Calcium Deficiency in California Organic Agriculture - By: Gerald Igans

Calcium is one of the most important plant nutrients. It is essential for building a strong cell membrane structure, and plays important roles in Nitrogen metabolism, protein formation and Potassium uptake. Calcium deficiencies are typically noted in the growth zones such as new top and root growth, and at the bottom end of fruits. Blossom End Rot (BER) in peppers and tomatoes is an excellent example of how weakened cell membranes reduce fruit quality and economic performance.

While the information is there, it is surprising how uninformed we are about Calcium nutrition. Although we have a practical understanding of its role as a soil amendment, eliminating Calcium deficiency in California agriculture can be challenging. Supplying the crop's need for Calcium is not as simple as calculating the soil's lime requirements. Nutrient availability is dependent upon many factors beyond total supply such as pH, C.E.C., cation saturation on the CEC, water availability and quality to name a few.

There are two factors that may influence Calcium.

1. Ca/Mg ratio: Calcium availability may be limited by excess Magnesium. Calcium is located directly under Magnesium in the periodic table of elements describing "similar" electro-chemical characteristics, which play a part in the cation exchange dynamics occurring at the interchange sites in the root zone. I personally believe that there is no magical number for Ca/Mg ratio, but that the grower should pay attention to the crop's performance and consider the total amount of Mg as a possible source of interference with Ca uptake. In this approach the laboratory-calculated fertilizer recommendations assume an advisory role, secondary the grower's experience in reading his crop's response.

2. Calcium is generally immobile once inside the plant. It moves up from the roots through the Xylem in the column of transpiration water moving up to the leaves, while very little moves down through the phloem. Because of this almost unidirectional flow, a steady supply of available Calcium is required to support cell integrity in new plant growth areas, such as shoots, roots and fruits.

Calcium Carbonate is an excellent choice material for supplying Calcium for its relative low cost, chemical purity and the low energy required to disassociate it from its carbonate counterpart. The redox reaction occurs in the presence of the weak carboxylic acids exuded by the roots and micro organisms present in the soils. Reducing the particle size increases the surface area available to be oxidized, increasing the Calcium available for plant use.

Contrary to the lab-analysis calculated approach to nutrition, a small amount of micronized Calcium Carbonate can be much more effective in eliminating - Calcium deficiency by balancing counter salts than large amounts of coarse grade liming material. The smaller particles can reach the roots by moving with the water mass flow through soil pores, creating a buffer zone around the roots that effectively balances out risk elements, such as Sodium, Aluminum and excess Magnesium. This explains why it economically makes sense to use a smaller amount of a high grade Calcium fertilizer than applying large volumes of lime that cannot reach the root zone until it is eroded by the environment.

About the Author

My name is Gerald Igans, I am an Agri-Business Developer for farms in sustainable and/or organic agriculture. It is my experience based opinion that including micronized organic Calcium in the nutrition program of specialty crops and vegetables, especially those grown in Calcium deficient soils, is important part in producing results

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