soil test shows crazy high P level

This is my first year growing, raised several plants organically outdoors in the ground. Results were terrific.

I started from seed in nursery pots then transplanted to the ground in June. Based on results of a soil test last spring, I dug 3' diameter holes about 1 foot deep and backfilled with composted cow manure mixed at about a 4:1 ratio with native soil plus a few amendments.

Decided to test the amended soil this fall to help guide me for next spring. Phosphorus was off the chart--in the original native soil it was 14.3 lb/A, but the amended soil report says 3,433 lb/A! That's a 240x increase. Recommended level is 20-40. I know cow manure has phosphorus in it, but that much? I made compost tea out of the cow manure regularly (maybe 2-3 times per month) and I topdressed with some fishbone meal twice last year (a few weeks before flower and then about halfway through flower) but it wasn't a massive amount--roughly 1 cup per plant?

Sounds like too much phosphorus can lock out iron and zinc. But elsewhere I read not to worry about it, just don't add any more for several years and eventually it'll get used up.

Opinions? Anything backed up with data would be especially helpful, but I'll take your general knowledge and experience too.

My original thought was to plant in those same spots again and they won't need much feeding except some nitrogen during veg. But now I'm wondering if I should plant elsewhere and learn a lesson here.

Also noticed that my pH was a bit high: 7.3 (native soil is 4.9). Best way to lower that a bit?

Here's the report I just got:


And the original report from last spring:

Here's a link to one article that says too much P leads to micronutrient lockout.

But I've read other things that say no big deal.

Thoughts?

NewEnglandFarmer said:

Here's a link to one article that says too much P leads to micronutrient lockout.

But I've read other things that say no big deal.

Thoughts?

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Useful tips they give there. You could always dilute the soil by mixing normal soil and amend with a high nitrogen like a high-nitrogen guano. Since your ph is high could play around with peat a bit.

It appears you've done well in the micro nutes,most other tests are quite low from what people have posted.

Had an email exchange with the guy who runs the soil test lab here. He didn't seem too concerned about the P levels.

I suppose maybe if it was a problem I would've had issues this past summer.

But will definitely add something to lower the pH down below 7.

You think I should do this now or wait until spring? Seedlings won't go in until June.

NewEnglandFarmer said:

Had an email exchange with the guy who runs the soil test lab here. He didn't seem too concerned about the P levels.

I suppose maybe if it was a problem I would've had issues this past summer.

But will definitely add something to lower the pH down below 7.

You think I should do this now or wait until spring? Seedlings won't go in until June.

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May as well wait. Yea peat is gonna lower that nicely for you.

NewEnglandFarmer said:

Had an email exchange with the guy who runs the soil test lab here. He didn't seem too concerned about the P levels.

I suppose maybe if it was a problem I would've had issues this past summer.

But will definitely add something to lower the pH down below 7.

You think I should do this now or wait until spring? Seedlings won't go in until June.

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You are in trouble if you are relying on folks on here, 99% of people on here don't even test their soil. I just hired a soil agronomist($40) and the price of Logan Labs Mehlich 3/Saturated past test. If you just have a Mehlich 3 test and no Saturated paste(solubility) test, then you really don't know where your P #'s are really. Mehlich 3 test alone, they want you to GUESS and suggest that 90% of P is locked up in the soil and that might be why they tell you not to worry about it. However, if this is a solubility test like the Saturated paste, then you should worry... OK, it looks like you have the Mehlich 3 and Modified Morgan's test. I'm not familiar with Morgan's testing and it could be a solubility test or just tested at different Ph? Yeah, I looked it up and Morgan's is a weak acid and Mehlich 3 is a strong acid extraction method. I don't think that either one is a solubility test like a saturated paste. @Northwood get in here and help this man with his "Local extension test". This seemed to be your preferred testing method, drop the mic for us!!!

Oh sure, go wind me up with worry after I was all set to chill out on this potential issue.

Joke--glad you chimed in. Had no idea about test methodology.

I'm still unsure about this, but here's another piece of anecdotal data: pretty sure a number of decent growers on RIU (including the remarkable @ganga gurl420) use a very heavy hand with the composted cow manure. With fantastic results. Their P levels must be sky high too.

