17-06-2026 Top dressing in potatoes: this is the time to stay alert

In recent weeks, potatoes have grown rapidly due to sufficient moisture and high soil temperatures. This not only leads to fast crop development, but also to an accelerated release of nutrients from fertilisers in the soil.

At the same time, it becomes more difficult to assess exactly what is available. Especially in this phase, when demand is increasing rapidly, it is important to critically evaluate top dressing: is it necessary, when should it be applied, and in what quantity?

Because mineralisation responds strongly to temperature and moisture, conditions in the field can change quickly. Timing is therefore crucial.

Practical experience with soil and leaf analyses shows that combining these measurements helps to better understand the current situation and to make more targeted adjustments.

Why this is becoming increasingly important

Fine-tuning fertilisation is becoming ever more important. Mineral fertilisers have become more expensive, more organic manure is being used, and regulations are becoming stricter.

At the same time, mineralisation remains difficult to predict, as soil life responds quickly to weather conditions. A single warm or wet week can already make a significant difference. This requires flexible management instead of working with a fixed schedule.

What do we see in practice?

Practical experience highlights several key points to consider:

• Split fertiliser applications
  Splitting fertiliser applications often results in better utilisation than a single application. It better matches the crop’s needs and reduces the risk of leaching.

• Weather conditions and crop development
  Warm and moist weather often leads to an additional release of nitrogen. Drought, on the other hand, limits uptake.

• Field history
  After ploughing up grassland, a significant amount of nitrogen is often released, but usually later in the season. Especially when grassland is ploughed just before planting, this nitrogen may become available too late for optimal uptake. Take this into account when deciding on timing and quantity.

• Moisture availability
  Without moisture, the plant cannot take up nutrients. Under dry conditions, additional fertilisation has little effect. In practice, moisture availability is often more decisive than the amount of fertiliser applied.

Look beyond nitrogen

The focus is often on nitrogen, but other elements are just as important. Potassium, for example, plays a major role in the plant’s water management and is essential for yield, particularly in dry years. It also improves quality (less susceptibility to bruising and better frying colour).

Last year, potassium availability was insufficient. This led to more bruising and damage, particularly in vigorous-growing varieties such as Innovator, Lugano, Travolta, Agria and Donata.

Please note: a potassium application can restrict nitrogen uptake. Therefore, first determine through a soil analysis whether sufficient nitrogen is available. Based on this, you can choose either potassium alone or a combination with nitrogen. If nitrogen is also required, a compound fertiliser is preferred.

Choose the right timing

Nitrogen uptake peaks around five weeks after emergence (approximately 40 kg N per week) and then declines. Top dressing must therefore be carried out in time.

Practical guideline:

• Do not apply any more nitrogen approximately 8 weeks after emergence

Applying fertiliser too late can lead to: lower underwater weight, poorer frying colour, slower ripening, reduced storability and increased nitrogen leaching.

Final remarks

At this stage of the season, it is important to actively continue monitoring your field and not rely solely on the original fertilisation plan.

By regularly assessing the condition of the soil and the crop, possibly using soil and leaf analyses, and combining this with weather developments and moisture conditions, you maintain a clear view of the current nutrient availability.

Based on this, fertilisation can be adjusted where necessary in terms of timing, quantity and composition, so that it matches the crop’s needs as closely as possible while limiting losses.