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