# Potassium in Alfalfa



## Vol (Jul 5, 2009)

Excellent read from Progressive Forage Grower.

Regards, Mike

http://www.progressiveforage.com/forage-types/alfalfa/higher-yields-and-quality-potassium-in-your-alfalfa-fertility-program


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## rjmoses (Apr 4, 2010)

Interesting that the best time for application is a fall application. I've always applied mine in the real early spring (february-1st of March) because of pre-buy prices.

It's also interesting how little is really available for plant usage.

Very good article.

Ralph


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## hog987 (Apr 5, 2011)

I have been having the problem of high k levels on the feed tests. I only put down 20 pounds per acre. But was getting over 2.8%. Its high enough the daries wont buy my second cut anymore. Most of them just look at high k levels. But as long as your within a 2:1 ratio of k to Ca it should be ok. Or so I have read. Iam pushing close to a 3:1 ratio. I just talked to a guy who was saying my P levels were a bit short and if the plants are short of P they will try to make up for it in increased K uptake. His suggestion was to cut back on my K next year or dont put any on and increase my P.


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## Bob M (Feb 11, 2012)

All of my straight alfalfa will test 3% plus for K and I do not have any problems feeding to our milking cows. I could see a problem with feeding to dry cows. I could be missing something.


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## hog987 (Apr 5, 2011)

Bob M said:


> All of my straight alfalfa will test 3% plus for K and I do not have any problems feeding to our milking cows. I could see a problem with feeding to dry cows. I could be missing something.


What does it test for calcium?


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## Bob M (Feb 11, 2012)

I'll Check


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## shadyoakhay (Oct 23, 2014)

great read.


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## hay wilson in TX (Jan 28, 2009)

Well HERE with our calcaredous soils, way too .

With our calcareous soils, luxury levels of calcium. About 50 CEC I am lucky to get a hay analysis above 2.0 % K.

Dumping potash on alfalfa will bring the down to a farrily reasonable calcium level and the potassium up to maybe 2.0% K

This soil has had P& K dumple on it over the years. I am now hoping to get dome of that back with Nitro Radish cover crop prior to planting alfalfa the following fall.


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## Hugh (Sep 23, 2013)

I have written and have had published many horticultural articles over the years. What I have found is that the editors knew little about what I was saying. In fact, I could have said anything I wanted and probably have gotten away with it. My view is that alfalfa should be kept on a minimal potassium diet, so minimal that K nearly becomes the limiting element for growth. It is known in the literature that alfalfa "luxury consumes" potassium, and will take up huge amounts that waste your money and make cows sick. Also, low K alfalfa is in demand.


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## Vol (Jul 5, 2009)

That is interesting information Hugh....I would be interested in reading more on the subject.

Regards, Mike


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## Bob M (Feb 11, 2012)

I agree with Vol Hugh, sends us some more info. I spend a lot of money on Potash each year and if I could save some money that would be great.


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## hay wilson in TX (Jan 28, 2009)

Well I depend on luxury uptake here. When I can get it.

Now I put out some K going into our Annual Summer Drought. The object is to get the plants K levels high enough to have better water use efficiency.

One thing I have learned is Alfalfa killing alfalfa seedlings is a thing for luxury moisture conditions. With two months of drought we have solid stands of volunteer alfalfa seedlings in an established stand.

The allelopathy thing is not reliable, not in alfalfa.

To do well during drought alfalfa needs somewhere in the 2.72% K in the hay analysis.

If I had regularly occurring 3.00% K I would not bother with potash fertilizers. An Here Thing,,,,,,,,,.

It is all more complicated than I can keep track of.


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## hay wilson in TX (Jan 28, 2009)

It is all so interrelated.

I suspect something is out of whack with normaly 3.00% K levels.

With all the elements there is a loss in yield with too much of any element. Which actually may be reflecting a deficiency in one of more growth factors.

A grad student at Purdue demonstrated there is a yield loss with high P% levels. Adding K increases the yield which lowers the K %.

I expect the same is true for calcium but I have not read of any yield problems with luxury up take of calcium. Not for alfalfa or bermudagrass.

There are never any simple answers. Not really.


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## Hugh (Sep 23, 2013)

Mike and Bob,

I'll go by through the lit I have here and try and find the information and get back to you.


