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Soil pH Impact on Potassium Retention

Soil pH impacts potassium differently than other nutrients. For phosphorus, soil pH affects the chemical form of the nutrient and the cations it bonds to. For potassium, however, the impact of soil pH is entirely about finding a place on the Cation Exchange Capacity (CEC).

Not all cations (positively charged ions) are created equal. The affinity, or lyotropic series, defines how strongly cations are held by the CEC. Assuming all cations are present in equal amounts, aluminum and hydrogen will bind to the CEC first, and sodium last:

Al³⁺ > H⁺ > Ca²⁺ > Mg²⁺ > K⁺ = NH₄⁺ > Na⁺

Aluminum and hydrogen have a high affinity for the soil CEC. At a low soil pH (below 5.5), aluminum becomes soluble and exchangeable, and the hydrogen concentration in the soil increases. At these low pH levels, these cations dominate, leaving little space on the CEC for the retention of potassium, ammonium, and sodium. (Sodium’s inability to bond strongly to the CEC is actually a good thing, as it leaches away).

High soil pH levels are created by the presence or application of calcium- and magnesium-based carbonates and bicarbonates. Calcium and magnesium have very similar affinities for the CEC, and both are much stronger than potassium, ammonium, and sodium. At high soil pH, calcium and magnesium dominate the sites bound to the CEC, again leaving little space for potassium retention.

Additionally, the typically low CEC of sandy soils reduces the chance of potassium finding a binding site. The structure of organic matter CEC is also not conducive to the retention of potassium at any soil pH.

In summary, the impact of soil pH on potassium is not about changing the form of the nutrient to limit plant uptake; rather, soil pH impacts the soil’s ability to retain potassium and prevent it from leaching down through the soil profile.

Biologicals and Nutrient Use Efficiency

As crop fertility inputs increase, the need for using soilborne nutrients more efficiently increases as well. This is not a new concept and occurs naturally without prompt. The soil is full of biological processes and is continuously converting organic substances to inorganic, or plant available, forms. There are, however, products in the marketplace that try to add to the native soil biology with varying success.

To better understand how biological organisms use, convert, neutralize and upcycle nutrients they must be categorized and uses described. According to Cornell University, the different types of biologicals, or microorganisms, are best described as living and non-living. The living microbes may include nitrogen fixing bacteria and decomposers. Nitrogen fixing bacteria are microorganisms that can convert dinitrogen from the air using an enzyme called nitrogenase. Nitrogenase is very sensitive to oxygen exposure and needs an anaerobic environment to convert dinitrogen to ammonia. Decomposers simply break down organic matter and residue into available forms of nutrients. The microbes that consume organic matter and residues consist of bacteria, fungi and actinomycetes.

Each type serves a purpose in the process. Bacteria need warm soils and nitrogen to consume simple forms. Fungi and actinomycetes break down cellulose and lignin which take the longest to recycle. This is why residue worked in with tillage tools too deep may not break down for several seasons because fungi need oxygen to work. To make residue cycling quicker, it just needs more soil to surface contact. This can be done by utilizing chopping corn heads/aggressive knife rollers, crimpers/rollers, and tillage practices to name a few.

The non-living section of microbes are derived from living organisms and used as bio-stimulants. Humic and fulvic acids and sugars aid in the processes of residue and organic matter conversion. Living organisms need a multitude of factors to align to reach their full potential. Certain requirements must be met depending on the type of microorganism they are. Perhaps this is why research and yield data has been inconsistent, across the marketplace, for biological additives for cropping systems.

 As mentioned above, some microbes prefer oxygen and cool temperatures to perform their best. So, when introducing a live, or dormant, biological to the soil and/or plant what precautions are being taken? This may require climate cooled storage facilities with aerators for long-term shelf life and quick application windows. Others prefer no oxygen and warmer temperatures. In this instance, knifing (or subsurface application) of a bacterial application may be necessary. Most soils already contain necessary biological life. They may just need better fundamentals like moisture, air, organic matter and nitrogen.

