News

Cutting Phosphorus Fertilizer Applications Without a Soil Test?

The current farm economy has driven a wide range of crop budget conversations. How to produce more with less is the key to the economics for 2025. But the key to that statement is twofold, we need to focus on maintaining and increasing yield while cutting costs. All crop inputs are in the cross hairs, but $800 per ton phosphorus products seem to have a bullseye painted on them.

Phosphorus is key in maintaining yield, so cuts to phosphorus inputs need to be made wisely. The idea of reducing phosphorus rates without a soil test is a recipe for problems, however there are producers looking to do just that. We have all heard of examples of producers getting good yields on soils testing low in phosphorus, so why fertilize? Why soil test?  The answer to this question is in data.

Often in publications, soil fertility data like this is summarized with the red line that leads the reader to think that as soil test phosphorus increases, yield increases. This can be misleading. When reviewing more detailed data, there are soils testing low in phosphorus (left side of the scatter plot) that are yielding near 100% of relative yield, and some at 60%. As soil test phosphorus levels increase (moving to the right), the top end yields do not change much (green line), but the low-end yields (yellow line) increase significantly.

Applications of phosphorus on low testing soils may not always increase yield but can mitigate the risk of low yields. This data also suggests that there is no value in building/maintaining a soil test above 40-50 ppm M3- ICP and soils testing less than 20-30 ppm M3- ICP are still potential candidates for phosphate applications.

A soil test can identify those fields that can forgo an application of phosphorus, and those fields that should have phosphorus applied to maintain yield potential, especially if the spring of 2025 soil conditions challenge early season root development. If you have any questions about phosphorus management, be sure to contact your ALGL agronomist.

Great Lakes Yield Enhancement Network

For growers and crop advisors in the Great Lakes Region looking to improve their wheat production, don’t miss the opportunity to participate in the Great Lakes Yield Enhancement Network (YEN). This program was developed not only to help growers increase yield, but also to improve wheat quality and profitability through collaboration among growers, crop advisors, and university researchers. Now entering its fifth year, this program has grown from about 50 farms to well over 200 and they would like to continue to grow. Many of the current farms enrolled in the YEN are in Michigan, but other states are welcome to participate.

There is a cost associated with participation in this program, but it includes multiple soil, plant tissue, and grain tests throughout the growing season. Each participant is given a detailed report about their wheat production and how many of their own metrics compared to the other participants at the end of the year. What makes this program unique is that it is not purely a yield competition. Growers are encouraged to openly share their practices and observations with other participants.

If you are interested in learning more, please visit greatlakesyen.com. The deadline for registration is nearly here to register for the 2025 season, but will reopen for 2026.

The Right Place for Potassium

For the past decade, agriculture personnel have been noticing the decline of soil potassium levels.  It is no surprise that as the yield potential for crops increases, so does the demand for more nutrients.  In many circumstances, these required removal rates are simply not achieved with current recommendations.  There may come a point where the correct crop removal rate is not affordable, creates too high salt concentration, soils are unable to support such rates, and/or equipment cannot apply these rates efficiently.  Choosing the right place to apply potassium can lend aid is such times. 

Most potassium (K), or potash fertilizers are spread on top of the surface of the soil.  They are generally blended in with products such as DAP or MAP for a fall or early spring application.  Most potassium fertilizers are soluble but do not move in the soil like other applied fertilizers.  This is because K is a cation and much of the soil, primarily clay and organic matter, is negatively charged.  The process of binding soil particles and K is known as adsorption.  This is why it takes the correct placement of the fertilizer.  It would be counterproductive to place a K application where the roots of the desired crop will not be. 

Crop types and rotations should affect applications.  Some root systems can reach deep into the soil profile, while others are shallow and grow more horizontally.  Already stated above, K is not very mobile in the soil profile.  There are many different cropping techniques and systems that all require potassium for a successful crop.  Let’s use corn as an example.  A majority of the K is surface applied as a dry product.  Once the fertilizer has been spread, or blown on, it must be incorporated. 

