CALCIUM – An Essential Mineral for Soil Structure, Plant Nutrition and Produce Quality
As the title suggests, calcium is the king of nutrients because it impacts the soil, the plant and the fruit produced. We will look briefly at each of these areas, realizing that it generally requires three different forms of calcium to address each of the three end uses.
Soil structure refers to the size, shape, and arrangement of stable soil aggregates; each clump or aggregate of soil consists of individual mineral particles, pieces of organic matter and the ever-present microorganisms. Individual soil particles are stuck together by charged clays, carbonates, ionic bonds and root and microbial exudates. The arrangement of these soil aggregates determines the size and quantity of pore space, and it primarily influences plant growth by the extent of root distribution and how water infiltrates and percolates through the soil. While excellent soil structure encourages rapid plant growth and top production, poor structure hinders it.
Ensuring the presence of adequate soil calcium will provide the best soil structure. Calcium cations, with their double positive charge, improve soil structure by bridging soil organic matter with clay particles resulting in better aggregation of soil particles. We refer to this calcium as exchangeable calcium; it freely exchanges with other cations on the soil exchange sites. Common soil amendments such as gypsum and limestone are excellent calcium sources and can be applied in high enough rates to impact soil structure. When the calcium salt is dissolved, calcium ions are free to move within the soil matrix where they are either attached to the soil exchange sites, combined with other anions, or suspended in the soil water. Most of this mineral calcium works to enhance soil structure.
As a nutrient for plants, calcium is indispensable. It’s an essential element in the structure and permeability of the cell walls and membranes of the plant, and it’s essential for cell elongation and division. Calcium does not translocate easily within the plant and is generally immobile. Calcium moves into the roots in the transpiration stream – nutrient rich soil water flowing from the roots to the shoots, released as vapor through the stomata in the leaves, with the mineral nutrients left behind. Since calcium does not translocate easily, we ensure a regular supply of “soluble” calcium in the soil water. Fertigated liquid calcium products such as CAN-17 (17% nitrogen plus 8% calcium), calcium thiosulfate (6% calcium) and calcium chloride (12% calcium) are all used to meet the demand for “soluble” calcium. These calcium sources can be applied repeatedly throughout the season, ensuring that calcium is moved quickly to the plant for uptake and use in plant structure.
The quality of our produce is greatly influenced with calcium. It is the nutrient that gives lettuce its “snap” when you first bite into it, it’s the nutrient that pevents fruit disorders like blossom end rot in tomato, and it’s the nutrient that maintains fruit integrity in the long term cold storage of apples. The best way to get it there is with a foliar application. Since there are no stomata in fruit, very little soil applied calcium is translocated thru the plant vascular system and placed directly in the fruit. To correct this, we often use foliar applications of calcium to deposit calcium on the fruit surface. Foliar-applied calcium is chelated with special compounds to aid in the movement of the nutrient across the outer waxy layers of the fruit and into the inner cellular structure. Chelated sources are also best used when tank mixing with other nutrients.
Calcium is one of the most important minerals used in production agriculture. There is no single calcium source that provides calcium for soil structure, plant structure and fruit quality. We often rely on multiple applications of several different calcium products to ensure that calcium is applied at the preferred timing, in the proper rate, and at the correct place.
- Dow Wolf - Agronomist