Cornell University Nutrient Management Spear Program. (n.d.). Nutrient release from organic materials (Agronomy Fact Sheet #127). Cornell University College of Agriculture and Life Sciences.

The ALGL Customer Photo Calendar is Back!

The ALGL customer photo calendar is back! Once again, we are reaching out to the best customers a business can ask for.

 Do You have photos to share?  Please share with us pictures of those things in life sciences that speak to you and show how amazing the world around us truly is. We want to see pictures that illustrate what fuels your passion for life sciences and customer service. When you get that picture captured, send it to news@algreatlakes.com along with your name, address, and brief note about the picture(s). Please submit your pictures in the highest resolution possible before September 15th. Then we will select our favorite pictures, then we will be letting our followers on Facebook vote on their favorite, to be on the cover of the 2027 calendar. Follow us on Facebook for voting details.

 Photo criteria 

• Landscape oriented photos preferred but not required.
• Please do not crop the pictures before submission.
• Please share the highest possible resolution photo.
• Please try to avoid company logos and easily identifiable faces.
• No dangerous or illegal activities.

Rules 

• Photo submission deadline is September 15, 2026
• One entry per person, however you may submit more than one photo.
• Must be 18 years or older to enter.
• Need not be present to win.
• No purchase necessary.
• Submitting a photo gives A&L Great Lakes permission to use the photo for promotional use.
• Employees of A&L Great Lakes Laboratories, Inc. and their immediate families are not eligible for prizes but may submit photos for consideration in the calendar.
• Use of images in promotional items does not increase your odds of winning a prize.
• Contest decisions and/or judgements by A&L Great Lakes Laboratories, Inc. are final.

What’s the Difference Between Lawn & Garden and Routine Soil Test Packages?

As the weather begins to warm up, people start getting antsy about their outdoor hobbies such as gardening and lawn care. Many home landscape enthusiasts start each growing season with a soil test. While anyone is welcome to send samples to us directly, many samples often come through our traditional agricultural clients as people want their samples shipped in by the company that they plan to buy fertilizer from. This situation frequently raises the question as to what is the difference between our Lawn & Garden packages and the routine packages used for agricultural samples?

As far as the laboratory processes being used, there is no difference. There are 2 options for Lawn & Garden packages, a basic and a complete package. The basic package is the same as our S1 package. The complete package is the same as our S2 and S3 packages. The difference is the level of fertilizer recommendations included. For Lawn & Gardens, the recommendations are given in pounds of nutrient per 100 and 1000 square feet and product specific recommendations are written by one of the ALGL staff agronomists, i.e. “Use 20 pounds of 21-0-0-24, ammonium sulfate, per 1000 square foot of garden.” These test packages are intended for homeowners who may not have knowledge of calculating fertilizer rates.

What many of our more traditional agricultural clients don’t realize is that we can provide the provide the same recommendations for lawns, gardens, flowers, etc. Using our routine test packages. The difference is that it only includes the calculated nutrient requirements, and not the product specific recommendations. This allows the retailer to choose the most appropriate fertilizer that they offer to meet their needs. When the products are being made by the lab agronomist, we often use very generic products so the homeowner has a better chance of finding them at a big box store or at a specialty garden store.

When using our routine soil test packages for lawn and garden type samples we will change the format to a graphical representation of the soil test ratings to help give the end customer a better understanding of the results. Below are examples of the different report formats.

Lawn and Garden report with product recommendations. 

The Role of Soil pH in Phosphorus Dynamics

Soil pH dictates various aspects of soil fertility. For phosphorus, soil pH impacts the chemical form present in the soil. As soil pH increases, the concentration of hydrogen ions decreases; likewise, the number of hydrogens associated with phosphate decreases.

Iron Fixation in Highly Acidic Soils

At soil pH levels below 3.0–4.0, the predominant form of phosphate in the soil is H₃PO₄. This form is not plant-available and has a high chemical reactivity with iron. This low pH also greatly increases the water-soluble of iron, which creates ideal conditions for the two to bond.