Which leads me to think there are other factors involved in determining whether high P does any harm. pH maybe? Or level of other nutrients? I'm not a soil scientist so am groping in the dark here. The guy at the lab seems knowledgeable but from my Google research there doesn't seem to be 100% consensus on this topic.

Be great to get @Northwood's opinion on the matter.

NewEnglandFarmer said:

Be great to get @Northwood's opinion on the matter.

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I say just go with your original plan: add no more amendments that introduce phosphorus and you should be okay. Just be aware that if your soil is subject to leaching and have a natural water body you or others care about nearby, it may cause issues there. This is the biggest danger of excessive phosphorus. I'd avoid inputs of compost (use a wood chip mulch instead), and for N apply blood meal or something like that.

Just get your pH to a good level if possible. Edit: Don't go overboard with your pH correction. Maine gets a good amount of precipitation, so it might lower a bit naturally in time as well.

These tests measure "extractable" and "soluble" phosphorus, meaning recommendations for inputs if any correspond to the length of the growing season in your area. This makes sense, considering unless you're testing your nutrient strength in your hydro reservoir, you need to know the amount of nutrients you need to get through more than a single day. Keep in mind that phosphorus is an anion, but combines with aluminum or iron in your soil to act as a cation getting a weak positive charge. Thus part of the available pool will be directly related to your CEC as well.

Northwood said:

I say just go with your original plan: add no more amendments that introduce phosphorus and you should be okay. Just be aware that if your soil is subject to leaching and have a natural water body you or others care about nearby, it may cause issues there.

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Understood. There's a brook not too far away, but we're talking about a pretty small area of soil--six 3-foot diameter planting holes. Plus lots of thick vegetation between the garden and brook to act as a buffer zone for any runoff. Although maybe you're talking about leaching below the surface? In any case I don't think the actual total sum amount of P is very large.

Northwood said:

I'd avoid inputs of compost (use a wood chip mulch instead), and for N apply blood meal or something like that.

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I've read about blood meal attracting critters who will dig up the dirt and destroy the root zone. But maybe I can find another good N source that doesn't have any P. Or maybe the risk of critters is small.

Northwood said:

Just get your pH to a good level if possible. Edit: Don't go overboard with your pH correction. Maine gets a good amount of precipitation, so it might lower a bit naturally in time as well.

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The report has a recommended amount of sulfur to add--I'll just have to do a little math to reduce it for the actual planting areas. You think I should do that as soon as the frost is out of the ground to give it time before the plants go in?

Northwood said:

Keep in mind that phosphorus is an anion, but combines with aluminum or iron in your soil to act as a cation getting a weak positive charge. Thus part of the available pool will be directly related to your CEC as well.

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Thanks, professor. What is CEC? Sounds like I have some studying to do if I'm going to understand soil chemistry/biology.

NewEnglandFarmer said:

Sounds like I have some studying to do if I'm going to understand soil chemistry/biology.

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That goes for everything

NewEnglandFarmer said:

Thanks, professor. What is CEC? Sounds like I have some studying to do if I'm going to understand soil chemistry/biology.

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It's a measure of how well your soil can retain certain nutrients without them washing out of your soil. Nutrients will "stick" to microscopic sites on soil particles, and even flushing 100 times in a row will not get rid of them. This forms a reservoir of nutrients that your plants can draw upon over the growing season. It's like money in the bank

It's on your soil test above labeled "CEC" and your value after amendments is 21.6 which is excellent for outdoor regular soil.

It's extremely important to farmers because with low CEC their fertilizer application will not be fully held by soil and organic matter particles and wash out to the ground table or nearby water sources. Based on their CEC figure, they will split their recommended nutrient dose into a two or more applications over the growing season to avoid that problem. Fertilizer is expensive.

NewEnglandFarmer said:

The report has a recommended amount of sulfur to add--I'll just have to do a little math to reduce it for the actual planting areas. You think I should do that as soon as the frost is out of the ground to give it time before the plants go in?