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## Vol (Jul 5, 2009)

No rush Hugh....thanks for the reply....and do so at your convenience.

Regards, Mike


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## Hugh (Sep 23, 2013)

Here are some quotes from UC Davis research on alfalfa. All of this can be found in this book: http://www.amazon.com/Irrigated-Alfalfa-Management-Mediterranean-Desert/dp/1601076088/ref=sr_1_1?ie=UTF8&qid=1420494899&sr=8-1&keywords=irrigated+alfalfa+management

"...The improvement in yield that results from application of fertilizers will result in more rapid growth rates, which is more likely to decrease, not increase, forage quality as a result of increased stem growth and more rapid lignfication of the stem...

...Research in California, Wisconsin, and Oregon has clearly shown that there is either no difference, or a decline in alfalfa quality, when K fertilizers were used on K-deficient sites...

...Alfalfa is well known for luxury consumption of K, where the K concentration of the forage increases without an increase in yield. This is clearly not desirable, either from the grower's point of view (waste of fertilizer with no return), or from the nutritionist's point of view, due to the danger of excess K in the forage. This is a serious problem near dairies, where excess soil K cannot be controlled. This problem has been increasingly recognized, and a niche market for low-K hay has emerged-some dairies will pay $5 to $10 more per ton (907 kg) for such "low- potassium" hay."

The books title is, "Irrigated Alfalfa Management for Mediterranean and Desert Zones." However, the principles of plant growth are the same world-wide. The difference with this book is that in takes into account the dry conditions that affect bailing and also tends to give advice on high Ph soils, variety selection for climate, alkaline irrigation water, etc. Also, this book was put together by 20+ PhD's and I'm sure they want to avoid any embarrassing glitches.

I would be inclined to soil test and tissue test the crop. If high K has been seen, then go a season or a couple of cuts with no or very little K applications and tissue and soil test again. (testing the tissue on the alfalfa in the field, not testing the hay) It is important to note that high fertilization rates will grow more stem than leaves, and the leaves are the most important part for the animal. Finally, alfalfa can become deficient in potassium so don't over-do the starvation diet.


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## hay wilson in TX (Jan 28, 2009)

...Alfalfa is well known for luxury consumption of K, Which is not all bad. In fact we can use this trait to our advantage. where the K concentration of the forage increases without an increase in yield. Maybe and maybe not. If adaquate potassium will prevent winter thinning or Summer Drought Stand thinning it has an advantage. This is clearly not desirable, either from the grower's point of view (waste of fertilizer with no return),

I would rather waste fertilizer and keep a stand for an additional two or so years.

Though I have an advantage with our Annual Summer Drought, where with out adequate growth for harvested the alfalfa will bloom and produce viable seed. This seed then can refresh the declining stand and extend the life of a stand.

Which brings up the great Alfalfa Allotropic action, killing off any seedling alfalfa that is so bold to make a try for the sunshine. Allotropy traits are not a sure thing. As writings away from Forage texts point out. Read about the allotropic effects of cover crops and we will find what I have observed for over 20 years. Allotropy is not a sure bet. Climate, soils, and local moisture has a major effect on this trait.

Now if you want to seed allotropy in action look at curly dock in your hay field.

The improvement in yield that results from application of fertilizers will result in more rapid growth rates, which is more likely to decrease, not increase, forage quality as a result of increased stem growth and more rapid lignfication ( Left the spelling in the original ) of the stem.

When a stand thins is when I see a lowering of forage quality. Seedling stand alfalfa is usually my highest quality hay. Preventing the stand from thinning will maintain quality.

Forage research does provide useful information but the lessons learned may not be for the question asked.

Texas is no exception. They did some nitrogen fertilizer test for bermudagrass hay. Applied Nitrogen from 100 lbs/A/season to 800 lbs/A/season.

But they maintained their standard fertility program for all the other elements, and they used the "Industry Standard" 28 day harvesting interval.

It is my contention that their absolute yield would have been greater if they had also increased the application of ALL the other elements and gone to a 42 day harvesting interval. Maybe even a 49 day interval.

Now I like the use of forage plots to find yield data and quality information, plus tissue analysis as I have heard of in Texas, Louisiana, and Arkansas. Their yield and quality results are not tainted by usual hay harvesting losses.