How fast the applied product gets to the root zone of the intended crop relies heavily on the product used, soil type, precipitation and current nutrient values.  When the product is mechanically incorporated, it is fairly simple to achieve even distribution.  Tillage makes it easier to apply higher rates without experiencing stratification of K fertilizer.  Although it can happen at shallow working depths.  Fertilizer stratification is when nutrients are unevenly distributed.   Often a surface application in no-till conditions will concentrate the nutrients on the surface, rather than in the root zone. 

In a no-till system, surface applied nutrients must be incorporated with water.  This makes it especially difficult when trying to raise pH and applying K fertilizer.  Both are being concentrated near the surface, binding to negative soil particles.  Soils with a lower CEC, cation exchange capacity, will be able to achieve nutrient accommodations lower in the soil profile much sooner than high CEC soils.  Once the exchange sites are full, nutrients like potassium will infiltrate deeper.  If large amounts of K applications are made near newly planted seeds, salt damage can occur. 

A management strategy to combat nutrient stratification, potential erosion issues with conventional tillage and dispersing inadequate rates via broadcast is strip-tillage.  This is essentially banding the product in, or just below, the root zone.  Some describe it as the best of both worlds, but it too has its challenges.  It can require expensive equipment.  Not only the strip-till bar, but the distribution system, meters, rate controllers, plumbing and enough tractor to have it effectively work.  It can also be slow depending on rate, product, soil type and terrain. 

With any potassium application, it is important to implement the 4Rs for the best environmental practices and return on investment.

Lab Questions – Impact on Hydrogen and Calcium Base Saturations When Lime is Applied

A question came to the lab. The base saturation #’s look a little out of whack-averages are: Ca-55%, H-23%, K-4%, and Mg-18%. Avg pH is 5.5 but is fairly uniform. Will a lime app bring the Ca up and the H down?

Keep in mind that the base/cation saturation will add up to 100% and the base saturation values are calculated from the soil test results (ppm or lbs/ac) of these nutrients. In some cases the hydrogen saturation is not reported so the reported numbers do not add up to 100%, but the hydrogen saturation is part of the calculations even if it is not reported. Adding any one of these nutrients should lead to a higher soil test result. These higher results will lead to a larger contribution to the base/cation saturation calculation for the applied nutrient and thus a higher percentage. Since the base/cation saturation must add up to 100%, when the percentage of one nutrient increases, the others must go down.

In addition, the H% is calculated from the buffer pH (or soil pH if calculated from TEC), as the soil is limed, the soil and buffer pH increases, leading to a lower calculated hydrogen percent. The reduction of the H%, leads to increases in the other cations.

The Right Source of Potassium

Potassium, or K, is unique in a way that soils have a relatively large amount in the Midwest region.  Some soils can range from 15,000-20,000 ppm total K.  Even though there are large amounts of this macronutrient, it must be in an exchangeable form.  It is estimated to be only 1-5% is available and most soil contains approximately 1-3 ppm in the soil solution. 

Why is potassium so important?  Afterall, when reviewing commercial fertilizers, it is listed as the third number in the grade or analysis.  The functions of K in the plant are numerous.  It plays a key role in cell growth, photosynthesis, stomata function, enzyme activation, nutrient absorption and water retention just to name a few.  Using corn as an example, K deficient plants can experience marginal leaf necrosis, reduced plant height, poor reproduction and stalk lodging. 

There are multiple variables to consider when evaluating soil K levels.  Weather, residue, soil type and sampling habits can all play a large role in test levels.  Weather will affect the uptake of accessible soil potassium simply by not having enough moisture for uptake.  It is important to understand just because the crop is showing signs and experiencing symptoms of K deficiency, that environment dictates uptake of this macronutrient. 

When choosing the right source of potassium, or potash, do not over think what type of K is correct.  The K is nutritionally the same in all fertilizers.  However, many commercial fertilizers are not only K.  Some crops are sensitive to individual nutrient salts.  There are many soils with insufficient amounts of individual nutrients, and this is why it is important to select the correct type of fertilizer for individual cropping systems, soils and maintenance programs.

