I have the wrong formula there. Ppm is the same as lb/acre at 3 inches (ppm = 3/3 lb/ac). Ppm x 2 = lb/ac at 6 inches (or ppm = 3/6 lb/ac). At 4 inches, ppm = 3/4 lb/ac. At 5 inches, ppm = 3/5 lb/ac. Ppm stays the same. lb/ac increase as you go deeper (more dirt included for each additional inch of depth).

This is really interesting, I was just looking for a good tool to differentiate between ppm, lbs/acre, and #/1000 ft2.

Becky,

I use the following:

ppm x2 multiplied by whatever depth I want determined as the numerator with 6 as the denominator.

For 6" depth: ppm X2 X 6/6

For 5" depth: ppm X2 X5/6

For 4" depth: ppm X2 X4/6

etc

It's easy for my itty bitty mind to remember.

Good way to remember that!

For anyone reading along, when you report your depth as a certain number of inches, the lab will report its findings either as ppm or lb/ac and if it's lb/ac, it's lb/ac for the number of inches you reported. If you had reported 3 inches instead of 4, you will get entirely different numbers for lb/ac. Ppm is the same no matter what number of inches you report.

Ridgerunner - Per your method above, it looks like 6" of depth is the baseline for which PPM is calculated. Is this assumption correct? (Ratio of 1)

It would appear that most fertilizer recommendations are for 3" of depth?

Meaning:

Ideal PPM 18-33 for N2.

33 = Ideal Max PPM for N2.

33 x 2 x (3/6) = 33 #/acre or 0.76 #/1000fts.

OR? Is my assumption of 33 being the ideal PPM for N2 wrong? At 22 ppm, i get 1#/1000 @ 6", which would make sense too.

Ridgerunner - Per your method above, it
looks like 6" of depth is the baseline for which PPM is calculated. Is
this assumption correct? (Ratio of 1)

No, ppm is nothing more than parts of one thing found in a million units of something else (a ratio so to speak). In the case of soil analysis, it is not necessarily related in any way to soil depth. The assumption (ideally) is that the the distribution is consistent throughout every inch of soil.

It would appear that most fertilizer recommendations are for 3" of depth?

That would depend on what the recommendation is for. For agriculture it is for an acre furrow slice (often tons of a nutrient per acre to a depth of 6.7". For a garden, it is usually made in pounds per 100 sq ft. to a depth of 6 or 6.7". For a residential yard it is usually made in pounds per thousand square feet to a depth of 4". Depends on the lab and the analyst.

Meaning:

Ideal PPM 18-33 for N2.

33 = Ideal Max PPM for N2.

33 x 2 x (3/6) = 33 #/acre or 0.76 #/1000fts.

OR? Is my assumption of 33 being the ideal PPM for N2 wrong? At 22 ppm, i get 1#/1000 @ 6", which would make sense too.

You lost me. N2? Nitrogen gas? Most labs measure NO3 or NO3 and NH4.

I don't bother with N content of the soil, it's very volatile, highly dependent on weather/climate/season and can change considerably within a day. I can't give you the optimum ppm of the top of my head, but 1#/k monthly has proved sufficient for lawns. I can say NO3:NH4 ratios may be important to grass health in some cases, but that study is in its infancy.

Becky,

"it's lb/ac for the number of inches you reported."

Are you sure on that? For the reported values or the recommendations?

Reported values.

Thanks Becky.

You are totally correct as far as LL reports their findings. I've never seen that anywhere else, but then I've always used ppm values.

That explains a few issues that I have had with Logan Labs test reports. Now I'm outright disgusted with them.

It's extremely embarrassing that I didn't catch that on my own and way before now.

It would appear that I have some recommendations to review and numbers to crunch. Good thing I usually am somewhat conservative.

I don't understand the problem. Their extractant would give a ppm and then, for the customer, they convert it to lb/ac. They would use the reported inches to make the conversion. How else would they do it? If you're talking about what they report as a shortage, that's the lb/ac deficit to make the base cations come into their "ideal" balance. It's not a recommendation.

The consensus recommended values (that are based on years of field testing by universities, agronomists and soils scientists) for determining soil deficiencies, sufficiencies, optimals and excesses are published as ppm (not pounds per area-that's to be calculated by the user). Most every soil lab that I have experience with reports tested values in ppm, the few that give lbs/acre base it on a acre furrow slice. LL is the only lab that I have run across that reports base cations and P (P2O5) only in lbs/acre adjusted for depth of sample. In spite of numerous warning signs, I ignorantly assumed they were reporting for acre furrow slice, a 6.7" depth (yes, yes people commonly round down to 6 for ease of calculation). So to do my recommendations, I was dividing their reported lbs/acre values by 2 to get ppm.

THAT's the problem.

If I wanted to make the process of soil analysis and recommendations as complicated, convoluted and mysterious as possible, I couldn't pick a better lab than Logan. }:<

Sorry about my tone, I've had a long night reviewing recs.

Call Logan Labs to make sure how they do it. I'm going by what I was told by someone else. Also, if they were reporting lb/ac at the 6 inch furrow slice depth, it wouldn't matter what the reported depth of the sample was. I think they do adjust for reported depth of the sample.

I'm certain that they adjust for depth. I did the math and verified it. The only one I'm not sure of is P, but I assume that that is also adjusted to depth, it would only be logical. I am not going to call LL, if I ever do another LL besides the one's I'm currently involved in, I'll use an adjusted P value, just to be safe.

Thanks again Becky for the eye-opener.

Ridgerunner: My apologizes for writing N2 as Nitrogen. With my work and dealing with Nitrogen gas everyday, it's just a shorthand method I use when typing - poor on my part.

Kudos to you as well, most folks wouldn't go back and edit their recommendations for random strangers. Your attention to detail and passion for the subject shines! Hats off...

Skip,

Thank you.

I'm sorry if you were left thinking I was being dismissive and giving short shrift.

So, No need to apologize. You threw me, that's all, but a valid inquiry. N2 is relevant to plant health and NO3 availability, but in a detrimental way. Anaerobic microbes will reduce the soil NO3 presence through the denitrification process when certain soil conditions exist. This results in the release of N2 to the atmosphere as the microbes use the oxygen from the NO3 for life processes in oxygen depleted environments. Not a good thing, but valid when discussing plant and soil health.

On the 6" baseline issue. As I mentioned ppm isn't dependent/calculated based on depth, but acre slice furrow weight quantities are. For instance, if your report states that your soil has 10 ppm of potassium, or 10 units out of every 1 million units is potassium, then in one million pounds of soil, there will be 10 pounds of potassium. As the standard is an acre slice furrow and an acre slice furrow weighs 2 million pounds (one acre of soil 6" in depth - 6.7" to be "exact"), an acre slice furrow with 10ppm of potassium, will contain 20 pounds of potassium.

ppm X 2 = lbs of "whatever" per acre (acre slice furrow).