I havehad a stand of RAM alfalfa from Greatplains Research persist thru 11 seasons. It refreshed it's self two time during that time. If this ground did not heave, crack and swell so much that stand would still be producing after an additional 11 years. But I had to reduce my speed during mowing to 4 mph to stay on the tractor seat.

Do not confuse coincidence for causation.


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## Hugh (Sep 23, 2013)

From my reading on the subject, I gather that alfalfa will take-up large amounts of potassium if it is available in the soil, even if the plant doesn't need it for growth. And, (the literature says) if it takes up too much, the leaf to stem ratio will favor the stems, which will reduce the feed value, in that, the major food value of alfalfa is contained in the leaves. Moreover, cows can become ill if too much is potassium is present in their feed.

The literature also says that there is no gain in the quality of the alfalfa if potassium is applied, (even on K deficient soils) only the yield is improved. If one is growing for a market that doesn't care about the final analysis, (feed value for dairy cows) then potassium ought to be applied in such quanities as to effect the most economic gain to the grower. If you want yield, and there is no concern for the health of dairy cows, (and possibly other animals) then apply the amount of potassium (and other nutrients) that will yield the maximum returns. For example, if $100 of potassium will yield $800 of alfalfa, then do that. If $150 of potassium (and other nutrients, of course) will yield the same $800, then you are over doing it, and you need to find the balance that offers the best ratio of input to return. These things are the intelligent farmer's concerns.

By the way, I am learning myself, I am new to alfalfa, and I know there is a chance I could be misguided. I also know that much of the literature on the subject may be sketchy and will improve as time goes by. However, if a book is written by 20 PhD's, is based on field studies, and it is published by the U of C Davis (considered the best Ag school in the world) and this book states that potassium can be over-applied in alfalfa, and that potassium (K) does not improve the feed value of alfalfa, I pay attention.

My first post in this thread, where I wrote: "I have written and have had published many horticultural articles over the years. What I have found is that the editors knew little about what I was saying. In fact, I could have said anything I wanted and probably have gotten away with it," was not meant to imply I know it all, but to indicate that the article referenced in the first post ought to be taken with caution. In the same way, my post here should be taken with caution. Check out what I have written and inform me and others if I have made mistakes.

Any writer can be mistaken and any web post ought to be taken with a grain of salt. Writers can throw things together in a few minutes to earn $75 for a filler article. I know this for a fact. However, I have never written anything for publication without carefully studying the subject. My views...


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## hog987 (Apr 5, 2011)

This is just my observations on fertilizer. The ground applied phosphate increases the green color of the plant and has a moderate increase in whole size of plant. The potassium seems to increase stem size and height. The foliar phosphate increases leaf size if and only if applied at right time(when plants are no bigger than about 6 inches tall). Now sulfur. It seems to increase whole plant size especially the leaf size. Sulfur also seems to make the whole plant a darker green color.

Now these are just my field observations so I could be wrong or missing something. Still trying to play with my fertilizer to get the best return.


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## hay wilson in TX (Jan 28, 2009)

Great I knes I had something like this in my notes. Problem is I do not have the source not the entire article.

Oh well it is better than my dim recollection.

What K does. K plays a major role in regulating the water pressure and water movement in plants, Ferrie explains. "In field crops, potassium is important for managing water and standability," he says. "When K deficiencies occur, lodging can happen. Photosynthesis and respiration are somewhat controlled by potassium. Because potassium has a role in water movement, it affects the movement of carbohydrates throughout the plant.

"Potassium is the activator in more than 80 essential enzyme reactions within the plant. It's a big part of how a plant manages environmental stress. Fields that are low in potassium tend not to be able to handle stresses, such as drought tolerance, winterhardiness in perennial crops and resistance or tolerance to disease and insects."

In the plant, K is found mainly in the cell sap. Unlike some nutrients, such as nitrogen, K does not form other compounds, but remains as a K ion in the cell solution.

"Potassium is required for cells to maintain internal pressure, so plants don't wilt," Ferrie says.

"A study in a Hawaiian sugarcane field showed 18 lb. of K per acre was more effective at preventing plants from wilting than changing the irrigation cycle from 15 days to seven days.

Potassium plays a role in taking water into plant cells. The positive charges on potassium ions draw in the negative charges on water molecules. If potassium moves out of the cells, it draws water out.

