Potassium – Too Much vs. Too Little: Which is Correct?

Potassium is one of many nutrients that is absolutely crucial for the development of healthy, bountiful crops. Just as carbohydrates, fats, and proteins are macronutrients for humans, potassium is classified as a macronutrient for plants due to its importance. How much potassium is too much, and how little is too little? Research from numerous universities and experts shines some light on this.

How Potassium Affects Plant Growth

Potassium is important to plant growth for many reasons. It is directly involved with enzyme activation within plants, and this includes adenosine triphosphate (ATP) which regulates photosynthesis. Aside from this, potassium aids in moving nutrients and water throughout the plants, assists in opening and closing the stomata, and even boosts persistence through winter when it comes to annual crops. More specifically, potassium:

  • Reduces excess moisture loss and prolongs wilting;
  • Lowers respiration rates, which can preserve energy;
  • Boosts protein content in plants;
  • Aids in the protection against numerous crop diseases;
  • Enhances the richness of starches in grains;
  • Boosts the proper translocation of starches and sugars; and
  • Improves the growth of quality roots, which helps with drought resistance.

The Effects of Too Much Potassium

Despite potassium’s obvious benefits to plants, too much of a good thing can be problematic. Dr James Murphy, a turf management specialist at the Department of Plant Biology and Pathology at Rutgers University, says that too much potassium can boost growth substantially in golf courses, which leads to extra maintenance. Dr. Murphy also says excess potassium can cause salt burns and even negatively affect water features. Too little potassium can cause grasses to perform poorly by reducing the capacity for photosynthesis. This can lead to browning and ultimately grass death.

When it comes to crops, the signs of potassium deficiency vary. The most noticeable sign of deficiency is stunted growth and small yields across all crops. Corn may appear scorched along the edges, and root development will most certainly suffer. Perennial crops like alfalfa will die off during the winter without proper potassium, and with broadleaf crops like cotton or soybeans, leaves may shed themselves entirely and lead to complete defoliation. Too much potassium, on the other hand, disrupts the uptake of other important minerals like calcium and nitrogen leading to deficiencies affecting plant health. Calcium deficiencies cause irregularly-shaped leaves and blossom rot, and nitrogen deficiency causes excess yellowing and perhaps even plant death.

Determining the Right Amount of Potassium

Different crops have different potassium needs and depending on where you grow or maintain your turf, soils contain potassium in different concentrations, too. In order to determine how much potassium you should add to your soil, the first step involves proper soil testing. Then, refer to resources that show the average uptake of potassium for different crops, compare this to your soil testing results, and add enough potassium to make up the difference. It’s important to note that potassium fertilizers come in many different forms, and each one contains potassium in different concentrations.

Determining potassium requirements and ultimately ensuring your soil has just the right amount to support your chosen crop is important for plant health and yields. Too much or too little can be detrimental in different ways, as well. When fertilizing, consider the plants’ uptakes and the potassium concentration of the soil, then apply fertilizer in such a way that the plants’ individual needs are met.