Here are some examples of potassium fertilizers and their composition.  Potassium chloride (KCI; 0-0-60) This is the most common for bulk blending and row crop agriculture.  This would not be a good choice for crops such as almonds since they are sensitive to Cl^-.  Potassium nitrate (KNO₃; 13-0-44) is an additional source of nitrogen and a good choice for chloride sensitive crops.  Potassium magnesium sulfate (K₂SO₄•2MgSO₄; 0-0-22) used to supplement magnesium and sulfur with K.  Potassium sulfate (K₂SO₄; 0-0-50-18) has a low salt index and includes sulfur.  Potassium thiosulfate (K₂O₃S₂; 0-0-25-17) is a liquid fertilizer and can be used in sidedress applications in dry conditions.  Potassium hydroxide (KOH; 0-0-75 has a high pH.  Often used as a liquid fertilizer that is absent of chloride and best used in acidic soils.   

Sample timing is critical when accessing K levels.  It is advised to pull samples after the same crop each time.  Soybeans, for example, will release potassium back into the soil much faster than corn.  As soon as the cell ruptures K is released and available.  It does not take a microbial process for availability.  This is why soil test levels vary greatly depending on sampling time and previous crop. 

Extreme, dry conditions can also impact soil test K levels as they become tightly bound to clay particles.  When making management decisions for potassium, always sample at the same time of year, after the same crop type, at the same depth/location and be mindful of current weather/environmental conditions when analyzing data.

Source: International Plant Nutrition Institute. (2012). 4R Plant Nutrition: A manual for improving the management of plant nutrition (pp. 40-41). Norcross, GA, USA: International Plant Nutrition Institute

2024 In Review - A Lab Perspective

Editorial by Agronomist Jamie Bultemeier

It seems as if the past few years have found new and intriguing ways to challenge agriculture. 2024 was up to the task and on par with that trend. This year has brought a wet spring for some, a dry summer and fall for most, and a shortened growing season for all. These challenges have also impacted the lab.

The spring soil sample season began early this year in January. There was a very brief pause between 2023 fall soil sampling finishing up in late December and spring 2024 soil sampling starting in early January. January 2024 produced the 2^nd largest January of soil samples in lab history. January was followed by record February and March sample volumes. The spring rains were just enough to delay planting, but not soil sampling. Strong spring soil sample volumes continued through April and May when in-season sampling began. In season sampling carried the strong soil sample volumes through the month of June.

About the time the spring soil sample season was slowing, plant tissues began. A week or two earlier than normal. There was no break between the two seasons. The rapid fast paced operation of the lab continued without a break at record plant tissue test sample volumes in July.

While soil samples did set more monthly records in the summer months, the lab staff did get a very short, but needed break, in sample volumes in August. However, the break was short lived. The hot dry weather accelerated crop development from north to south in our trade area and the fall soil samples arrived early and without delay. Usually fall soil sample volume ramps up over a 3-4 week period, not in 2024… The lab went from a few thousand to full capacity in about a week. This fall there was no widespread or regional rains to delay or slow soil sampling. The samples came fast, in large numbers, and constantly for weeks. Breaking more monthly sample volume records in September and November necessitating the need for the staff to work several weekends in the pursuit of maintaining a reasonable sample turn time for our customers.

All of the 2024 weather challenges compounded for the lab, yet 2024 was a great year. For the first time since 2020 we had a complete staff, and great fall seasonal staff that stuck with the lab for the entire season along with many that returned from last year. We had amazing support from our customers with unparalleled kindness that grew as the year progressed into fall soil sample season. The positive notes written on shipping box flaps, submission forms, and extra notes shipped with the samples had a bigger impact than you can imagine. We had fun through social media noting the staff’s fondness for candy, and the candy that arrived in sample boxes made the long day easier and gave them more purpose in their work.

Reflecting back on 2024, I sit in awe of what we accomplished in partnership with our customers. While the term partnership is often overused, it is the only term I have to describe the working relationship between the lab and our customers. I can recount numerous examples of the lab and customers working together in full cooperation to meet the needs of our collective customers, breaking records all along the way.

