Developing the dosing system

From a market challenge to a practical solution The Topdresser XL, one of the latest additions to the Jongenelen Machines portfolio, is a fertiliser-dosing technology brand gaining traction in the Netherlands and Belgium.

Developed in-house and shaped by practical experience in the field, the machine addresses a challenge that Jongenelen encountered repeatedly during his career. The son of a tree grower, he explains: “The idea for the Topdresser XL emerged from around ten years of experience acquired at fertiliser company DCM. During that period, a recurring question from growers was how to make greater use of organic fertilisers and other specialised fertilisers without compromising crop safety or control.”

Using organic fertilisers in growing media requires a different approach from using mineral fertilisers, such as controlled-release fertilisers (CRFs) or base fertilisers. Their effectiveness depends on several interacting factors, including the microbial activity required for nitrogen mineralisation, changes in pH and the buffering capacity of the growing medium. Under certain conditions, high ammonia concentrations can also develop, potentially affecting plant growth.

Furthermore, various factors influence nitrogen release from organic fertilisers, making the rate of mineralisation less predictable. The growing medium’s composition also plays a role.

As a result, precise fertiliser application is essential for achieving consistent growing results.

Jongenelen notes, “One of the challenges is particularly apparent with acid-loving plants, which require a lower pH than many plants that prefer more alkaline conditions. Incorporating an organic fertiliser into the growing medium can influence the pH and therefore does not always produce the desired result for acid-loving crops.”

At the same time, relatively few machines were available that allowed growers to dose granular fertilisers themselves. Jongenelen explains: “Existing systems were often designed for a single fertiliser and were not necessarily suitable for organic fertilisers, dusty products or very fine fertiliser particles, such as microgranules. This became increasingly relevant as growers wanted to combine fertilisers with different release periods. For example, a grower might want to combine a controlled-release fertiliser (CRF) with a longevity of four to five months with another product lasting eight to twelve months, while also adding an organic fertiliser or trace elements.”

Combining different fertilisers

The idea behind the Topdresser XL was straightforward: to develop a robust machine capable of applying several different fertilisers simultaneously while handling both coarse and fine granules.

In its standard configuration, the machine can dose up to four different fertilisers at the same time. A typical combination might include an eight-month CRF, a twelve-month CRF, an organic fertiliser and a trace-element product.

“The system can also be customised,” says Jongenelen. “Recently, six machines were supplied to succulent grower Ovata in Bleiswijk, with each machine configured to dose seven different fertilisers. This flexibility is important because it allows fertilisation strategies to be tailored to groups of plants with different nutrient requirements—for example, low, medium and high-demand groups—rather than applying a single fertilisation programme across an entire nursery.”

Just as importantly, growers can see and control what is being applied.

“Once fertiliser has been incorporated into a substrate, particularly fine or organic fertilisers can be difficult to identify visually,” says Jongenelen. “With topdressing, the application is much more transparent and controllable.”

Applications across the nursery

Fewer growing-media mixes, more control

Arguably, one of the biggest benefits of the Topdresser XL is its potential to reduce the number of pre-fertilised growing-media mixes a nursery needs.

“Consider two crop groups with different nutritional requirements,” says Jongenelen. “A low-demand crop might receive two grams of CRF per litre, while a high-demand crop might require five grams per litre. Instead of requiring separate pre-fertilised substrates for every crop requirement, the grower can adjust the fertilisation at the point of application.”

The principle is simple: growers retain control of their fertilisation strategy.

Not incorporating fertiliser into the substrate in advance can also reduce the risks associated with storing pre-fertilised growing media for extended periods. If a big bale of growing medium needs to be stored for longer, applying the fertiliser closer to the time of use can provide an additional level of control.

Organic fertilisers supplied in large bales often have a relatively short shelf life, which is why growers, particularly those operating abroad, turn to an applicator that automatically dispenses a set amount of fertiliser onto the growing medium surface or delivers a measured amount of fertiliser into the base of a drilled planting hole when machine potting, as seen at Ovata.