·        Oxidized Iron Soils (Red Clay): If the iron is in an oxidized state, the bond is very strong. This creates an insoluble mineral that has extremely low solubility and plant availability. Soil pH adjustments have little to no effect on releasing phosphorus bonded to oxidized iron.

·        Reduced Iron Soils (Grey Clay): If the iron is in a reduced state, the bond is also very strong but maintains a low level of water-solubility.

Aluminum Interactions and H₂PO₄^- Availability

As soil pH increases, the predominance of H₂PO₄^- increases, which is plant-available. The concentration of H₂PO₄^-starts at a soil pH of 3.5–4.0, peaks at a soil pH of 5.5–6.0, and ends at pH levels above 6.5–7.0. This form has limited reactivity with iron but is reactive with aluminum. Aluminum water-soluble occurs at soil pH levels below 5.0–5.5. The peaks of availability/ water-soluble between H₂PO₄^- and aluminum do not quite align. Additionally, as aluminum is included with iron, or replaces iron in the reaction, the water-soluble and plant availability of the resulting mineral increases slightly.

The "Sweet Spot" for Phosphorus Availability

Between pH 6.0–7.5, phosphorus exists as either H₂PO₄^- or HPO₄^2- _, both of which are plant-available, and the reactive partners of iron and aluminum are not water-soluble. This results in the optimal pH for plant-available phosphorus, with the lowest rate and severity of fixation due to the formation of insoluble minerals.

Alkaline Soils and Calcium Fixation

It is not until soil pH levels rise above 7.5 that HPO₄^2- is the prevalent form and excessive calcium drives the reaction of phosphorus with calcium. High soil pH is caused by the over-application of lime or naturally high calcium carbonate content in the soil. Because high soil pH and high calcium levels are strongly correlated, calcium is often confused with soil pH. The mineral formed in this environment between calcium and phosphorus closely resembles the rock phosphate mined for fertilizer production, which has low water-solubility. The amount of phosphorus participating in this reaction continues to increase as soil pH increases.  However, calcium phosphate minerals are more water-soluble than the minerals formed at a low soil pH. Like the mined mineral, the bond between calcium and phosphate can be broken by acidifying the material, leading to a significant increase in water-solubility. Acidic root exudates are effective at breaking this bond, leading to increased plant availability.

Comparison of Phosphorus Fixation by Soil Environment

How to Dial in a Nitrogen Rate for the Upcoming Corn Crop

The current economic conditions for corn producers require making wise decisions when it comes to crop inputs. One of the higher costs associated with a corn crop is nitrogen (N) fertilizer. Knowing exactly how much you need to purchase can help lock in better prices with early purchase options before the prices are likely to go up as the growing season approaches. Here is a list of things to consider when determining an appropriate N application rate.

Potential Yield – Determine a realistic yield for your operation. This is probably not the year to aim for record yields. Use the average of the last 5 to 10 years of actual yield averages, not just the average you hope for. Consult your seed company agronomist to see how different varieties have yielded in local plot trials.

Nitrogen Use Efficiency – This is the amount of N it takes to produce 1 bushel of corn. Every bushel of corn contains approximately 0.67 pounds of N. However, a corn crop takes up approximately 1.0 pounds of N for every bushel produced. If N can only be applied before planting, generally 1.2 to 1.4 pounds of N per bushel should be applied to account for the greater risk of loss. In a typical system with starter N and sidedress, aim for 1.0 to 1.1 pounds per bushel. If you have the option for late season applications (VT and later), it is possible to reduce rates to 0.7 to 0.9 pounds per bushel.

Maximum Return to Nitrogen (MRTN) – This is a model developed by multiple universities using N response data to calculate the economic optimum N rate for your situation. You begin by selecting your region then entering your expected price per bushel and your cost per pound of N. This model is accessible at https://www.cornnratecalc.org/.

Estimated Nitrogen Release (ENR) – You can use the organic matter from your routine soil tests to help reduce your N application rate. For every 1% organic matter, you can estimate that approximately 20-40 pounds of N will be mineralized or naturally released by the microbes in the soil. However, this is heavily dependent on the weather. So, it is advisable to stay on the lower end of the range.

