Common misconceptions in durian care

Having identified the pathways through which cadmium can enter a farming system, the next question that troubles growers most is: why do orchards under similar growing conditions show different levels of risk, with some remaining stable while others do not?

According to experts, the answer does not lie in any single factor. Input materials, soil characteristics, cultivation history, and long-term nutrient management practices can all affect a tree's capacity to absorb cadmium.

Notably, some long-standing care practices once regarded as "proven experience" are now being reconsidered. Applying more fertilizer does not necessarily make a tree healthier, and a product labeled organic does not necessarily restore soil.

Misconceptions about humic acid and liquid organic products

In recent years, alongside a trend toward reducing dependence on chemical fertilizers, many growers have begun switching to products marketed as organic. But according to experts, a fairly common confusion exists between genuine organic fertilizer and liquid organic products.

Tran Thanh Tam, Director of the Dong Thap Province Sub-Department of Plant Production and Protection, said many growers now use humic acid, a dark-colored organic solution, or liquid organic products, viewing them as a complete substitute for traditional organic fertilizer.

He said this understanding is incomplete. Liquid organic products can support a tree's physiological activity or improve nutrient exchange during certain stages, but that does not mean they restore soil structure.

Meanwhile, what long-cultivated soil actually needs is a sufficiently large addition of organic matter to restore its "health", a fibrous organic source capable of retaining moisture, improving soil friability, boosting pH buffering capacity, and creating an environment for beneficial microbial communities to develop.

Professor Tran Van Hau, PhD (former senior lecturer at Can Tho University), also noted that relying solely on humic acid or liquid organic irrigation is unlikely to deliver the physical soil improvement growers expect. Soil does not recover simply by switching fertilizer types. Soil recovers when its structure is rebuilt.

A separate survey pointed to a related issue: the problem lies not only in which inputs are used, but in how they are used.

According to Dr. Tran Thi My Hanh, Head of the Plant Protection Department at the Southern Horticultural Research Institute, a survey of roughly 90 durian orchards found a fairly common pattern. Nitrogen levels were typically adequate or high. Phosphorus was, in many cases, applied well beyond actual crop needs. Meanwhile, potassium and secondary and micronutrients were not being supplemented proportionately.

According to Dr. Hanh's research team, prolonged nutrient imbalance does not necessarily equate to cadmium residue in fruit, but it can affect a tree's uptake patterns. This is exposing the limits of the "apply whatever is lacking, raise the dose if weak" approach. Under intensive cultivation conditions, trees need not just sufficient nutrients but a balanced nutrient state.

Notably, calcium, magnesium, and zinc are considered to play an important role in maintaining nutrient balance, and according to expert analysis, they may help reduce the risk of cadmium uptake through competitive mechanisms at the root zone.

However, experts also caution that actual effectiveness depends on soil conditions, water regime, and the overall cultivation process. There is no single formula that applies to every orchard.

The important role of soil pH

One of the most frequently cited factors is soil pH. In the past, growers focused on pH mainly for its effect on plant growth or fertilizer uptake.

But in the context of cadmium, pH carries additional significance. According to expert analysis, as soil becomes more acidic, cadmium tends to shift into a more soluble state, increasing the likelihood of root uptake. This puts orchards that have been cultivated for a long time, rely heavily on chemical fertilizer, or receive little organic supplementation at higher risk of elevated cadmium residue in their produce.

Tran Thanh Tam said this is why many current soil restoration models need to focus on three groups of solutions: adding a sufficiently large volume of organic matter, controlling soil pH, and improving soil physical properties. He said that raising pH with lime alone, without improving soil structure, is unlikely to sustain results over the long term. What growers need is not a favorable reading in the short term, but a stable soil condition sustained over many years.

Nguyen Van Hanh, a durian grower in Ngu Hiep commune, Dong Thap province, raised a very practical concern. He said the gap between technical recommendations and actual production conditions remains fairly wide. Maintaining soil pH at a target level over the long term is not simple for orchards that have been under cultivation for many years. Soil improvement costs are high, conditions vary from orchard to orchard, and not every household has the means to experiment. Growers, he said, would welcome more specific procedures tailored to different soil groups rather than general guidelines.

Professor Tran Van Hau said soil restoration is a long-term process. Growers should not expect soil to reach an optimal state after just one treatment cycle. The appropriate approach is to gradually reduce risk factors at the input stage, improve the soil environment, and adjust nutrient regimes toward greater stability. For the durian industry, pressure from cadmium concerns is forcing growing areas to revisit an old but still highly relevant issue: soil is not merely where roots sit, but the foundation that determines fruit quality and the competitiveness of an entire growing region.