# Soil Report- Low Phosphorus



## YardWork314 (May 1, 2021)

I had a soil report done in the spring. Everything was pretty good besides nitrogen and phosphorus. I've been working on that, but I'm wondering how much phosphorus I should add before seeding this fall. The report level for phosphorus was a 4 which was labeled "low". They didn't include units, so I'm not exactly sure what 4 means (are soil reports standardized?). I already added one application of about 2lbs per 1000 based on a soil expert recommendation. My question is, would that be enough fix the problem? How often can you add higher application levels of phosphorus?


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## Zimmerman (May 20, 2019)

My last soil test came back as a 10 for phosphorus. My units were in lbs/acre. This was a University of Tennessee test. Not sure if your units would be the same. they have me putting down 2lbs of phosphorus per 1000 sq ft per year and retesting after 2 years. Not sure if you can do more than that or not.


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## Virginiagal (Apr 24, 2017)

Soil tests are not standardized. I have no idea what your test is or what a random unlabeled number means. Soil tests from reliable labs give recommendations for a whole year's worth of amendments. If you did not get that, then you should get another soil test.

Here are soil remediation guidelines:
https://thelawnforum.com/viewtopic.php?t=15165
Here is a thread on selecting a lab:
https://thelawnforum.com/viewtopic.php?t=7162
Most states have soil testing at the land grant universities in their state. Avoid the online companies like Soil,Savvy and MySoil.


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## YardWork314 (May 1, 2021)

It is actually a legitimate lab report. It just is kind of vague with regards to the units. It specifically has lbs per acre listed with potassium, but no units listed under phosphorus. I'm assuming (based on that and other info I read) that phosporus should be in lbs/acre as well.

I also had a weed identified that often invades areas with very low phosphorus. That's why I feel like I need to correct that as quickly as possible before overseeding.


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## YardWork314 (May 1, 2021)

Zimmerman said:


> My last soil test came back as a 10 for phosphorus. My units were in lbs/acre. This was a University of Tennessee test. Not sure if your units would be the same. they have me putting down 2lbs of phosphorus per 1000 sq ft per year and retesting after 2 years. Not sure if you can do more than that or not.


Thanks. I'm becoming more and more convinced that all nutrients on my report are likely in lbs/acre. For whatever reason, they just left that info off the phosphorus data.

Edit: It was definitely lbs/acre. Just received an email response from lab.


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## g-man (Jun 15, 2017)

What about posting an image of the report? Some use an index value that makes the math harder.


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## Virginiagal (Apr 24, 2017)

Here is what @Ridgerunner wrote in his soil test thread abiut maximum rates:

"Phosphorous
No more than 1-2#/M of P2O5 per application, not more than one application per 30 day period and not more than 4-6#/M total per season (best to apply higher rates after aeration to incorporate and reduce loss through erosion/run off). Do not apply if less than 30+ days prior to ground freeze."

As for how much you need, the lab should have given a recommendation for what you need over a year. Ask them if that was left out.


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## YardWork314 (May 1, 2021)

g-man said:


> What about posting an image of the report? Some use an index value that makes the math harder.


I received confirmation that it was lbs/acre.

I wanted to ask you specifically about this. You posted the following in the soil remediation guidelines



> If your phosphorus is low, then you can use:
> Triple superphosphate (TSP) 0-46-0 - Apply at 2lb/ksqft every month the soil is growing


4lbs per acre seems really low to me, so I assume I wouldn't run any risk of adding too much if I did another lighter application of TSP now and then I will also be using starter fertilizer before overseeding this fall. The starter will add about .8lbs of phosphorus per 1000.


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## YardWork314 (May 1, 2021)

Virginiagal said:


> Here is what @Ridgerunner wrote in his soil test thread abiut maximum rates:
> 
> "Phosphorous
> No more than 1-2#/M of P2O5 per application, not more than one application per 30 day period and not more than 4-6#/M total per season (best to apply higher rates after aeration to incorporate and reduce loss through erosion/run off). Do not apply if less than 30+ days prior to ground freeze."
> ...


Great, thanks. That was the info I was looking for.

The recommendation I got was 2lbs per 1000 once a year, but they said it might take a few years to correct. I was trying to see if I could speed that process up, since it is a problem area that will be re-seeded this fall. But, I also didn't want to over do it.


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## Ridgerunner (May 16, 2017)

> I was trying to see if I could speed that process up


There are a number of issues that can arise from "speeding up" from heavy applications of nutrients.

1. Run off. Unless you are plowing your lawn and incorporating amendments, you will be surface applying. Surface applied nutrients are subject to run off. Many nutrients (particularly phosphorous) are detrimental to the environment. If nothing else, it's a waste of money and effort if it runs off.

2. Heavy application creates an excess of that nutrient. This makes it harder for plants to access the other nutrients it needs and in some cases, plants will start substituting one nutrient for another that it uses for plant processes making those processes less efficient which can result in susceptibility to stress and disease.

3. Some nutrients (especially phosphorous) will form molecules with other nutrients, making both nutrients unavailable to the plant. Over application of phosphorous may create a deficiency of another nutrient like iron.

Turf only uses about 0.12 lbs/M of phosphorous for every pound of N used. If you apply 5lbs of N yearly, the turf will use only 0.6 lbs/M of P. Anything applied above the 0.6 lbs/M amount will build reserves and should increase future soil test values. 
Be conservative.


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## Virginiagal (Apr 24, 2017)

In Ridgerunners's third point, I think there is a typo and he means "unavailable" instead of "available."

The mycorrhizae decrease their activity in the presence of too much phosphorus. Don't want to discourage the mycorrhizae.


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## Ridgerunner (May 16, 2017)

Virginiagal said:


> In Ridgerunners's third point, I think there is a typo and he means "unavailable" instead of "available."
> 
> The mycorrhizae decrease their activity in the presence of too much phosphorus. Don't want to discourage the mycorrhizae.


 :thumbup: Edited, thanks!


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## YardWork314 (May 1, 2021)

Ridgerunner said:


> > I was trying to see if I could speed that process up
> 
> 
> There are a number of issues that can arise from "speeding up" from heavy applications of nutrients.
> ...


That makes sense. Thanks for the information.


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## 01Bullitt (Aug 31, 2020)

g-man said:


> What about posting an image of the report? Some use an index value that makes the math harder.


g-man, I found this chart on a website when I was researching a way to convert my P & K from a NC soil test index value to ppm. Can you confirm that it is the index number times the mg/dm3 column to get ppm?


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