"Potassium also regulates the leaf stomata, the openings which allow water vapor to escape. Potassium moves in or out of the 'guard cells,' drawing water along with it. When the guard cells fill with water, the stomata open, allowing oxygen to enter the plant and water vapor to leave," Ferrie says.

"When water leaves the guard cells, it causes the openings to close. If water leaves the plant faster than it comes in, the stomata close to protect the plant from wilting and overheating.

"The closing of stomata on the bottom of the leaves makes the bottom surface area larger than the top. That's what causes corn leaves to roll and soybean leaves to tilt up during dry-weather periods," Ferrie explains.

K in the plant. Early in the season, plants take in more K than they need at the time and store it for later use. Plants can store K in much greater concentrations than is available to them in the soil solution. (That's a good thing, as we'll explain later.)

If a plant needs more K later in the season, it moves the nutrient from the oldest part of the plant to the newest. The element moves easily because it is in the cell sap. If too much K is pulled from the lower leaves, plant cells get weak, letting disease organisms move in.

"The highest level of potassium should be in the newest growth at the top of the plant," Ferrie says. "You can't scout for potassium deficiency from the road, because the symptoms are down lower on the plant. The deficiency starts at the tip of a leaf and goes down the outside. It's like a burning process. The plant is cannibalizing its lower leaves to supply the newer tissue that is higher on the plant."

When K is removed from storage in the stalk, it leaves empty cells that look like Styrofoam or cotton pith, which is visible when you split the plant. This appearance starts at the ear node and runs up and down the stalk in both directions. Too much of this pithy appearance as corn is finishing pollination and coming into the blister stage indicates a problem.


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## hay wilson in TX (Jan 28, 2009)

Did a search on Ferrie & potash

Potassium is involved in many vital plant processes, including standability and the regulation of water loss. But picking the best timing, rate and method of application all depend on using your soil test correctly.
© Darrell SmithKnow how your fertilizer recommendation was calculated to tailor potassium applications to soil type
The purpose of a soil test is to let your soil do the talking. Understanding what you're hearing and seeing, then dialing in the correct rate of potassium (K) fertilizer based on testing method, leads to a healthy soil-crop-farmer relationship.

"Problems arise when advisers use the same recommendation procedure across different soil test extraction methods," explains Farm Journal Field Agronomist Ken Ferrie. "There are numerous ways to analyze soil potassium levels. You, or your adviser, must understand which testing technique was used in order to interpret the results and formulate an accurate fertilizer recommendation."

K recommendations based on soil test findings can be detailed in the following ways:

parts per million (ppm)
pounds (you can convert ppm to pound per acre by multiplying the ppm number by 2)
ppm or pounds, but adjusted based on the cation exchange capacity (CEC) of the soil
base saturation of cations
ppm, base saturation and CEC

Method 1. The simplest way to make a potassium recommendation is to base it on ppm or pounds of K shown on the soil test. "Typically, this type of recommendation is geared to crop removal, along with building up or pulling back soil test levels," Ferrie says. "The goal is to keep the soil potassium level in the optimum range.

"You can tell if this is the source of your adviser's recommendation by reading your soil test; it will only report pounds or ppm of K, along with the soil's phosphorus and pH levels. If you use computer software to formulate this kind of recommendation, the only thing you'll need to enter will be the K reading from the soil test."

The ppm or pound method has some shortcomings. "If there's a lot of variability in your soils the recommended rate of fertilizer might fall short," Ferrie says. "Most laboratories would say you want somewhere around 350 lb. to 400 lb., or 175 ppm to 200 ppm, of K per acre. But, actually, whether a certain level of K is high or low depends on the soil's cation exchange capacity (a measure of the soil's ability to hold nutrients) or texture class.

"Soils with higher cation exchange capacities need higher potassium levels to ensure sufficient K in the soil solution. For example, 190 ppm K might be excessive in a soil with a CEC of 6; you could get luxury feeding of potassium by the crop.

Some soils might benefit from potassium applications throughout the season, such as at sidedressing.
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"On the other hand, 190 ppm K may be too low for optimum plant growth in a soil with a CEC of 25. We and others have documented this by tissue testing and scouting for deficiencies.

