All over the world a similar NPK indication is used on fertiliser packages. In the Netherlands, it is still possible to write these as weight in volume.

Most countries abandoned this way of measuring years ago.


What exactly is measured?

In the laboratory, the fertiliser is diluted and then the values ​​of the (trace) - elements are measured. These values ​​are converted into a table for the percentages in the fertiliser.

On the package we note the elements in percents but also the percentage of that part of the element, which is completely soluble in water.

Clearly marked on the front of a package is the N-P-K value, expressed in percentages of the total element.


What is the N-P-K value?

The NPK value represents the ratio of nitrogen (N), phosphorus (P) and potassium (K).

Nitrogen is necessary for the growth phase of the plant. This ensures that the plant grows to a large size, and bears large green leaves and large fruits/flowers. Nitrogen should be added carefully to the plant, so it does not get too much or too little.

An excess of nitrogen causes an excessive growth of the plant. In flowering plants you notice that there is an excess if it does not flower or flowers late.

A shortage of nitrogen yields a poor growth with small leafs and a yellow-green colour. The yellow-green colour is caused by a lack of chlorophyll.

Phosphorus is necessary for the formation of protein in the plant. Protein ensure that the stem and the fruits develop firmness and the seeds become fertile. It also affects the production of vitamin in the fruits. Phosphor also has a positive impact on root formation.

An excess of phosphorus inhibits the uptake of metals such as iron, copper and zinc, resulting in growth defects and leaves turning yellow (chlorosis)

A shortage of phosphorus can be seen in the growth and flowering of the plant. This will occur later and it will take longer before the plant will start to develop fruits/flowers. The plant will also be less hardy. A phosphorus deficiency is identified by a red-brown discoloration of the leaves.


Potassium is required for the firmness of the plant. For the development of starch and sugar in the plant a plant needs plenty of potassium. Also, the flowering and fruit setting and the sustainability of the fruit is influenced positively. A crop that produces much starch and sugar will therefore need more potassium.

An excess of potassium causes more water in the plant, but also inhibits the absorption of magnesium and boron in the plant.


A shortage of potassium causes diseases such as fungal diseases. The edges of the leaves are brown and will die off, just like the plant.

The difference between W/V and W/W

The designation W/V stands for Weight/Volume. Weight/Volume is a measuring method.

The fertiliser is dissolved in water in volume. For example: take 1 litre of osmosis water and dissolve 1 ml of fertiliser. 1 litre of osmosis water equals 1 kg (this is a given fact). This water now represents the weight (Weight (W)).

1 ml fertiliser represents the volume (V)


The designation W/W stands for Weight/Weight. Weight/Weight is the measurement method that is used worldwide and which we will use also.

Here, the fertiliser is dissolved in water in weight. For example: take 1 litre of osmosis water, which we already know is weighing 1 kg and dissolve 1 mg of fertiliser in it. Both the osmosis water and the fertiliser are now added in terms of weight. This gives the measurement in W/W.


What value will now change?

The familiar NPK value on the package will show a lower value in the immediate future.  Instead of W/V behind the NPK value, you will now see W/W behind the NPK value.

The values ​​will look lower, but the recipe and the dosage remain the same. Your trusted product will work the same as you have been getting used to over the years.

Actually nothing will change, except for the packaging.


Why are the values ​​lower?

The current values ​​are lower because the specific gravities of fertilisers have their own weight. All liquids have a different weight and only in the case of osmosis water 1 litre is actually 1 kg. !:!

We have read before that the specific gravity of Osmosis water is 1 kg. Thus, each fluid has its own weight. So one cannot say, as in the case of osmosis water, that 1 litre of fluid indeed weighs 1 kg. It often happens that a liquid is heavier than water, but it may also be lighter than water. * For example: 1 litre of fertiliser may weigh 1.12. And from a different fertiliser 1 litre weighs 0.98 kg.

You see here that when you take 1 ml of a product it is not directly 1 mg as such. It may for example* be 1.12 mg or 0.98 mg. This means that the conversion of W/V will look differently if we dissolve 1 mg of fertiliser in 1 litre of osmosis water, instead of 1 ml.

Example: 1 ml of fertiliser, having a specific gravity of 1.18 mg, will yield different values when dissolved in 1 kg of osmosis water than ​​when 1 mg is dissolved in 1 kg of osmosis water. With 1 ml (= 1.18 mg) you dissolve more than 1 mg and therefore the values are ​​higher.


* Example:

1 ml (1.18 mg) liquid fertiliser in 1 kg of osmosis water = W/V

1 mg (0.82 ml) of liquid fertiliser in 1 kg of osmosis water = W/W


If you have any questions after reading this explanation, please contact us or 0031 (0) 73 522 32 56


* = An example, the above values ​​are fictitious because every liquid has its own specific gravity.

- Daily.

- Weekly.

- Add 1x per 2 weeks to the irrigation water or use it during theflowering stage of the plant.