Changes in soil pH and the method of using organic fertilizers are two factors that can affect the level of dissolution and accumulation of Cadmium in crops. Notably, during fruit-bearing seasons – especially when water levels are low and soil pH decreases – the ability of Cadmium to dissolve increases, leading to the risk of heavy metal residues in agricultural products. In addition, the uncontrolled use of organic fertilizers also has the potential to increase the content of heavy metals in soil and crops.
1. Impact of soil pH on Cadmium Solubility and Accumulation
Cadmium is a toxic heavy metal, often existing in the soil as insoluble or slightly soluble compounds. However, the solubility of Cadmium depends largely on the pH of the soil. When soil pH decreases (soil becomes acidic), especially in the dry season or when water recedes, the ability of Cadmium to convert from an insoluble form to a soluble ion form (Cd²⁺) will increase. This ion form is easily absorbed by plant roots and accumulates in plant parts, thereby leading to residues in fruits and agricultural products.
Many studies show that:
Under low pH conditions (acidic soil): Cadmium ions (Cd²⁺) become more soluble and are easily absorbed by plants through the roots. This is the reason why low-lying areas, acid sulfate soils or arable land that is frequently flooded – after the water recedes at the right time of fruiting – are very likely to record higher than permitted levels of residual Cadmium.
In high pH conditions (alkaline soils): Cadmium tends to be retained as a precipitate or adsorbed by clay particles and organic matter, reducing mobility.
2. Risks from uncontrolled use of organic fertilizers
Organic fertilizers are an essential source of nutrients that help improve soil, provide sustainable nutrition and improve the physical, chemical and biological properties of the soil. However, the composition of organic fertilizers is very diverse, depending on the source of raw materials used.
In some cases, industrial or homemade organic fertilizers can use raw materials such as:
✅ Industrial sludge, pond sludge
✅ Waste from processing plants
✅ Unknown mixed additives root
If not strictly checked, these materials may contain high levels of heavy metals, especially Cadmium. When used in the correct dosage and with standard fertilizer sources, the heavy metal content in the soil will not be significantly affected. However, if farmers overdose, or use it continuously for a long time, heavy metals can accumulate in the soil, and over time will become a potential source of residue.
If gardeners have a habit of using it excessively or continuously for many crops, especially in acidic or low-lying areas, Cadmium will gradually accumulate in the soil. When the soil pH decreases in the dry season, this Cadmium will easily dissolve, increasing the risk of heavy metal residue in agricultural products.
3. Recommendations on management solutions
To limit the risk of Cadmium residues in crops and agricultural products, a number of solutions need to be implemented synchronously:
✅ Monitor and adjust soil pH periodically, especially at the time of flowering and fruiting. Maintaining soil pH at 6.0 – 6.5 will help limit the dissolution of Cadmium.
✅ Check the origin and quality of organic fertilizer before use. Prioritize organic fertilizers that have been certified by VietGAP or international organic standards.
✅ Do not overuse homemade or untreated organic fertilizers.
✅ Use Wokozim balanced trace minerals to limit the accumulation of heavy metals in the soil is a solution being applied by many gardeners.
✅ Improve the soil with plants that absorb heavy metals well such as Vetiver grass, sunflower, cockscomb, amaranth… to absorb Cadmium from the soil.
Conclusion
Changes in soil pH and uncontrolled use of organic fertilizers are two key factors affecting the level of Cadmium residue levels in agricultural products. Actively managing soil pH, controlling organic fertilizer sources and applying safe farming practices will help farmers protect long-term soil quality while ensuring food safety and public health.
This article was written by: Technical Department – Agriculture Department – Vinhthinh Biostadt Company
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