As the year draws to a close, I am reinvigorated with the potential in this industry. The level of professionalism in our customers is outstanding and it only reinforces that we are fortunate to have a great customer base that we can grow alongside.

Weakly Buffered Soils

When adding lime to acidic soils to increase the soil pH, the lime needs to neutralize the acidity in the soil solution along with the acidity released from the soil’s CEC in the process. There is a pool of reserve of acidity on the soil CEC that is released to maintain equilibrium between the CEC and soil solution. The impact of this reserve acidity held by the cation exchange sites will vary depending on the CEC of the soil.

The rate of lime to apply in the goal of neutralizing acidity is determined by using the buffer pH for soils with a CEC above 7, and organic matter below 20%. The buffer pH is a measurement of all acidity in the soil solution along with the reserve acidity held by the CEC of the soil. As soil CEC decreases so does the pool of reserve acidity. Below a CEC of 7 the reserve acidity is small and has little impact on lowering the buffer pH. Therefore, buffer pH is not a good indicator of lime application rate for these soils.

For weakly buffered soils, lime is applied at 1 ton/acre for each 0.3 - 0.4 of desired increase in soil pH, maximum 2 ton/acre. pH adjustments are usually triggered when the soil pH is 0.3 units lower than the target pH for the field.

A weakly buffered soil can have a CEC in high 6’s to low 7’s. To determine if a soil is weakly buffered, calculate lime rate for soils with a water pH of 6.2 or below using the weakly buffered rate above and an equation using buffer pH, use the higher of the two calculated lime rates. For more information on weakly buffered soil, contact you regional ALGL sales agronomist. 

Registration for 2025 Soil Fertility Workshops Is Open!

Dates and locations are set for the 2025 Soil Fertility Workshops. The goal of our workshops is simple: we provide a general overview of fundamental agronomic principles and current university research so our attendees are better able to make nutrient management decisions for their customers or for their own operations. Today’s producers are inundated with information regarding crop inputs and practices. By applying the fundamental principles of agronomy to these inputs and practices, a consultant, agricultural retailer, or producer can evaluate and decide which of those are most applicable for achieving both the short-term and long-term goals of a specific operation.

The workshops are developed and presented by A&L Great Lakes Laboratories’ Agronomy Staff comprised of Certified Crop Advisers, Certified Professional Agronomists, and Certified Professional Soil Scientists whom have a wide range of experience in the agricultural industry.

We will be presenting six workshops in January and February in Illinois, Indiana, Michigan, and Ohio. Registration can be completed online, or by mail/email. Click here for more information and registration.

January 28, 2025 - Fort Wayne, IN

February 4, 2025 - Champaign, IL

February 12, 2025 - Frankenmuth, MI

February 13, 2025 - Waldo, OH

February 18, 2025 - Grand Rapids, MI

February 20, 2025 - Indianapolis (Plainfield), IN NEW LOCATION

Different Sources of Phosphorus

To determine the right source of phosphorus, there are several factors that need to be taken into consideration.  First, a background of this macro-nutrient and how it is utilized in the plant.  Phosphorus, or P on the periodic table, has various states in soil.  It can be fixed, active and/or part of the soil solution.  Fixed P is the largest of pools and is not available to the plant.  The conversion of fixed to active is very slow and has little impact on soil fertility.  Active P in solid phase can be released into soil solution easily and replenishes the soil solution as the plant removes.  Phosphorus in a soluble state, or solution, is the only form for plant uptake. 

The role of phosphorus in the plant starts with being the elemental component of ATP-ADP, DNA and RNA.  These are the energy sources for photosynthesis, and transfer energy/nutrients. P plays an important role in fruit set/development and an essential component of cell membranes. 

Manure and biosolids can supply large amounts of P and is usually a direct reflection of their diet.  Before applying these sources, a laboratory analysis must be conducted for proper rates.  Handling, storing and transport of manure sources can be challenging.  This usually creates more inconsistencies from one sample to another.  There are, however, several commercial fertilizer options that are consistent.

