Ag 101 Week 44

Potassium – Quality vs. Quantity

Last week was not my best post. Sorry. I explained how I haven’t been feeling the best and frankly writing on a good day is hard enough for me. It’s harder yet on days where I pretty much want to go back to bed.

I’m thankful to be in a position in life I can set my own pace, make my schedule, and I have supportive friends, family, clients, and followers.

According to the doctor, I’m not dying. I needed a different medication to reduce the inflammation and eight weeks of therapy. I’ve also decided to make a few more modifications to my diet to keep improving my health and help elevate the grouchy disposition I have had lately.  I’m giving up coffee; it might get worse before it gets better.                 

Enough with the pity party, now let’s talk about potassium!

I have to admit, potassium (K) is one of my favorite nutrients to talk about. I’m pretty sure it’s because it is a quality vs. quantity factor. I often refer to it as the dessert part of a meal for your plants, and let’s face it that’s my favorite part of the meal. Rely on nitrogen and phosphorus to push yields, but hand it over to potassium to develop kernels, fruit, and blooms. To top off my love affair with it, some of my favorite organic inputs are sources of potassium.

One of the best resources I have that talks about potassium is the Soil fertility Manual published by the Potash & Phosphate Institute of Canada.  I find it to be a valuable resource for soil fertility in general as well.

Here are a few things potassium plays a role in-

1.      Helps ionic balance in plant cells

Ionic balance is the relationship between cations and anions. Which leads to turgor, known as the pressure within the cell wall of a plant that keeps it from wilting.

2.      Helps a plant to overcome diseases

3.      Help a plant to over winter

4.      Helps with optimizing enzymatic systems that regulate plant growth

5.      Helps develop fruit quality, size, taste, color, and storage length

Potassium can be a difficult nutrient to manage in a sense it is not particularly mobile in the soil, except sandy or high organic matter soils. It also has an interesting relationship with calcium and magnesium making it a nutrient of particular concern in forages. Too much potassium can slow down bacteria develop in the gut of a rumen. Too little can lead to fertility issues. My dad is the animal nutritionist, and I’m the agronomist. We have a long-standing conversation about how to balance potassium for optimal plant health vs. animal health. He politely reminds me agronomist are notorious for being cow killers. Since certain crops like alfalfa are considered luxury consumers of K, meaning they will utilize considerably more than they need, much like when I eat cheesecake, the plant will take up as much as you put down. This will produce a great crop but not necessarily healthy for your animals. I can also hear him repeating, “ Alfalfa, Medicago sativa L., is the queen of the farm. Treat her well and she’ll treat you well.”

Thank you, Dad, for keeping me in check.

Potassium exists in three forms in the soil-

Unavailable- This is the form found in the mineral fraction of the soil. It takes the process of weatherization to release and is therefore only available in the soils that are in regions that are well weathered. They are often depleted due to miss management.  

Slowly available- This form is fixed in layers of potassium silicate clays such as greensand. As the clay shrinks and swells during dry and wet periods the potassium is slowly released.

Available- this form is found in the soil solution held by the cation exchange capacity -the fraction of the soil made up of organic matter and clay- but can only account for about 10lbs/acre or less of available K to the plant. Definitely not sufficient for a growing season.

What are some organic sources for potassium-

Manures- Typical analysis 1-3% Medium to rapid release

Great source especially sheep and bat guano. However, care needs to be taken that you are not over applying and causing the very issues you don’t want like disease and insect pressure.

Alfalfa, Cottonseed, and Soybean Meal- Typical Analysis 1-2% Slow to medium release

These are an all-around season long suppliers of not only nitrogen, a small fraction of phosphorus, but potassium as well.

Refer back to week 42

Wood Ash- Typical analysis 3-7% Fast acting

I list this one hesitantly, however, feel it should be talked about. It can be a good addition especially to a compost pile that has time to rest. The challenge with wood ash is it is over applied and changes the chemistry of the soil quickly due to its particle size and makeup. The adage, a little goes a long way is fitting.

Sunflower Hull Ash (K Ash)- Typical analysis 34-36% K Availability dependent on mesh size and pH of soil being used in.

Sunflower hull ash is a relatively new product. Although it has some added benefits of having about 4% phosphorus and trace minerals, it should not be used in the soil the has a pH of 7 or higher. It has a pH of 8-10 making its applications limited to particular situations.

 Potassium Sulfate (SOP)- Typical analysis 50-52% Fast acting

I often have greenhouse growers run SOP at certain points of the growing season to help keep the plant producing and yielding a marketable size fruit such as tomatoes and cucumbers. It is soluble and has sulfur which can help mitigate higher pH’s that greenhouse growers are sometimes challenged with.

Granite Dust- Typical analysis 3-6% Very slow release

As mentioned earlier this is a source of potassium that takes weatherization to release the available potassium that is in the matrix of the granite.

Sul-Po-Mag (Sulfate of potash magnesia, K Mag)- Typical analysis 22%K 22%Sulfur 11%Mg Medium to fast availability

Much like SOP, it is relatively soluble depending on particle size.

High K & Low K Seaweed Shakings- Typical analysis ~27% High K, ~5% Low K

Generally used as a component in a fertilizer blends.

Kelp- Typical analysis 4-13% Slow to medium release

Kelp can be used as a liquid concentrate, powder, or meal. It can be attributed for being part of all five of the previously listed roles K plays in plant health. If I was reduced to recommending one product kelp would be it. That being said you still need to use it judiciously as to not decrease its efficacy.

Refer to week 22 & 38 for more specific uses.

Greensand- Typical analysis ~5% Very slow release

I could list other clay-based materials as well. However, greensand is my favorite, especially considering what it is capable of while being a good source of K and trace minerals. When I got into organic agriculture and was working for a fertilizer company, I had never heard of anything like greensand. They would explain greensand as being magic. It could loosen tight soils and tighten loose soils. Not being satisfied with the supernatural explanation, I came to learn the power of greensand is in the structure. It has a unique layered structure unlike any other clay giving it the ability to correct a variety of soil structure issues. Hands down I would use greensand before any others. I often recommend a 50/50 mix of greensand and kelp.

Refer to week 28 for a brief overview of clays


Greensand & Kelp

Greensand & Kelp