Key Questions to Ask When Ordering Potassium Fertilizer

Alan Blaylock, Ph.D.

Alan Blaylock, Ph.D.

Nutrien

Senior Agronomist

Dr. Alan Blaylock brings extensive North American and international experience in nutrient management to the agronomy team. University studies and service as a university extension soils specialist prepared him for a long career in the fertilizer industry. Having managed both domestic and global research and education programs, Dr. Blaylock has a wealth of experience in applying science-based nutrient management principles and products to solving practical questions. Dr. Blaylock earned Bachelor of Science and Master of Science degrees in agronomy and horticulture from Brigham Young University and a Ph.D. in soil science from Iowa State University. He has been in agriculture his entire life — from his childhood on an irrigated farm in eastern Oregon to teaching soil science at Iowa State University to his current role as an agronomist at Nutrien. These diverse experiences helped Dr. Blaylock develop the skills to excel in translating complex scientific principles into practical solutions. Although early in his university studies he explored computer science as a profession, deep family roots in agriculture brought him back to the people and values of his heritage. His career satisfaction comes from helping others improve the performance of nutrients and cropping systems. Dr. Alan Blaylock is a recipient of the Great Plains Soil Fertility Conference Leadership Award. The Fluid Fertilizer Foundation also recognized Dr. Alan Blaylock with the Werner Nelson Award for his outstanding contributions in the development of soil fertility practices and plant nutrition management to increase crop yields for the benefit of North American farmers and consumers

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Potassium (K) is an essential nutrient required by plants in large quantities. Potassium does not become part of the many complex organic molecules in the plant. It moves and performs many of its functions as a free ion, such as regulating plant water pressure, activating enzymes, balancing electrical charges, transporting sugars and starches, and more.1  

Potassium fertilizers are mined from a variety of geologic potassium salt deposits around the world, some of the richest are in the Canadian province of Saskatchewan. The salts are processed to remove impurities and converted to a variety of fertilizers. Two of the most popular potassium fertilizers derived from these salt deposits are potassium chloride and potassium sulfate. The term “potash” is a general term that is often used to refer to a variety of potassium fertilizer salts or sometimes more specifically to potassium chloride, the most widely used potassium fertilizer. Potassium chloride is referred to as “muriate (meaning chloride) of potash” or MOP, while potassium sulfate is sometimes called “sulfate of potash” or SOP.2,3 

The biggest differences between MOP and SOP are from the anion accompanying the potassium. Potassium chloride and potassium sulfate have advantages and disadvantages determined by the chemistry of these salts, their behavior in soils, and the nutrients supplied in addition to potassium.  Both contain essential nutrients required by all crops. Potassium chloride supplies chloride, the ionic form of the element chlorine and an essential micronutrient. Potassium sulfate supplies plant-available sulfate-sulfur. Both MOP and SOP contain a high potassium percentage (60 or 62 percent as K2O for MOP and 50 percent K2O for SOP). The potassium in both fertilizers is in the same potassium form, and both salts are water soluble, though the water-solubility of potassium sulfate is about one-third that of potassium chloride.3 Potassium chloride could be dissolved in water for spray or fertigation applications while potassium sulfate would not be suitable for these applications. 

The biggest disadvantage of potassium sulfate is cost. Potassium chloride is about 40 to 50 percent less expensive per pound of K2O than SOP. The biggest disadvantage of potassium chloride is its high salt index (116 for MOP 0-0-60 vs. 46 for SOP 0-0-50)4 and chloride content. Potassium sulfate is often preferred over potassium chloride for some chloride-sensitive crops such as potatoes, tobacco, some vegetables and fruits, some tree crops like almonds, walnuts and citrus, although these sensitivities are highly dependent on growing conditions, soil salinity, and salinity and chloride in irrigation water.5 Some studies show concerns for chloride may be warranted in some situations, but most studies show little if any difference in field performance of these two potassium sources provided sulfur or chloride is not deficient, and provided the total chloride from soil salinity or irrigation water is within the tolerance of the specific crop.  For example, potato growers often use SOP as the potassium source because of concerns about chloride sensitivity, even though research indicates negative effects of chloride and an advantage of SOP over MOP are not common.6 Anecdotal reports of comparisons and grower experience are varied. 

