Published April 27, 2020 | By Mike Petersen
What is it when you consider the third macronutrient that we talk about fertilizers from mineral sources that intrigues you? The element K (potassium) is the one I am discussing here today. Yep for you chemistry buffs: Potassium is a chemical element with the symbol K (from Neo-Latin kalium) and atomic number 19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Its molecular weight is 39.089 and has a positive valence of +1. It is found in crystalline form of orthoclase, predominantly from granitic origin. It also is a precipitate of certain salt mines from Australia and China.
Potassium mining in Western Australia, evaporative process for sulfate of potash salts, K2SO4 Designated as: 0-0-51-18.
So? You ask what are some of K’s dominant functions in a plant whether C3 or C4 metabolism?
Potassium has many different roles in plants:
– In Photosynthesis, potassium regulates the opening and closing of stomata, and therefore regulates CO2 uptake.
– Potassium triggers activation of enzymes and is essential for production of Adenosine Triphosphate (ATP). ATP is an important energy source for many chemical processes taking place in plant issues.
– Potassium plays a major role in the regulation of water in plants (osmo-regulation). Both uptake of water through plant roots and its loss through the stomata are affected by potassium. This nutrient plays a huge role in how the stomata cells open and close throughout each day a plant lives.
– Known to improve drought resistance
– Protein and starch synthesis in plants require potassium as well. Potassium is essential at almost every step of the protein synthesis. In starch synthesis, the enzyme responsible for the process is activated by potassium
– Potassium catalyzes chemical reactions by regulating > 60 enzymes associated with plant growth. Furthermore, the amount of K present in the cell determines how many enzyme-driven reactions can be activated at any one time.
– K is necessary to maintain the function of phloem (the vascular tissue that transports sugars and other metabolic products downward from the leaves) and xylem (the vascular tissue that transports water and nutrients from roots to shoot and leaves) transport systems.
The roles of K in plant health is amazing:
K fertilizer is now known to significantly reduce the disease incidence of stem rot and aggregate sheath spot, and negative correlations were found between the percentage of K in leaf blades and disease severity in rice and wheat. K fertilizer is widely reported to decrease insect infestation and disease incidence in many host plants. A French scientist (Perrenoud, S. Potassium and Plant Health, 2nd ed; International Potash Institute: Bern, Switzerland, 1990; pp. 8–10.) reviewed 2449 references and found that the use of K significantly decreased the incidence of fungal diseases by 70%, bacteria by 69%, insects and mites by 63%, viruses by 41% and nematodes by 33%. Meanwhile, K increased the yield of plants infested with fungal diseases by 42%, bacteria by 57%, insects and mites by 36%, viruses by 78% and nematodes by 19%. I quickly gather from that information that potassium is vital to crop health and should not be taken for granted that certain soil tests values may depict>300ppm K and all is going to be fine and dandy.
Courtesy of: International Journal of Molecular Science; Weng, et.al. 2013
Considering Potassium in Plant Metabolism:
Some scientists have stated and I am one of those, that K is the “Big Sister” to nitrogen in nearly all crops; nut trees, conifers, small grains, large grains ie: maize, peas, lentils, dry beans, garbanzos, sorghums, forages, root crops, vine crops which include tomatoes and so on and so on. For those of you who had a big sister, what did she do with you when you were 1 to 4 or so? Drag you here to there, haul you around by the hand or hand to the back and softly push forward was the mode. For those of you who did not appreciate that you know it was annoying or embarrassing. With K in the plant cells, it smooths the way for N to move into metabolic pathways and get there quickly (a less scientific way of saying the of the protein transport pathways). To the left is a flow diagram of what critical roles potassium plays in all grains.
In a future blog article I will bring out the major players in the microbial world of bacteria and fungi who is at work to make potassium available to the root. For now, chew on this information, I realize there are texts and hundreds of scientific articles covering every side to K in plants and having rudimentary information for today will have to do. Just getting a different perspective on this important nutrient source is the right start. I know I learned a few great points of how I should look at potassium.
We will discuss some of the prime important times to fertilize with potassium. The Fertilizer Institute of Canada retains a great deal of research and data on potassium, you may want to go and look at what they have. Website: https://www.tfi.org/