Golden Tip #2, Lesson #2
Sodium toxicity in soil, after entering the plant, and eventually plant toxicity cause damage in the following ways:
High levels of sodium in the soil can lead to soil dispersion and breakdown. The reason plants suffer significant damage from sodium toxicity is the strong similarity between potassium (+K) and sodium (+Na) cations. Potassium ions (+K) move through the soil by diffusion and reach the roots. Sodium moves in the same way, and because of the great similarity between the ions—such as their hydrated radius—plant roots absorb sodium abundantly when it is available. This absorption causes fundamental changes in the opening and closing of stomata. The exchange of potassium and sodium ions among stomatal guard cells is one of the main mechanisms that precisely control gas exchange in plants.
When excess sodium is present in the soil and enters the plant, the cell membrane is severely damaged, leading to a process called cellular leakage. In this condition, cell contents leak out, causing serious harm to internal cellular mechanisms.
One important concept in plant nutrition emphasized by Emami is the Fibonacci principle in plants. According to this principle, different parts of plants—such as leaves, fruits, and flowers—are arranged symmetrically. In other words, symmetry in plants is extremely important. The healthy shape of fruit, which is essential for marketability, depends heavily on this symmetry. Any factor disrupting symmetry and shape will break the Fibonacci principle in plants. One of the key factors for maintaining proper shape and symmetry is potassium presence and minimal sodium content. The higher the sodium, the more damage occurs to the Fibonacci pattern and the fruit’s appearance.
Now that you know the harmful effects of sodium, soil types can be classified as follows:
- Non-saline soil: EC < 4 dS/m, SAR < 13, pH < 8.5, natural color.
- Saline soil: EC ≥ 4 dS/m, SAR < 13, pH ≤ 8.5, light and white color.
- Saline-sodium soil: EC ≥ 4 dS/m, SAR > 13, pH ≤ 8.5, white and gray color.
- Sodium soil: EC < 4 dS/m, SAR ≥ 13, pH > 9, dark and black color.
This classification is based on global soil science standards, which are reasonable and widely accepted by soil experts in terms of soil fertility. However, from a plant physiologist’s perspective, the situation is different.
Emami’s plant nutrition engineering principles consider this classification valid mainly for field crops. For horticulture—especially fruit orchards sensitive to salinity, greenhouses, and special green spaces—a critical limit revision is needed. Providing a fixed critical limit for a wide range of plants with varying salt tolerance is not physiologically reasonable. For example, in salt-sensitive fruit orchards such as citrus and stone fruits (apricots, peaches, cherries, etc.), decorative flower greenhouses, vegetables, and certain fruit shrubs (blueberries, raspberries), salinity has very negative and severe yield-reducing effects.
For instance, ornamental plants grown for their broad, beautiful, and green leaves suffer leaf edge burn and serious damage at EC above 2 dS/m, making them unsuitable for market. Even for salt-sensitive field crops, the global standard classification cannot be reliably used without yield reduction. For example, barley, sugar beet, and cotton tolerate EC > 4 dS/m, but wheat, chickpea, and soybean suffer yield loss at this EC. Corn, alfalfa, and sunflower may lose up to 20% yield, while beans, rice, and onion may lose more than 65% yield.
In summary, the mentioned classification was relevant in the past with older considerations and needs significant revision now.
Emami’s plant nutrition principles suggest the following classification:
Greenhouse products:
- a) EC between 1 and 1.7 dS/m: Cultivation is possible, but use fertilizers with moderate salinity index.
- b) EC ≥ 2 dS/m: Avoid cultivation until EC drops below 1.8 dS/m. If cultivation occurs, reduce long-term NPK fertilizers and increase foliar amino acid sprays.
Orchard products:
- a) EC between 0.8 and 2.5 dS/m: No major growth restrictions. Use fertilizers with moderate salinity index and avoid fertilizers containing sodium or chlorine.
- b) EC > 2.5 dS/m: Avoid long-term NPK fertilizers. Use calcium-containing compounds. Monitor conditions until EC decreases, and supply important nutrients during growth stages via foliar sprays combined with amino acids. Use hormone-containing fertilizers and seaweed extracts during critical growth stages.
Important salt-sensitive field crops:
EC between 1.8 and 3 dS/m: No major growth limitations, but since crops already grow under restricted conditions, act promptly to reduce soil EC. If suitable water and EC-lowering measures are unavailable, first identify the salt-causing element through testing. If sodium and its salts are the cause, apply calcium-based compounds such as calcium nitrate at 20–30 kg/ha or Emami-Corp disalt fertilizer at 40 liters/ha. After re-measuring soil EC and identifying dominant ions, more precise recommendations can be made.
[1] Plant Growth Regulator