Chloride affects plants primarily through increasing osmotic potential of soil water. In other words, chloride salts increase the soil salinity which interferes with a plant’s ability to take up water. Even in chloride-sensitive crops, studies and observations indicate crops respond to the overall increased osmotic potential before chloride reaches toxic levels. To understand if chloride in the fertilizer is a specific concern, one must evaluate total salt loads, potassium rate, and growing conditions. 

One can compare the osmotic effect of the two sources by calculating the soil-water salt concentration resulting from applications of MOP or SOP at a given potassium rate and multiplying by the osmotic coefficients for the respective salts. When applied to achieve the same potassium concentration in soil, the osmotic potential of MOP is about 1.3 times the osmotic potential for SOP, but the total salt contribution from either material at practical fertilization rates is still very small. The effect of 100 lbs of MOP per acre (60 pounds of K2O per acre) on the osmotic potential of the soil water is calculated as about 0.1 dS/m, a measure of salinity. To put this in perspective, the salinity threshold at which growth of almond – a sensitive crop – is not impaired is listed as 1.5 dS/m in the saturated soil extract (electrical conductivity of the extract, or ECe, the standard laboratory measure of soil salinity).7,8 The threshold ECe for strawberry, carrot, onion, and common bean, other sensitive crops, is 1.0 dS/m. The amount of chloride added with normal fertilizer rates would usually be well below the injurious chloride concentrations published for chloride-sensitive crops.9 Sensitive crops begin to show leaf injury at 0.1-0.3 percent chloride in the leaf tissue.9,10 Therefore, unless the total soluble salt and/or chloride load in the soil or irrigation water is near or above the threshold salinity tolerance for the intended crop, potassium source effects are unlikely to have any practical consequence. Note that low precipitation rates and deficit irrigation can exacerbate salt and chloride toxicity issues.9,10 If soil or irrigation water salinity is near or above tolerance thresholds, chloride and salt effects should be managed with potash application rate and timing, possible split applications, maintaining appropriate leaching fractions, and substituting some or all of the MOP with SOP.

Some factors that influence whether potassium chloride use presents a potential risk are:

• ECe (measure of salt concentration) and chemical composition of the irrigation water;
• Total growing-season rainfall;
• Fertilizer application timing in relation to the rainy season and planting or growth of the crop;
• Rate of potassium to be applied and if it will be split into multiple applications; and
• Use of deficit irrigation or irrigation amount plus rainfall less than crop need.

While specific examples of MOP vs. SOP comparison studies in sensitive crops are not common in the recent published literature, one recent example for almond production in California is shown below.11  In this study over five years, only one case produced a significant advantage of SOP over MOP – with fan jet irrigation delivery.   

Emerging biostimulant technologies may also be available to mitigate salt effects or increase salt tolerance. Research with some of these materials is showing promise in mitigating or reducing salinity stress. The grower should study available third-party research and do on-farm tests with these products before large scale use. More research is needed, but some early returns from the research being done indicate these products could facilitate additional management options. 

You know it’s time to fertilize your lawn, so you head to the store. As you walk through the fertilizer aisle, you notice three numbers on the front of each product. The first reads “23-3-8.” The second one is marked with “24-3-6.” Bags three and four also sport a series of three digits. You aren’t sure what these numbers mean or which seasonal blend your lawn needs to reach its maximum beauty.

Understanding these numbers, buying the right amount of fertilizer, and applying it properly throughout the year will empower you to grow the lawn of your dreams. To get started, here’s what you’ll need to know.

What Do Fertilizer Numbers Mean?

The numbers on the front of your lawn fertilizer bag are a “fertilizer grade”, sometimes called an “N-P-K ratio”, which describes how much Nitrogen, Phosphorus and Potassium it contains. These are three of the most important nutrients for your lawn, and different fertilizers will contain different balances of each.

As the seasons change, your lawn will need more of some nutrients than others to stay healthy and strong. This is why you see a different set of numbers on each of our IFA 4Plus seasonal fertilizers. Let’s look at these numbers more closely and see what they’re doing for your lawn.