Monoammonium Phosphate (MAP; 11-52-0) is water soluble and makes the pH surrounding the granule reasonably acidic at 4-4.5 pH.  This makes MAP one of the more suitable fertilizers in neutral to high pH soils. 

Diammonium Phosphate (DAP; 18-46-0) is one of the most used P fertilizers in North America.  It has a high nutrient content and is easy to handle/store.  Unlike MAP, an alkaline pH of 7.5-8 is formed around the granule.  Ammonium is released from the fertilizer and becomes volatile.  This is only a concern if placed too close to germinating seeds, is not incorporated, or pH is higher than 7.  As bacteria convert the nitrogen to nitrate, the pH is lowered.

Ammonium Polyphosphate (APP; 10-34-0 or 11-37-0) is comprised of orthophosphate and polyphosphate.  50-75% of the P is in the form of polyphosphate.  This makes the other 50-25% readily available for plant uptake.  What is not readily available, will eventually convert to available in a short period of time depending on the environment. 

Triple Superphosphate (TSP; 0-45-0) has one of the highest P concentrations out of all the fertilizers not containing nitrogen.  Over 90% of the total P is water soluble, making it a good choice for fast plant uptake.  This fertilizer will make the soil solution acidic (pH 2-3) as the granule dissolves.  It is a great choice for blending custom applications.

There are several options for phosphorus fertilizers on the market, and these are just a few of the commercial ones available.  When deciding which one to utilize, always apply based on soil test data, and be mindful of the 4Rs (Right Source, Right Rate, Right Time and Right Place). 

Reference: International Plant Nutrition Institute. (2012). 4R Plant Nutrition: A manual for improving the management of plant nutrition (pp. 40-41). Norcross, GA, USA: International Plant Nutrition Institute

Fall Lawn Aeration

Recently the greater Midwest region has been experiencing drought conditions.  This has not made it easy for lawncare, or annual maintenance, that is usually conducted in the fall.  One positive experience when undergoing times of environmental stress is the possibility to see flaws that are usually covered up, or otherwise hidden.  This is a perfect time to access situations like compaction, low grass densities or poor root growth in yards. 

Once a lawn is established, it makes alterations or “fixing” issues very difficult and time consuming.  The good news is that with the right tools, knowledge and some patience most issues if not all can be resolved.  When scouting a lawn during drought conditions the easiest, and most noticeable, concerns will be the different colors.  What makes turf brown, green or a shade in-between starts with the question, why?  Usually, the weeds will still stay green during times of stress, and the grass will go dormant.  This causes large patches to turn brown and if uniform potentially the whole yard. 

This is when the caretaker will notice the sins of the past as well.  There will be brown, or yellow, areas caused by compaction or poor drainage.  This is from the grass not having a vigorous root system due to poor porosity in the soil, or potentially a hardpan from topsoil being brought in then dumped on hard clays during the construction of structures.  High traffic areas will also show signs of abuse as soil moisture declines. 

Compacted areas are difficult to manage in established lawns, however, depending on how deep the compaction is, it can be amended.  For the Midwest, the freezing and thawing over the winter months helps.  If it is surface or shallow compaction, using a core aerator will promote better root development over time and help increase the amount of air in the soil.  There are several different turf aerator types on the market.  Using a ride-on, hydraulic core aerator will be the best option for depth and getting the largest core size especially during drought conditions.

More than likely, this will not be a one-season fix.   Depending on soil type, grass species and severity, it may take several seasons.  The core aerator will promote soil contact with the surface of the grass.  This helps with the breakdown of thatch.  Thatch is a layer of dead grass located on the soil surface.  It is when grass accumulates faster than decomposed.

Once the lawn has been aerated, this is a perfect time to overseed, fertilize and adjust pH if necessary.  Some of the larger aeration tools allow a 5” core to be pulled.  This enables a perfect area for pH buffering materials to enter a lower profile.  Soil is then exposed, creating better seed to soil contact and fertilizing, for example nitrogen, will promote the breakdown of the season’s thatch as well.