The role of Potassium (K) in fertilizer

Potassium is one of the 3 traditional main elements in fertilizer, namely N-P-K. Nowadays we also include Ca and Mg as important elements. Potassium is a chemical element with symbol K, that is chemically similar to Sodium (Na) which is its neighbor in the periodic table. Pure Potassium is silvery-white metal that reacts very fast with oxygen to form Potassium Peroxide (K202). The name Potassium (Kalium in Latin) stems from the fact that is used to be derived from ashes that were collected in burn-pots. This “Pot Ash” was in fact already used as a fertilizer before the industrial era. Nowadays, Potassium is mostly derived from salts that are mined or extracted from ancient lake bottoms and seabed. Also, in the Dead Sea between Jordan and Israel, potash is extracted from the water. However the largest deposits are currently mined in Canada. After mining, the salts are separated and most Potassium actually ends up as Potassium Chloride also known as Potash or MOP (muriate of potash).

What is K’s role in fertilizers?

In Fertilizer, Potassium is an essential component, together with Nitrogen and Phosphorous (NPK). Approximately 95% of all Potassium production in the world is used to grow plants. The presence of K in plants usually ranges between 0,5-2% of the weight. In fact, K is so common that in every adult human body there is roughly between 100-180g present at any given time.

In plants Potassium makes plants “harder” by maintaining turgor pressure of cells, which keeps them from wilting. Furthermore, Potassium plays an important role in proper functioning of stomata which control the “breathing” of plants. Potassium is also co-responsible for vital processes such as water and nutrient transportation, as well as protein and starch synthesis. Plants that lack K will start to show yellowing (older) leaves, followed by necrosis and/or stunted growth.

In practice, K-rich fertilizer is used by growers to make the plants harder and more resistant to stress such as cold and drought. Potassium is used by crop producers to enhance fruit-size, -quality and -flavor. In turf, K is used to make turf harder and more drought resistant.

How does Mivena apply K?

Mivena works in very different market-sectors, ranging from high-end golf-courses in Spain and Portugal, to soft-fruit growers in the Ukraine and municipality sport fields in Finland. It is therefore very difficult to have a general recommendation about Potassium by us. The only thing is that in the natural cycle of any plant, it will demand more Nitrogen in the start phase, N:K = 1:1 in the middle and more K at the end. It’s up to the user to decide when these phases commence and end. Another point is that the balance of K-Ca-Mg is very important, since these elements strongly interact with each other. About the ideal ratio, we can say that Ca-Mg are roughly equal and K should be at least double the amount of Ca and Mg.

In turf, Potassium demand generally starts in (early) summer when the grass needs to be tougher to withstand heat/drought as well as grow less. Then in fall and winter, turf will also demand more K, if anything to withstand the cold. We will advise applications of Granucote, Greenstar, Granuform and Granusports depending on the situation that are balanced either N:K = 1:1 or 1:2.

For plant nurseries, the needs for the plants are less seasonal demand driven, but more geared towards plant specific needs. Some nurseries, especially ornamental, want more compact growth with shorter stronger plants. They will use our Horticote Plus formulas to mix in the substrate or Horticote Topdress to re-apply some CRF doses for an extra 6 to 8 Months.

Fruit-bearing plants growers will usually increase the Potassium dose to a N:K ratio of max 1:4 (!!) to boost flower and/or fruit production. They will more likely boost these ratios by running high K varieties of Granusol and Granufert through their irrigation systems.

Mivena products with high K:

Granucote CRF 12-5-24
Especially suited for fairways. Will be applied in September/October with durations to last until February/March of the next year.
Greenstar CRF 15-0-22
A slightly coarser granule than Granucote and only available in 3M durations. Is often used in Fairways and Roughs, but also in landscaping and garden maintenance.
Granuform SRF 16-0-22 / 19-0-19 / 19-5-17
Very small granule, extremely suitable for Tees and Greens. Will give enough nutrients for 2-3 months.
Granusports SRF 8-0-26 / 19-5-17 / 19-0-19
Similar to Granuform except a larger granule. Is more suited for sports fields and some tees. Will also give enough nutrients to turf for 2-3 months.
Horticote Plus CRF 14-10-18 + Traces
Available in 4-6-8-12 Month durations. 100% coated NPK granules, very suitable for mixing in substrates for longer grow-periods.
Horticote Topdress 14-7-20 + Traces
Partly coated fertilizers used to apply on pots where the plant is already established. Suitable for nurseries that need to give a little extra dose of fertilizers to generally larger pot-sizes
Granusol WSF 10-10-30 / 12-7-25 / 4,5-11-36
Highly soluble crystalline powder that is suitable for any form of irrigation. All formulas contain a high dose of trace-elements and Mivena’s special vitamin mixture with many benefits that improve plant vitality, health and nutrient uptake
Granufert WSF 6-8-30 / 10-5-23 / 13-6-24
Highly soluble powder that is most suitable for fertigation systems. Some products contain additional CaO for improved fruits
Which Potassium should we use on Turfgrass?
We at Mivena are a bit surprised when customers ask for (uncoated) Potassium-Nitrate in their fertilizers for autumn or winter. Especially in tenders for municipalities, we often come across these demands. Besides the fact that the longevity of this potassium-source (KNO₃) is very short, nitrates in this type of fertilizer are not desirable during this period.

Given the fact that we can hardly use chemical aids against fungi, the vitality of our turf is even more important. This means that we should try to minimalize nitrates in the first place. Too high a nitrate supply promotes weak and disease-prone turf. Additionally, we must continue to monitor the nutrient balance of the soil for the right elements available for the grass. Elevated levels of Potassium can have a negative effect on the uptake of Cal-Mag. Using Potassium Sulphate is in this case a good option, because this source will become available slower than Potassium Nitrate.

Some fertilizer companies will actually offer a (polymer) coated version of Potassium Nitrate for this reason. However it is our view that only for durations of longer than 4 months there is a benefit to have coated Potassium, such as in plant-nurseries. Coating Potassium Nitrate with for shorter duration applications is a serious increase in costs, which can be avoided by simply using Potassium Sulphate, which will give a duration of approximately 3-4 months as well.

In Fertigation applications, water soluble forms of Potassium Nitrate do have a benefit, namely the high level of solubility. However for application on turf, we will always advice to coat the nitrogen to get a longer duration and less lixiviation of elements. Especially with Potassium, this will increase any imbalance of cations which will result in stressed turf and stunted growth.

Stefan Hoefnagel – Technical commercial responsible at Mivena