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markmccarthy_gw

Excessive Phosphorus Levels

15 years ago

I started a small raised garden this year to grow summer squash and tomatoes. I bought the frame at Home Depot and had my lawn guy deliver a couple of yards of top soil.

The plants, which I grew from seeds, have not taken off. They are yellow in tone and stunted compared to other planted elsewhere in the ground.

I had the soil tested by Scotts:

pH is 7.50

Soluble Salt is 0.20

Phosphorus is 171.00 ppm (off the charts!!)

Potassium is 268.00 ppm (high)

Does anyone have advice for how to correct the Phosphorus imbalance?

Comments (13)

  • 15 years ago

    I think you are lacking nitrogen. Try some 10-10-10, maybe a teaspoon about 4 inches from each plant then water. Should see a difference in a day or two.

  • 15 years ago

    Mark:

    10-10-10 doesn't make sense when P is already too high. But madman may be right about the yellowing being due to nitrogen deficiency. There is no assurance that it is due to high P. I have seen higher soil tests with no apparent ill effects.

    P doesn't move much in the soil so leaching it out won't work. My only thought is to dilute with low P soil. But I'd try something else first, like adding N.

  • 15 years ago

    Try contacting your county agricultural extension -- New York State has a very good network. They can perform a more comprehensive set of tests and can make recommendations for correction.

    I don't know about the phosphorus level (or if it's likely to hurt your plants), but commercial "top soil" is often fairly poor in nutrients and organic matter. Your best bet might be to pull the plants out temporarily with as much of their soil ball as possible early on a cool, overcast day, and mix a good amount of bagged compost into the soil in your raised bed (say 1:4 compost to soil). Return your plants to the soil, water well, and shade them for a few days if possible.

    Meanwhile, how are the basics like watering, drainage, and sunlight? What's underneath the raised bed?

  • 15 years ago

    You might ask your lawn man just where he got the soil.

    And there is an article below that might give you some info.

    Sue

    Here is a link that might be useful: Phosphorus - Too much & plants may suffer

  • 15 years ago

    Notice that you are at the low end of the range which is described as 'giving problems for three to 5 years'. Still it is not clear what you have. If it is a nitrogen problem, all you can add, without adding P, is urea. Do not add 10-10-10 which will aggravate any P problems. If it is a problem due to P, you need iron-zinc foliar feeding. How do you distinguish between the two? The link below will give you an idea of the different deficiencies will manifest themselves.

    Here is a link that might be useful: ag.arizona.edu/pubs/garden/az1106.pdf

  • 15 years ago

    Two types of injury may occur: ( 1 ) An excess of one element may lead to a deficiency of another which ultimately results in a deranged metabolism, e.g., excess nitrogen or excess phosphorus may result in insufficient potassium and excess potassium may lead to deficiency of magnesium or calcium. This type of injury applies particularly to essential nutrients. ( 2 ) The presence of an element may directly injure the protoplasm and bring about the speedy death of the plant.

  • 15 years ago

    Excess phosphorous means nothing in a garden, no ill effects other then run off. Plants have a hard time absorbing phosphorous to begin with.

  • 15 years ago

    I've been gardening for a few years. I never did a "real" soil test until this year - always did garden store tests. I took my samples in early May and got results back a couple weeks ago. My phosphorus levels are a lot higher even than yours - 306 ppm. (ooops). My productivity was down a little last year, but it was a horrid year here in New England - very little rain. We do regular drip watering with a timer, but figured maybe that was it. Or the dratted oak trees that keep growing and stealing light. (Down to barely 8 hours for the veggie bed, I think.)

    I didn't see any unusual yellowing or anything of the sort last year, so maybe for whatever reason my plants didn't have a problem uptaking other nutrients. I guess my point is YMMV about this.

    My Cooperative Extension suggests not using manures or manure based compost for two years, then do another test. I hope to see the levels come down by then, but don't expect them to be fixed quite yet. This isn't something that can be corrected quickly.

    For you, it also sounds to me like a likely suspect is N deficiency. I also wonder about sunlight, water, drainage, etc. To build even better soil for the future, you might look into starting some compost. It will help not just with major and micronutrients, but beneficial fungi, etc, etc. Post some pictures and you'll get even better suggestions.