"So a recommendation based only on pounds or ppm only works on a narrow range of soils with limited variability. It is fine if you farm uniform soil, but most farmers don't."

Method 2. The next simplest way to make a recommendation is to look at ppm of K and then adjust the recommendation based on the soil's texture or CEC. "This fixes one of the weaknesses of the first method." Ferrie says. "To do this you have to know the CEC of the soils you farm. You can get the CEC from your soil test or by looking at soil survey information online or in a soil survey publication.

"If you want your soil test laboratory to analyze the CEC of your soils, pull samples by soil type rather than by a standard grid system. You can use the smart-grid system, in which you pull the same number of samples, but adjust the location of the grids to stay within soil textures."

Handbooks published by land-grant universities often contain this type of recommendation, based on ppm K and soil texture or CEC, Ferrie notes. (The more sand, the lower the CEC; the more clay, the higher the CEC.) But some recommend different K levels for various CECs or texture classes, so follow your state recommendations.

Method 3. A third method for formulating K recommendations is to adjust the fertilizer rate based on the soil's base saturation level of potassium. "This involves comparing the base saturation of potassium to the base saturation of magnesium and calcium," Ferrie says. "Most advisers who use this method try to hold base saturation of K between 3% and 5%."

This method also has a weakness. A recommendation made only on base saturation might be inaccurate on low- or high-CEC soils. "If a soil test reads only 85 ppm K, but the CEC of the soil is only 4, the base saturation percentage would be high enough that a K application would not be recommended," Ferrie says. "But with only 85 ppm K, you won't have enough K to meet the demand of the growing crop.

"On the other end of the spectrum, a soil with a CEC of 30 could have 200 ppm K and still not reach the desired base saturation level. In fact, with a CEC of 30, it might not be economically feasible to reach the desired base saturation level. In soils like these, you would need to think about annual K applications, banding and making multiple applications throughout the season, to keep K available as the plants need it."

Another consideration when making fertilizer recommendations from base saturation levels is you must know how the soil test for calcium was conducted.

"While labs can use different procedures to extract K, they all tend to obtain similar results in pounds or ppm," Ferrie says. "But when they use different procedures to extract calcium, they can come up with different results."

Calcium extraction methods are not a concern if your recommendations are based only on ppm K, or on ppm and CEC figures or soil texture from a soil survey, rather than a lab analysis. But they become a factor if you base K recommendations on base saturation.

"Calcium is the biggest contributor in the calculation of CEC," Ferrie says. (See "How Base Saturation is Calculated" on page 39 for the procedure.) "If a lab reports a higher calcium load, both the CEC and the base saturation percentage of calcium will increase. A higher base saturation of calcium causes the base saturation percentage of other nutrients, including K, to go down, because the percentages must total 100.

"Consequently, one lab's results may call for an application of K, while another lab's results indicate optimum soil K levels," Ferrie says.

Consider four factors. The most precise K recommendations for variable soils consider all four factors-CEC, the soil type, the nutrient level in the soil and the base saturation. "That lets you make recommendations based not just on the total amount of potassium to apply, but on the timing and method of application," Ferrie says.

"On soils with a low CEC and adequate base saturation levels of K, but low ppm, we must apply enough potassium to at least cover crop removal, and adjust the timing and method of application," he says.

These soils typically are sandy and subject to leaching. So apply K fertilizer in the spring, close to the time of plant uptake. Consider broadcasting part of your potash and applying the rest in starter fertilizer, at sidedressing and through irrigation systems.

"On very heavy soil, with a very high CEC, low base saturation and high ppm, you may have to band some K fertilizer because it may not be economically feasible to raise the ppm high enough," Ferrie says.

You can avoid many problems in soil test analysis by sticking with one lab, so the same procedures are used every time. "Most labs have their own standards for high, medium and low ratings, based on which extraction procedure they use," Ferrie says.

Then, based on your various soil types, understand the strengths and weaknesses of whichever method you use to calculate fertilizer rates.

How Base Saturation is Calculated
To use base saturation to make potassium (K) recommendations, your soil test must report both CEC and base saturation of cations (potassium, magnesium, calcium and hydrogen). Base saturation is the percentage of CEC composed of each cation. The following steps detail how CEC and base saturation are determined:

Step 1. Using the ppm reading for calcium, magnesium, potassium and hydrogen, and the weight, in mil-equivalents (meq), of each element, calculate how much each element contributes to CEC.

