Although calcium removal through harvested crops is typically moderate, this essential nutrient is often underestimated in broad-acre crop production. However, calcium plays a critical role in plant structure, signaling, and stress resilience.
This article explores calcium’s importance as a secondary macronutrient, how to recognize and address deficiencies, and how to effectively supply it—particularly through calcium carbonate and calcium sulfate.
Calcium in soil is primarily bound to soil particles and becomes available to plants through exchange from the soil particle, weathering of minerals and decomposition of organic matter. Two key factors influence calcium availability:
Soil texture: Sandy soils have fewer binding sites and lower calcium retention compared to silty or clay soils. Especially in heavy clay soils calcium promotes the aggregation of soil particles improving aeration, water infiltration, and root penetration.
Soil pH: Acidic soils (pH < 6.5) reduce calcium availability
It’s important to note that soil pH alone doesn’t provide a complete picture of calcium availability. A comprehensive soil test is essential to assess both pH and exchangeable calcium levels which is the foundation for your Calcium fertilization strategy.
Calcium is vital for plant development, ensuring strong cell walls through its interaction with pectin and playing an important role in growth, water regulation, and nutrient absorption. It helps stabilize cell membranes, making plants less vulnerable to pests and diseases, and acts as a messenger within cells to support fast responses to stress. Its role in cell signaling lets plants quickly adjust to environmental changes and trigger necessary defenses.
During reproduction, calcium supports pollen tube growth and seed set, directly affecting yields and quality. Managing calcium nutrition is key to healthy crops and maximizing agricultural productivity.
Calcium requirements differ among crops. Fruits and vegetables such as tomatoes, peppers, and lettuce are especially sensitive to calcium levels, sometimes demanding up to 400 kg/ha. Root crops—including potatoes and carrots—also rely on adequate calcium for healthy root development. Field crops like corn, wheat, sunflower, and soybeans have lower sensitivity, with needs typically ranging from 30 to 120 kg/ha. Because calcium serves primarily as a structural element, much of it remains in plant by-products; unless those residues are removed from the field, the calcium will be recycled and made available to future crops through decomposition.
Unlike mobile nutrients like nitrogen, calcium is immobile in plants, meaning it is primarily taken up by the roots and cannot be redistributed from older to younger tissues. This makes a continuous external supply, mainly through the soil, essential.
Calcium deficiency affects young plant tissues because calcium is not easily moved within the plant. Common symptoms include blossom end rot in tomatoes and peppers, tip burn in crops like lettuce and cabbage, underdeveloped roots, and leaf curling or necrosis. Low calcium reduces harvest quality by increasing lodging in cereals and lowering potato storability. This deficiency may arise from low calcium levels in the soil, limited root absorption due to drought or excess water, or competition with other cations that limit calcium uptake.
Calcium is prone to leaching, especially in high-rainfall areas or sandy soils. Annual losses can reach up to 600 kg/ha, which must be replenished ideally before crop establishment to maintain soil fertility and prevent long-term deficiencies.
Soil test - With soil testing measure exchangeable Ca (cmol/kg or mg/kg) and target between 10-20 cmol/kg (1000-2000 mg/kg) in the root zone. Assess calcium saturation and aim for a 60-70% in the Cation Exchange Capacity (CEC) to be calcium.
Tissue test - Plant tissue testing by collecting young mature leaves or specific tissues (according to crop) and ensuring that levels are within the 1.0 – 3.0% Ca in dry weight basis depending on the crop.
Two common calcium fertilizers are:
Calcium Carbonate (CaCO₃) – Also known as agricultural lime, it supplies calcium and raises soil pH. Best used when soil pH is below 6.5.
Calcium Sulfate (CaSO₄) – Known as gypsum, it provides calcium without altering pH. Ideal for soils with pH above 6.5 or where sodium displacement is needed.
Application tips:
Apply fine ground CaCO₃ products for fast reaction and Calcium release. Application can be before planting or in spring. Granulated products are ideal as they can be applied fast and easily with standard fertilizer equipment in already established crops.
Apply CaSO₄ during the growing season to correct deficiencies and to meet sulfur needs.
Calcium is more than just a structural or signaling nutrient—it's a cornerstone of plant health and soil performance. By understanding crop-specific calcium needs and using the right calcium sources at the right time, growers can prevent deficiencies, enhance stress resilience, and boost productivity.
Soil testing, informed decision-making, and proactive calcium management should be integral parts of every crop nutrition strategy.
For more information, contact us.
