calcium and magnesium
Omya has engineered granules such as Omya Calciprill and Omya Magprill which allow the even distribution and precise application of calcium and magnesium.
Omya Calciprill is a micronized, granulated calcium carbonate, which growers can apply with standard fertilizer spreaders, using variable rate application where needed. Omya Magprill is a similar granulated product that contains micronized dolomite, providing essential calcium and magnesium nutrition. It is ideal for soils with magnesium deficiency and low pH and can be used in place of, or in combination with, Omya Calciprill when higher levels of magnesium are required.