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Soil test shows high phosphorus

13 years ago

In need of some advise.
My soil test results from the lab
ph 7.3
no3-n 328
phosphorus 1173
potassium 2134
Apparently the phosphorus level is way too high. No commercial fertlizer has ever been added. The land had been bermuda pasture for the last twenty or so years. The soil we added is clay and compost 50/50.
The compost is horse manure, vegs, all as organic as known and composted to the right degree. The extentsion office states the nutrients are to the levels of posion. They state the ph,n,and potassium are adequate but the phosphorus is way too high. Has anyone lowered their phosphorus? This is a brand new raised bed garden so will this amount of phosphorus kill my vegetable plants?
Any advise will be greatly appreciated as I am a new gardener here in Oklahoma.
Jan

Comments (5)

  • 13 years ago

    It's extremely immobile in the soil. The immediate bad effects are less zinc and iron availability, but given that your pH is slightly alkaline applying zinc and iron to the soil probably won't help because it will be mostly unavailable.

    If you can lower your pH to 6.5-ish it might help. That said, your plants may be fine with the amount of zinc and iron available. When you plant look for signs of zinc deficiency (white/faded leaves) or iron deficiency (intervienal chlorosis) and apply a foliar spray if necessary.

    Eventually rain/water will drive a lot of the phosphorus out of the soil.

    Avoid manure amendments and all-purpose amendments for a while (years) and just apply N for fertilization.

  • 13 years ago

    Wow. I looked back at my own results from last year because my P was also high after years of adding compost. Mine was 208 and was classed as "very high." Your K is also quite high.

    Am I correct in assuming you just moved there and someone else owned the pasture for the last 20 years? If so they may have added too much phosphorus fertilizer to it. Hard to imagine that the compost you added would do that overnight.

    In any case, I don't have much more to offer. I wonder if there are crops that consume a lot of P that you could grow to help remove some? Animals need it for bones...I got it, plant chicken seeds! LOL

    I must be a little punchy. Did the extension office have any other advice besides just saying it was too high?

    I Googled "reducing high phosphorus in soil" and came up with the link below, and lots of others.

    Here is a link that might be useful: How to Correct High P - SF Gate

  • 13 years ago

    If I got a soil test reading that was super high, I think I would want to carefully gather another good representive soil sample from several depths and locations and send it to another lab that I thought would be reliable.

  • 13 years ago

    Thank you for the responses.
    Yes we just moved here and was told that the land was not used for the last twenty years so assumed it was not in the soil but in the the manure we added.
    The extension office just said I would not have to add fertlizer for many mnay years. I did call them and was told if I grew a cover crop in my beds this fall it would help to use up some of the phosphorus and use sulfur now to lower our ph and to just watch my plants and see what happens.
    I will take your advise and do another sample gathering very carefully and have it done elsewhere and compare the results.

    Thank you also for the article it sure explains things better. I have started 70 tomato varities plus lots of other vegs and sure hope they all do not die. We will wait and see and hope for the best.
    Thanks again for your responses.

  • 13 years ago

    I thought 'bermuda pasture' meant it had been used as pasture, i.e. for grazing, and therefore may have been fertilized. I see now your original post said it was never fertilized. In that case I would agree with another soil test.

    I assume you are getting a nice plug down to 6" (helps to use a bulb digger or a piece of pipe), from several locations and mixing them well. If for example you took the top inch and most of that was your compost, it would throw off the results.