There may also be economic benefits. Growers can purchase fertilisers themselves rather than having them incorporated by the growing-media supplier. The potential savings therefore include not only the fertiliser itself but also the cost of pre-mixing.

Jongenelen stresses that the economic case will naturally differ from one nursery to another. A grower using relatively small volumes of growing media will have a different payback period from a nursery using large quantities of fertilised substrate. Depending on its configuration and options, the Topdresser XL has an indicative purchase price of approximately €6,500–€7,000, excluding VAT and transport.

Meanwhile, pre-mixing fertiliser into growing media remains a practical option and, in some situations, may continue to be the preferred approach. Its main advantage is convenience: once the fertilised growing medium arrives, the grower does not need to manage a separate fertiliser application.

Manual application is another alternative, but adding fertiliser by hand is labour-intensive and makes accurate dosing more difficult.

From potting to pruning

Most applications currently take place at the potting machine. However, the machine can also be used when plants pass through a pruning or processing line.

This creates additional opportunities for crop management. Growers can adjust nutrition during the production cycle, for example after pruning, or provide an additional nutritional boost when required. Granular fertiliser can be applied directly to individual plants that need extra nutrition.

This offers a targeted alternative to correcting nutrient levels with liquid fertilisers, some of which may be lost outside the root zone.

For tree nurseries and other growers working with plants that remain in production for extended periods, this flexibility can be particularly useful.

Managing crop nutrition

A tool for more crop-specific fertilisation The Topdresser XL is particularly relevant to growers focusing on plant health, operational efficiency and more crop-specific production strategies.

Rather than treating fertilisation as a one-size-fits-all input, growers can increasingly differentiate between crop species and product groups.

The Topdresser XL bridges the gap between standardised fertilisation and crop-specific nutrient management. It allows growers to retain the convenience and mechanisation of machine application while bringing fertilisation decisions closer to the needs of individual crops.

This distinction can have implications beyond fertiliser efficiency. Balanced plant nutrition can form part of a broader strategy to maintain plant quality and crop health while keeping production costs at an acceptable level.

Excessive fertilisation is not only costly; it can also damage plants and cause unnecessary nutrient runoff, contributing to environmental harm. Conversely, insufficient fertilisation can lead to nutrient deficiencies, reduce crop productivity and ultimately undermine the efficiency of other resources used in nursery production.

Applying fertiliser at appropriate rates helps houseplants and nursery crops perform well while enabling growers to improve profitability and minimise environmental impacts.

What changes for the grower? The biggest change is not necessarily technical. It is organisational.

When fertilisation is managed through pre-fertilised growing media, part of the responsibility for the process rests with the supplier. “With a Topdresser XL, that responsibility shifts back to the nursery. Operators must therefore monitor the machine and ensure that the correct fertilisers are being used at the appropriate application rates.”

In return, the machine gives growers greater flexibility in how they respond to differences in crop nutrient requirements by enabling them to apply several types of granular fertiliser accurately and independently.

For some nurseries, this may mean reducing the number of pre-fertilised growing-media mixes they need. For others, it may mean making greater use of organic or short-release fertilisers, applying fertiliser more precisely to specific crops, or making targeted nutritional adjustments later in production.

Ultimately, the value of the Topdresser XL lies in putting fertilisation decisions back in the grower’s hands: What does this plant need, when does it need it, and how much should it receive?

First, there is the potential saving associated with fertiliser incorporation by the growing-media supplier. Secondly, growers gain more freedom to purchase and combine fertilisers themselves. Thirdly, more precise fertilisation can reduce situations in which plants receive more or less nutrition than they actually require, only for the imbalance to be corrected later through additional fertilisation.

The latter point is harder to quantify but can matter in practice. Instead of establishing a standard fertilisation level for a complete batch of growing media and subsequently correcting individual crop requirements, growers can increasingly tailor the dose to the crop from the outset.

The investment is approximately €6,500–€7,000 excluding VAT and transport, depending on the configuration. For a nursery using significant quantities of fertilised growing media, the potential payback can therefore be assessed against its current annual expenditure on fertiliser incorporation.