Are you interested in learning more about npk 15-15-15 compound fertilizer? Contact us today to secure an expert consultation!

What Are N-P-K Ratios?

It’s important to note that the Nitrogen, Phosphorus, and Potassium numbers on your fertilizer are percentages. For instance, a bag labeled with “23-3-8” will contain 23% Nitrogen, 3% phosphorus, and 8% Potassium. Together, these percentages show the fertilizer’s “N-P-K ratio”. So, what does each nutrient do for your lawn?

Nitrogen and Its Role in Fertilizer

The first number listed represents the percentage of nitrogen in the bag

Nitrogen helps your grass to appear green, lush and thick. Nitrogen aids in the creation of chlorophyll, which is responsible for producing the green pigment in the grass and is the compound by which plants use sunlight to produce sugars from carbon dioxide and water.

Nitrogen or “N” stimulates new root growth. Many early spring fertilizers will have a higher Nitrogen level to give the lawn a kick and get it growing early. It can help turf recover from environmental stresses and injury. An application of nitrogen in the spring, and then timely spreading throughout the growing season will help fortify turf to better withstand environmental stresses such as heat and insects.

The Benefits of Phosphorus in Fertilizer

The second number represents the percentage of phosphorus

Phosphorus is critical in developing and strengthening a healthy root system of turfgrass. If only nitrogen is applied to the lawn, the grass will be nice and green, but as watering or a drought hits the grass will be greatly impacted. Having strong roots in your grass will keep your lawn healthy through the changing weather and stresses of the seasons.

Phosphorus or “P” is a primary plant nutrient that is involved in the metabolic processes responsible for transferring energy throughout the plant. It’s crucial to introduce phosphorus when first establishing turfgrass and continue application as the grass grows. An abundance of phosphorus allows plants to grow more efficiently.

The Perks of Potassium in Fertilizer

The final number is the percentage of potassium

Potassium is important to overall plant health. Potassium or “K” supports the internal process of the plant cells that affects photosynthesis, water absorption, respiration and protein production. A deficiency of potassium weakens a plant and increases its vulnerability to drought, temperature fluctuation injury and disease.

Adding soluble potash (K2O) to the soil helps grass withstand stress, drought, and disease. Specifically, potassium helps maintain pressure in the cells of the plant, resulting in a positive influence on drought tolerance, cold hardiness, and disease resistance.

Achieve the Beautiful Lawn You Desire

The N-P-K ratio in each bag of fertilizer varies from season to season. It changes based on the nutrient requirements of turfgrass for the upcoming weather and temperatures expected for the next 6-12 weeks. In the IFA 4Plus annual lawn care program, steps 1 and 2 establish a foundation for a healthy, weed-free lawn. Then, steps 3 and 4 provide your lawn with a perfect balance of nutrients according to the season.

Fertilizing in Spring and Summer

You’ll notice the fertilizer numbers “25-5-10” on our IFA Spring & Summer fertilizer. A slow release of nitrogen delivers even, consistent feeding throughout hot summer months. Plus, with slightly more Potassium than the previous steps, you’re supporting the lawn’s ability to absorb water, produce proteins, and stay healthy.

Fertilizing in Fall and Winter

Up next, our IFA Fall & Winter fertilizer loses some Nitrogen content, and gains Potassium with fertilizer numbers that show “22-2-12”. This fertilizer helps to continue nourishing your lawn through the milder fall months and boosts its ability to stay strong and healthy during winter months.

IFA 4Plus Lawn Care Fertilizer Program

The IFA 4Plus Lawn Care program is locally formulated and specifically designed to help produce the best results in the Intermountain West. With two of our four applications, we also use Omnicote Technology that allows micronutrients such as Zinc, Iron, and Manganese to coat every pellet of fertilizer and thus getting an even nutrient distribution on the lawn. These elements may not require the quantity of the three major elements, but they are just as important.

When applied in conjunction with each other, IFA 4Plus Lawn Care maintains the rich, deep green lawn you desire each season, while also building stronger, healthier turf for future years.

Let Us Help

As always, let the good folks at IFA Country Store help answer questions when you’re walking through the fertilizer aisle on your next visit. The success and beauty of your lawn is important to us.