# Waypoint Soil Test Education



## Letterson (May 10, 2018)

Hey all,
I received my first soil test last week and would love some help understanding a few concepts. The report did not include recommendations and I figure it's a good opportunity to learn the ideas and the math.

1. The report states that I could use phosphorus and potassium. Is there a site or location that discusses the optimum range for these and other nutrients?

2. Are there equations to help understand how many lbs/1000sqft is needed to increase k levels (as an example) in PPM? As an example, I have 69ppm in K. How many lbs/1000 in K is needed to get that to whatever the optimum range is? Is there a common equation?

Here is a copy of the report if you're interested, thanks everyone!


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## Ridgerunner (May 16, 2017)

You should be able to find what you are looking for in this thread:
https://thelawnforum.com/viewtopic.php?f=24&t=1088
Within the body of the thread are the recommended sufficiency ranges for each of the different extraction test methods. e.g M# = Mehlich III. Further into the tutorial are the formulas.


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## g-man (Jun 15, 2017)

It is great that your are seeking to learn and understand. The link ridgerunner posted is great. I would suggest you post what is your conclusion/calculations as a way to verify.


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## Letterson (May 10, 2018)

This is incredibly helpful. I am working through the post now and will post my math when complete. @Ridgerunner, this is exactly what I am seeking to learn. Thank you very much.


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## g-man (Jun 15, 2017)

@Ridgerunner

Letterson, when you use the @ click on the blue floating name. That changes it to [ mention] username [/ mention] and the person gets the notification.


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## Letterson (May 10, 2018)

From the test my potassium is 69ppm and if I want to raise it to 159 ppm, the deficit is the 90ppm to be added. 90/1,000,000 (ppm) = 180/2,000,000 lbs per furrow slice of one acre.

If I buy SOP potassium, it contains 50% K20, which is only 83% elemental potassium. Is the conversion factor listed 1.2 just rounding up from 1.17 in this example?

180lbs * 1.2 = 216lbs per acre of K20
216lbs / 0.5 lbs (since only 50% of the bag is K20)= 432lbs per acre of SOP

There are 43.5 thousand square feet in an acre; so dividing 432 lbs/43.5 sq ft = 9.93 lbs per 1,000 sq ft (M).

Does that seem right?

Thanks @g-man & @Ridgerunner


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## Ridgerunner (May 16, 2017)

It will help to label each operation:



> From the test my potassium is 69ppm and if I want to raise it to 159 ppm, the deficit is the 90ppm to be added. 90/1,000,000 (ppm) = 180 lbs of K (Potassium) per furrow slice of one acre.


The conversion factor of 1.2 is actually rounded down from 1.2048192. (1 / .83)

There are 43.5 thousand square feet in an acre; so dividing 432 lbs/43.5 sq ft = 9.93 lbs of SOP per 1,000 sq ft (M).



> Does that seem right?


Yes. :thumbup: @g-man please double check me, thanks.


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## g-man (Jun 15, 2017)

My numbers are slightly different, at 10.36lb SOP, but it is likely due to rounding. It is late and i use a different math approach. The recommendation is apply not more than (NMT) a pound per Ksqft per rolling month. So it will take you around 5 months to get there if you don't loose anything. How could it go away? Bagging your clippings plus normal leaching from the soil. Therefore retest next year and see how much improvement towards the goal of 159ppm.

You have a good soil.


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## Ridgerunner (May 16, 2017)

@g-man I thought recommendations where part of the Waypoint package? No?
@Letterson Can you shed any light on why they didn't provide recommendations?


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## g-man (Jun 15, 2017)

I just opened the North Carolina Form. There is a field to enter the crop, but no footnote for what value to use (e.g. 563 - Fescue Lawn, 533 - Bluegrass Lawn). The forms for TN, VA do have the footnote. If the field is blank, they wont provide recommendations.


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## Ridgerunner (May 16, 2017)

That would explain it. Thanks


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## Suburban Jungle Life (Mar 1, 2018)

If you are adding 5 lbs of K to increase the bank, what about the K usage with N? If you use 4lb of N per year, should you add in an additional 2 lb of K so your total K for the year would be 7 lb/M? (N quantity for example. Not sure what your plans are.) I thought the average usage ratio of NPK was about 1-0.2-0.5? Thoughts?


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## g-man (Jun 15, 2017)

Yes that's the average numbers I use when you bag your clippings. If you mulch you are returning most of that. Re testing in the future will help understand how much is returning from mulching.


