Quick and Dirty on Plant Nutrition - Potassium to Magnesium Ratio
The K to Mg Ratio: What it is and why it’s important
The Albrecht Method is a sometimes controversial approach to soil fertility that uses base saturation, which is the percentage of the cation exchange that base cations (potassium, magnesium, calcium, sodium) take up in the soil, to determine fertilizer application rates that is the starting point of the K:Mg ratio. While using the Albrecht method solely to approach fertility may not be recommended, it can be used in conjunction with other parts of a soil test such as pH and nutrient levels, and other tools such as nutrient uptake by crop and removal to get best possible fertility recommendation to growers.
What is the K:Mg Ratio?
The K to Mg ratio is taking the base saturation of potassium and dividing it by the base saturation of magnesium.
Eg: A soil test with 4.5% K and 18%Mg means 4.5/18 = 0.25. This means the ratio is 0.25.
What does it indicate?
The K/Mg ratio can be indicative of how available the potassium and magnesium are in the soil. If for example your ratio is less than 0.25, it typically indicates that the magnesium in the soil is over powering the potassium in the soil making it harder for the plants root system to uptake potassium. If the ratio is <0.35 it can indicate that the plant may have trouble accessing magnesium. There are other factors to consider, such as how the other cations play into this as well, but we will talk about that another time!
What can I do about it?
In many soils across Western Canada the K:Mg ratio is well below 0.25 meaning potassium may be a struggle for the plant to access at all times throughout its growth cycle, even if there is a lot of potassium in the soil!
- Option 1: Increase the amount of potassium (potash) put down in bands.
- Option 2: Look to a foliar potassium application at key growth stages such as herbicide timing in cereals and canola or fungicide timing in pulses. A product such as YaraVita AGRIPOTASH is a great option to tackle this situation with.
These options in combination will provide the highest likelihood of response.