Let's say your soil test reads 2,156 ppm calcium. The meq of calcium is 200.
2,156 ÷ 200 = 10.78

The magnesium reading is 342 ppm. The meq of magnesium is 120.
342 ÷ 120 = 2.85

The K test reading is 280 ppm. The meq of potassium is 390.
280 ÷ 390 = 0.72

The hydrogen reading is 13.6 ppm. The meq of hydrogen is 10.
13.6 ÷ 10 = 1.36

If your soil test includes a reading for sodium (Na on your soil test report), include sodium in your calculation. The meq of sodium is 230.

Step 2. Add the contributions of each element to get the CEC:

10.78 + 2.85 + 0.72 + 1.36 = 15.71 That is the CEC for this soil.

(Note: In this example and in the adjacent story, the term cation exchange capacity, or CEC, refers to a "calculated" CEC, which is used by most soil testing laboratories and in soil surveys. A calculated CEC is somewhat different from a "true" CEC, which usually is used to make environmental assessments.)

Step 3. To determine base saturation, calculate what percentage each element contributes to CEC, by dividing the element's contribution to CEC by the total CEC and multiplying by 100.

For calcium, 10.78 ÷15.7 x 100 = 68.7% base saturation
For magnesium, 2.85 ÷ 15.7 x 100 = 18.2% base saturation
For potassium, 72 ÷ 15.7 x 100 = 4.6% base saturation
For hydrogen, 1.36 ÷ 15.7 x 100 = 8.7% base saturation

Why Calcium Readings Differ

Pulling soil samples begins the process; but fertility planning isn't complete until you and your advisers understand how potassium recommendations are formulated.
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The reason soil testing labs might get different readings for calcium is that there are different ways to treat calcium that is bonded so tightly to other elements or soil exchange sites that it probably is unavailable to plants, explains Farm Journal Field Agronomist Ken Ferrie. Although it sounds like a contradiction in terms, this tightly bonded calcium is often called "free calcium." Some soils contain more free calcium than others.

Some labs use extraction methods that are strong enough to break the bonds of free calcium. It then is counted as exchangeable calcium (which is available to plants) on the soil test. This results in a higher calcium reading than another lab that uses a weaker extraction technique. Some labs use a regression equation to account for the free calcium. However, there is no standard equation, so labs can still get different results.

Here's an example of how problems can arise: Say you farm in Tennessee or Georgia, in an area that has mostly light soils with little free calcium. You send your soil sample to a local lab that handles primarily handles soil from the area. That lab does not run a regression equation because there is little need for it. But if an Ohio farmer, with soils with a lot of free calcium, sends his sample to that same lab, he will get a higher calcium reading than if he sends it to a lab that runs a regression equation or uses a different method of extracting calcium.

Because the calcium reading has the greatest effect on CEC and base saturation percentage,
different labs can get different CEC and base saturation results from the same soil sample. The use of different extraction methods and regression equations also cause labs to have different standards for high, low and medium soil potassium (K) levels. "If you use the same methodology to make a K recommendation for soils that are high and low in free calcium, but you do not use a regression equation, you will have problems," Ferrie says.

For example, Ferrie sent a sample of the same soil to two labs. Both used the same calcium extraction method (Mehlich III), but one applied a regression equation and the other didn't. That led to different readings for CEC and base saturation, as seen below. Lab A found Sample 2 to be in the low K range. But Lab B, which ran a regression equation, reports K in the optimum range.

(Remember, a regression equation is required only if a lab uses an extraction method that measures salts such as free calcium and the end user is making recommendations based on base saturation levels.)

To formulate consistent recommendations, a few consultants and advisers build their own regression equations, for use with soil tests from different labs and for various soil types.

Learn and Profit from Nutrient Navigator

The Nutrient Navigator series focuses on efficient, environmentally sound management of nutrients. The goal is to provide practical knowledge that helps drive yields and profits higher.www.FarmJournal.com/nutrient_navigator

You can e-mail Darrell Smith at [email protected]


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## Hugh (Sep 23, 2013)

Here is some more info on P&K from Purdue: https://www.extension.purdue.edu/extmedia/AY/AY-331-W.pdf


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