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## Ridgerunner (May 16, 2017)

That's an interesting problem and it's hard to say where to start in developing a logical progressive understanding.
The NPK ratio of 1:0.2;0.5 for plant turf usage is based on tissue (leaf/blade) analysis and does vary some for the different types of turf grown (See chart included somewhere in my tutorial thread.
Obviously, just because a plant takes up and uses nutrients in those ratios doesn't necessarily predict that those ratios will be determinant for soil application rates. For one, plant MGP (maximum growth potential) is going to be a controlling feature. In addition, there would be a number of other conditions that would affect nutrient usage and application rates: soil characteristics like soil texture and % OM; cultivation practices like aeration, de-thatching, clipping removal and mulching, irrigation, turf dormancy. chemical interactions within the soil where nutrients become so tightly bonded to be unavailable, etc, all of which can impact soil nutrient levels.
However, although mostly anecdotal at this time, superintendents that have employed the ratio method for nutrient application rates are reporting holding the soil bank (K) levels steady from year to year.
Personally, I question whether all of the factors previously listed would account for a consistent result in nutrient soil levels based on the 1:0.2;0.5 amendment/fertilization ratios.
One possibility that might produce a significant and consent impact on year to year soil nutrient levels is the cyclical loss of turf roots and corresponding affect of the nutrients held within roots. Studies have shown that annual root loss (for cool season grasses) of 33-50%+. Additional studies have reported that of this root loss, approximately 30% of the root mass in the top 10 cm (4") of soil is lost, and up to 90% of root mass at the 10 to 20 cm (4-8") level is lost. 
Regardless, whether the 1:0.2;0.5 application rate is accurate is unimportant (you have to start somewhere), If you can hold the soil bank nutrient levels reasonably consistent (say plus or minus 5-10% due to inherent inconsistencies in sampling and testing result) year to year, soil nutrient levels must be "optimal" as they are meeting the needs of the turf plant for that particular type of turf, soil and cultural practices.


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## Suburban Jungle Life (Mar 1, 2018)

@Ridgerunner Always got an answer! Love it! So, whether the plant does use that 1:0.2:.05 ratio or not, as long as a macro and perhaps some micros aren't at extremely low levels, it shouldn't be a limiting factor? Also, I guess if you have a really low CEC, then it may not matter how much you dump on it, it may all disappear in 6 months.


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## Ridgerunner (May 16, 2017)

@Suburban Jungle Life You nailed it. That's me, a little bit of knowledge and chock-full of opinion.



> ...as long as a macro and perhaps some micros aren't at extremely low levels, it shouldn't be a limiting factor?


I can't whole heartedly support that statement. Rather than "extremely low levels", PACE turf has developed minimum levels (The MLSN method) above which turf is described as "not performing poorly." Pretty subjective standard. Like the soil specialist from Nebraska, I support the theory of avoiding MLSN levels and using the more generous SLAN levels for the soil bank. That allows for more of a "buffer" and should insure that at no time during a growing season would soil levels drop below critical levels. (This isn't to discount the theory behind the MLSN method. Keeping soil bank levels low, you avoid possible nutrient deficiencies due to tie up of various nutrients due to chemical interactions and you allow for room to make "shock" applications of a specific nutrient that might be useful in counteracting a turf disease. Personally, I think it's too fine a line to walk when dealing with our home lawns. We have available alternatives to cure issues that arise that are not economically or practical in a large landscape/golf course setting. Besides our subjective appearance goals are commonly higher than their "not poor performing" standard.) The measure of the ratio feeding method is to maintain consistant nutrient levels from year to year and avoid any period of deficiency by keeping the target level well above minimums but safely below excessive. If that makes any sense.



> Also, I guess if you have a really low CEC, then it may not matter how much you dump on it, it may all disappear in 6 months.


Discounting the adverse effects that could occur by large applications of nutrients (e.g. P will chemical interact with micro-nutrients, tying up both P and the micro-nutrients, which are likely already scarce in a sandy, low CEC soil, making them less available for plant uptake), but, yes, quantities of cations in amounts in excess of CEC will leach. If it's a sandy textured soil, cations, and any other amendment, will leach relatively quickly. Spoon feeding can make up for that.
That begs another interesting question: Why is there a SLAN sufficiency level for sands and another for all other soils? How can a sand at nutrient levels almost halve the recommended nutrient levels of other (loam) soils be considered sufficient? Either turf needs X quantity of nutrients or it doesn't.
I opine this discrepancy may be due in large part to:
1. Studies that show that turf roots grow deeper in sandy soils than in loam or clay soils.
and
2. That studies show that roots proliferate in areas of the soil that contain concentrations of nutrients and moisture as reflected by similar increases in root mass in upper soil levels of turf that is watered frequently and "over" fertilized. 
JIMO, and I can't go without some rationalization for the questions that arise that I haven't yet found answers to. (<-- hanging participle)


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## Suburban Jungle Life (Mar 1, 2018)

@Ridgerunner Thanks again for taking the time to explain both data/facts and your reasoning. Much appreciated! :thumbup:


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