Phosphorus

Discussion in 'Organic Lawn Care' started by Smallaxe, Jun 25, 2009.

  1. Smallaxe

    Smallaxe LawnSite Fanatic
    Posts: 10,080

    Does anyone have any ideas about P being water soluable? This was reviewed rather considerably during a discussion of 'Stinky Lake Sydrome' a couple of years ago.

    The general findings were that P binds to the soils quickly and will never move, into the Lakes. That view has just been challenged and was wondering how it works.

    Please NO list of reading materials, unless there is a snippit to source a point. The real question is:

    What is the 'exception' to the rule that causes the P to leach and how does that happen?
     
  2. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    HUH? Did you miss my "list"?
     
  3. JDUtah

    JDUtah LawnSite Silver Member
    from UT
    Posts: 2,636

  4. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

  5. drugrep

    drugrep LawnSite Member
    Posts: 44

    Binds with Calcium in high pH, and Aluminum and Iron in low pH.

    My understanding is that it's better for it to bind with Ca than with Al or Fe.

    P does move slowly. Once you have desired PPM obtained, you don't need to use it that much. Some will get lost through plant uptake and I imagine molecules will dissociate into neighbors yards, but that would be slow.

    You've heard me say a dozen times that I am very low on P. I live across the street from a retention pond, but my soil needs P and I'm adding it.

    I think it's possible if you already have high P you can have P run off. Crusting, compacted, clay soil may not absorb rain water and P fertilizer eroded into drains. I think that's where the biggest problem is. Once I get my PPM to 50, I'll switch to P free fertilizer and only apply when I drop to 40. I want a minimum of 40 ppm.
     
    Last edited: Jun 25, 2009
  6. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    Why 50? 50 would be considered a very high or excessive level for most all turf grasses and testing methodologies. What testing method is being used and/or do you have a test available to look at?
     
  7. drugrep

    drugrep LawnSite Member
    Posts: 44

    Olsen method since my pH is high. I see recommendations split. Some say 25 is enough, some say 40 is enough. I'm going with higher since us Americans think bigger is better! <grin>. I will say once I reach 25, I'll stop using starter fertilizer year round. I'll quit obsessing about it when I reach 25 ppm.
     
  8. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    General phosphorus recommendation for optimum growth using the Olsen P method is 10 mg P/kg (10 ppm). This number can fluctuate somewhat depending on the soils P sorption capacity and other P related chemistry, however I think you are still overdoing it shooting for 25.

    Long story short, it is difficult to nail down a number without a better knowledge of the soils chemistry, which is something a standard soil test will not reveal. So I would shoot for a value between 10-15 mg P/kg for starters if you are using Olsen P method for testing.

    Another way to monitor your P (myco associations aside) is to find your most P sensitive plant in the landscape, when a deficiency shows up do a leaf tissue test and soil test . Alternatively, if all you are concerned about is your turf with regard to P, then monitor the turfs leaf tissue.
     
  9. drugrep

    drugrep LawnSite Member
    Posts: 44

    Kiril, there is not a thing wrong with my grass, but because most of what I read said it should be 25-40, I am obsessed with the thought that my roots aren't all they can be.

    I had 2 tests by 2 different labs, numbers were close and my P average between the 2 is 14 ppm.

    I am consumed with getting it to 25. I have put starter fert down 3 times already this year. I am going to stop for the summer, but my grass growing so fast, I can't believe my shoots aren't thinner from all the N and rapid growth. They are actually in great shape though.

    I am obsesses, and I can't stop until that P gets to 25.

    Now a positive note, I do think all that P is helping my grass spread. It is getting denser. Maybe a combo of all the P & N, but I've got it in my mind that my roots are getting better from the P and why my shoots aren't too thin from overuse of N.

    If I could find a inexpensive source of P only, I'd use it, I'm not trying to get all the N, it's the P in the starter I'm after and I really am obsessed with this.

    I joked in another thread about bugging the soil guys at the university I attend. I wasn't joking though, they seem to love talking to me about all of this, but I feel bad because I have spent so much time over there.

    The positive of all the fertilizer and rapid growth though also helps lower my pH which is 7.6

    I have silt loam soil with CEC I think was around 18. Mg very high at around 750 ppm, Ca around 3500 ppm. K very high at 350 ppm. Organic matter low was around 3%, but that can take decades to build to 5-6%
     
    Last edited: Jun 25, 2009
  10. Kiril

    Kiril LawnSite Fanatic
    Posts: 18,298

    Too much P can lead to other problems. In the process of your quest to 25 you just may make it worse.

    There are far more important factors to root growth than soil P levels, like soil moisture, structure, temperature, etc... You say your turf is fine (i.e. no visible signs of P deficiency), so unless you can actually quantify a direct benefit from continued P applications, I would recommend you stop applying.
     

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