Presidedress Soil Nitrate Test (PSNT) – Collect a soil test prior to a sidedress application to see how much nitrate has been mineralized by the organic matter. For sampling instructions and data interpretations please see our fact sheet, PSNT for Corn.

Soil Compaction Fundamentals

Soil compaction is often associated with its physical properties. It is when soil particles are pressed together and pore space is decreased. Pore space can account for fifty percent depending on soil type. This can be physically altered through natural and mechanical influences.

In the pore spaces of soil, water and air are in a constant back and forth balance. As soil solution increases due to precipitation weather events or capillary action, there is less air present in pore space. Contradicting this, the soil dries from lack of precipitation and more air is present. Water infiltration and capillary action are affected by soil type and soil compaction.

There are soil types that naturally are more resistant to compaction. The higher the sand content, usually, the less compaction occurs. Soils with more clay tend to compact more and further in depth. They have a higher water holding capacity, smaller pore space and tighter particle bonds.

Compaction can occur at various levels in the soil profile. Tillage practices can influence many compaction points, but on the soil surface it experiences multiple situations. How can some no-till fields have such a hard top layer? Heavy rain events cause lots of surface compaction. What can make this worse is a seedbed preparation tillage pass before such event. This will cause crusting of the soil surface with little pore spacing for germinated seedlings to emerge.

Each pass in the field, whether it be from machine or foot, compresses the soil limiting pore space and compacting as well. A tool to help measure these actions is a penetrometer. It is a solid probe with an indicator dial on top that is pressed into the soil. As it travels through the profile, the needle on the dial will show what the PSI is at the probe tip ranging from 0-300+. Using a ¾ inch tip, 0-200 is considered optimal, 200-300 roots are restricted and anything over 300 is very compacted.

Plow layers, or subsurface compaction, is caused by smearing of the soil and done on a routine basis. These can usually be found around 7-9” deep depending on the region and tools used. These are also mistaken for soil horizon changes. Such as Topsoil A Horizon, to Subsoil B Horizon as soil changes from higher organic matter to structureless massive soils with an anerobic environment.

To manage compaction, it starts with limiting soil surface exposure. Leaving residue or practicing minimal tillage. Not applying too much down pressure with the planter gauge wheels, proper tire inflation or the use of tracks, and not disturbing the soil when field conditions are marginal to saturated.

SoilTrak Rides off Into the Sunset

Last September, the ALGL Client Portal was introduced to provide laboratory business account holders with single sign-in access to existing lab tools, alongside new and enhanced features designed to make doing business with us more convenient. 

eSub, located within the ALGL Client Portal, allows for the online creation of soil submission forms and bag labels. This feature replaces SoilTrak with a cloud-based version that is no longer limited to a single PC. Because eSub and eDocs are integrated, data from past sampling events—including growers, farms, and fields—is readily available for new submissions. Future updates will expand these tools to include additional materials.

After May 31, 2026, ALGL will cease technical support, software updates, and new installations for SoilTrak. While current installations will remain functional, they will no longer be supported.

Plan a Budget and Stick to It

It is no secret that the current agricultural economy is not doing producers any favors as another growing season approaches and crop input decisions need to be made soon. In order to survive these challenging times, it imperative that growers have a firm understanding of their input costs and build a plan to maximize their return on investments and stick to it.

To begin, all input costs need to be identified and divided into two categories, set costs and flexible costs. Set costs are things such as land/rent payments, taxes, interest on borrowed money, equipment costs, etc. There is little to nothing that can be done to lower these costs, so any savings need to be made on other inputs.

The first decision is what crop should be grown? While most producers will decide between corn or soybeans, this may be an opportunity to explore other crops such as wheat or other small cereal grains if there is a market for them in your area. It is important though to consider all impacts of trying a new crop such as equipment compatibility, access to crop protection chemicals, and transportation.

What seed variety should be grown? Work with your local seed agronomists to determine what varieties perform well in your area. While yield is important, the highest yielding varieties may not be the most profitable because they often require additional inputs to produce the highest yield. Look for varieties with a good record of resistance to pests and diseases that are known in your area and don’t pay for traits that are not needed.