    Meanwhile, thanks for the great links, Belgianpup and Glib. I really enjoyed the articles. I printed them to help me keep an eye on things this summer.

  • 9 years ago

    Sorry to resurrect this discussion, but it seems like one of the better ones on the topic of excessive P. I also have this problem in a new school garden that the contractors brought in soil that has excessive P - anywhere from 50 to 125 ppm (there are 18 raised beds and I've tested most of them now). My soil test says optimal range is 4-14, and my highest bed of 125 is really not that high according to articles on this topic. However, our garden struggles to grow anything healthy except for a few species - mainly legumes. Curiously, one symptom that seems related in my garden is seedlings sprout without delay, but then go into a suspended state and never put out any true leaves. They don't die, but just stop growing at the seedling stage. Some species (i.e. carrots) if left long enough eventually will grow into mature plants, but take at least 3 times as long to mature.

    From what I've gathered, excessive P can be a problem in some gardens and not others, and that a problem may arise in certain vegetables and not others. My online research and discussions with my Coop Ext Master Gardeners have produced the following conclusion:

    1. It will take a few to many years to correct the problem as phosphorus is not very mobile or volatile in the soil. Overtime it converts to rock phosphate (unconfirmed source), or can run off into waterways and contribute to algae blooms.
    2. Do NOT add any more phosphorus in the form of fertilizers or manure-based compost (which is just about all commercial compost). If nitrogen is low use urea or blood meal or feather meal. Good NPK of common fertilizers.
    3. Might try adding carbon-rich mulch or compost, so long as it was not manure derived, to help "dilute" the excessive nutrient - but be aware that excessive carbon will temporarily bind up nitrogen as the carbon breaks down.
    4. Excessive P can cause other micronutrient deficiencies, particularly iron and zinc. In fact, this may be the only detrimental to plant health from excessive P. To address this, use a 0.5 - 1.0% iron zinc foliar spray up to once per week. Adding iron and zinc to the soil does not remedy the deficiency.
    5. pH of the soil is a factor that contributes to micronutrient deficiency. Good info on pH and P here. Also, any micronutrient that results in a positive ion (I, Ca, Zn, Cu, Mg, Mn, Al, etc.) interact with phosphorus in its conversion between available and unavailable forms. Here's a bit technical explanation on that. My soil is 7.0 to 7.5, so I'll need to factor that in when addressing my excessive P.
    6. Might try sampling soil differently, seeing P is not very mobile in the soil and often found in the top few inches of soil. If you dig below 6 inches to take samples, and compare to the samples taken near the surface, you might find that you could remove your top few inches of soil to correct the issue (probably only practical in raised beds).

    This is just the start of my intimate relationship with phosphorus. More to learn on this...

    Rusty

  • 9 years ago
    last modified: 9 years ago

    First, disregard the post about high levels of phosphorus being nothing to worry about. It can have a major impact on plant health, primarily by preventing the uptake of other, necessary plant nutrients. What many believe to be a N deficiency is rather excessive levels of P, as they can produce nearly identical symptoms. And excess P is a primary contributor to groundwater pollution, to the point where it is a restricted fertilizer in many states (most lawn ferts no longer include P).

    This fact sheet can help explain the issues with high P levels and how to fix.

  • 9 years ago

    Agree with gardengal48. Excessive P can be an issue - always to pollution potential to waterways, and often to plant health. I've read accounts of no issues to plant health with excessive P, but I personally am struggling with poor plant health. This leads me to believe that there are other factors in play, like pH and micronutrient levels, such that different gardens have different symptoms. For me, I first thought it was a low nitrogen issue as those plants that would grow had yellow leaves, and the only plants that grew well were my legumes, especially peas, as they fix their own N. But upon deeper investigation, my yellow leaves fit the description for iron deficiency with yellowing between the veins. Also, zinc deficiency presented itself as "drying" out of the leaves. I'm just now beginning treatment with iron/zinc foliar spray and will report back my results.

  • 9 years ago

    I wonder if growing phosphorus-loving veggies would help at all in reducing it. Or are excessive amounts leading to a form of P that cannot be taken up by plants?

  • 9 years ago

    Truth is that P is not really used that much by any vegetable......well nowhere as much as N or K. Problem is gardeners throw high P fertilisers thinking it encourages fruiting - and most native soils have adequate amounts of P to begin with.