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Yeah I'd do that, but after most of the early spring rains are over (if your weather is anything like your neighboring Nova Scotia). It does take time for sulfur to react to form acids in soil, so earlier is better. You could just kinda evenly top dress it, and let the rain take it in. Elemental sulfur is cheap, so you have that going for you. Weird that you'd have issues of high pH in Maine though after so many decades of high SO2 pollution with ample precipitation, so I'd do the math then divide by 2 to start off with half the recommended application this year. I could be wrong though since I've never lived in Maine, but damn close! lol

Edit: I wouldn't worry about the blood meal. Mix it in a bit with the top couple inches of soil, and by the time your plants are larger it will be composted and gone. Don't put it at the root zone. Bacteria will release nitrogen from it, and fungi and water movement from rain or watering will bring it down to where it's needed. Plus mulch with wood chips or something as I mentioned on the very top to keep everything moist and happy. Just worry about rabbits and critters like that eating your plants on the top!

Northwood said:

Weird that you'd have issues of high pH in Maine though after so many decades of high SO2 pollution with ample precipitation, so I'd do the math then divide by 2 to start off with half the recommended application this year. I could be wrong though since I've never lived in Maine, but damn close! lol

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The native soil test came in at 4.9--I added a little lime when I mixed the composted manure with the native soil, because the native soil was so acidic, but I may have overshot the target a bit.

Northwood said:

Edit: I wouldn't worry about the blood meal. Mix it in a bit with the top couple inches of soil, and by the time your plants are larger it will be composted and gone. Don't put it at the root zone. Bacteria will release nitrogen from it, and fungi and water movement from rain or watering will bring it down to where it's needed.

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Should I add it in May, several weeks before I transplant the seedlings? Then if any critter did decide to dig around, wouldn't be a big deal. Plus that would give the soil microbes time to break it down and make the N available.

Northwood said:

Plus mulch with wood chips or something as I mentioned on the very top to keep everything moist and happy. Just worry about rabbits and critters like that eating your plants on the top!

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Last summer I used hay for mulch, which seemed to work well. Could try woodchips too this year.

Last year only critter issue was a chipmunk that dug a hole in the root zone of one of the plants--fortunately I discovered it early and was able to trap and relocate the little bugger.

Actually, there was one other issue. While applying compost tea one day a soaked mouse popped out of the mulch and scurried away. When I investigated I found a little burrow with babies in the root zone. They were all soaked from the tea but still alive. I moved them to a spot underneath some brush where I'd seen the mama go, but not sure if they survived. Felt kind of bad but not much I could do.

@NewEnglandFarmer Yeah you can add blood meal in May after the earlier spring rains are mostly over. Funny story about blood meal: I've read long ago that it was a repellant to animals that might eat your crop rather than an attractant. Many years ago I was in the second year of a newly planted 1/2 acre orchard and the deer were driving me crazy. These trees were all grafted dwarf apple trees of several varieties, and rather expensive. So I spent several hundred dollars on many bags of blood meal, and spread it all around the orchard border, mostly in the direction from the woodlot where the deer walked from each night. It was like the deer never even noticed it. Noise makers and wind activated movement worked much better. Lol

You might consider using wheat straw as an alternative to hay. Hay is both a mulch and amendment due to it's much higher nutrient content, especially nitrogen. It's like 0.6% phosphorus too, while straw is like 0.1% if memory serves me right. It's why hay is used as animal feed while straw is used for bedding. Straw is also much cheaper than hay.

Sorry to hear about the baby mice. Little rodents are a critical part of the food chain that sustain a lot of other diversity. Once I cut down a tree, and a nest of baby flying squirrels fell out of it without the parent(s) in sight. We took them home and the kids tried to feed them milk from an eye-dropper but they all ended up dying one-by-one over a few weeks

NewEnglandFarmer said:

Thanks, professor.

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Careful, this is a forum. If he was that good, he would be charging people for his advice. That's why I suggested hiring an agronomist for $40. My EXP with taking advice on RIU is that I'll get led down a dark alley and get fucked. EVERYBODY on this forum needs help and it's not really a good place to get critical information. People will sound smart enough, but they will fuck you in the end... Most agronomist will use Logan Labs or Spectrum Analytic and will get both a Mehlich 3 and Saturated Paste test. I got a Mehlich 3, Saturated Paste, water test, and reccomendations for $110. I hired the agronomist and he filled out the paper work for me so that I wouldn't have issues with ordering test(yes it's complicated). I was ordering these tests on my own in past and I later realized that I wasn't asking for a "Weighted Scoop" for my indoor soil, so my test results were skewed. This isn't a problem with ground soil, but I'm just putting it out there.