Crop protection inputs (herbicides, fungicides, insecticides, etc.) need to be planned and budgeted in advance. This is where previous years of crop scouting can really help. You can generally assume the same weeds and diseases that were a problem over the last few years will likely be again. Budget for a worst-case scenario and use crops scouting and integrated pest management strategies to determine when an application is needed to get the most benefit from the application.

Soil fertility inputs need to be determined from recent soil test data. Ideally less than two years old. Identify what nutrient or other factor is the most limiting. If your pH needs to be raised, liming should take priority over fertilizer. pH determines nutrient availability. So, if the pH is off, the efficacy of your fertilizers is jeopardized. Determine if phosphorus or potassium is more limiting. Phosphorus fertilizers are much more expensive currently. So, at a minimum try to maintain phosphorus levels rather than build them up and certainly avoid applications where soil tests are high. Potassium fertilizer is currently more affordable and potassium soil test levels can drop much more quickly than phosphorus. If the budget only allows for phosphorus or potassium, prioritize the potassium.

The two most important things a grower can do in these tight times is first, do not try to do it all on your own. Rely on advice from industry agronomists, independent consultants, and grain marketing specialists. Second, stick to your plan. Don’t make any rash decisions that could lead to a complete crop failure. Don’t look for a silver bullet, there is no single product or practice that is going to save a poorly managed crop regardless of how good the sales pitch is.

Potassium Availability

Certain plant nutrients must go through biological, chemical and physical cycles to become plant available.  The potassium cycle is much simpler.  Many mineral soils contain a surplus of potassium.  However, much of this is not in the soil solution but held tightly in parent materials like micas and feldspars.  For these to become plant accessible, they must first weather.  As they naturally break down, potassium on the outside edges goes from nonexchangeable to available forms in the soil solution for plants to utilize.

Potassium, being a macronutrient, is taken into the plant in rather large amounts.  This amount can vary from 5-10 times the amount of phosphorus.  As vegetation begins to wither and die, also known as necrosis, potassium is released from the plant back to the soil.  Unlike other residue cycling, K is readily available through this process.

There are four key locations for K in the soil.  In primary mineral structure (unavailable), nonexchangeable K in secondary minerals (slowly available), Exchangeable K on soil colloids and K soluble in water (readily available).  This makes 90-98% of all soil K to be unavailable to plants.  As mentioned above, weathering is the solvent action of carbonic, organic and inorganic acids as well as acid clays and humus.  Weathering must occur to make exchangeable K from parent materials.  Some plants with finer root structures can access this nutrient between clay layers, but many row crops cannot.  The amount of K fixed depends on the nature of the soil colloids, wetting and drying, freezing and thawing and the presence of excess lime.

There are soil types that are difficult to change soil test K values.  A few clay types are Illite (mica-type clay), vermiculite, smectite and kaolinite.  Illite (Drummer, Flanagan, Sable) has the highest K content of common clays. K sits between the layers and is slowly released and has a good long-term K supply.  It can also fix K if soils become dry or compacted. Vermiculite (Graymont, Alida, Iva) has a high CEC and can hold lots of potassium.  It also has a higher fixing capacity than Smectite. Smectite (Patton, Wabash, Toledo) has a high CEC but less inherent K.  This type is a great reservoir for soil K but not a great direct source.  Kaolinite (Bluford, Berks, Gilpin) is a 1:1 clay.  It has a low CEC, poor K retention and needs frequent K fertilization to meet crop demand. 

Potassium cycling is a dynamic equilibrium.  As soon as the plant takes in K, more is released back into the soil solution from exchangeable K.  A plant may take up more K than necessary, called luxury consumption, and this does not directly increase yield.  Potassium applications vary greatly on crop type, soil type, region and residue management.  If the soil test K levels cannot be achieved because of fixation, pH and other soil influences then applications may need to be more frequent to keep up with crop demand.

Source: Brady, N. C., & Weil, R. R. (2016). The nature and properties of soils (13th ed.). Pearson Education.