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Confused about when to fertilize

Discussion in 'Fertilizer Application' started by Victorsaur, Jun 21, 2013.

  1. Smallaxe

    Smallaxe LawnSite Fanatic
    Messages: 10,082

    If you want to reduce those 'algae blooms' in the 10,000 lakes, then start cleaning out the leaves, sticks and trees from the water... thelittle P that washes into the lakes probably equals the little P from the wildlife... around here we have open water spring-fed lakes filling up with enough organic material to fertilize corn fields for at least one season,,, but dnr says leave it in there... why do you suppose that is??? :)
  2. turfmd101

    turfmd101 LawnSite Bronze Member
    Messages: 1,375

    Posted via Mobile Device
  3. phasthound

    phasthound LawnSite Fanatic
    Messages: 5,138

  4. Skipster

    Skipster LawnSite Bronze Member
    Messages: 1,084

    Phasthound gave a great link for understanding soil test P (and laying the foundation for understanding soil tests for other nutrients). I've been raked over the coals on this board (by the usual suspects) for saying what is in this very passage (paragraph 2 of phastound's link):

    "The soil P tests that are used today provide an indication of the level of soil P that is available to the plant. The tests do not determine the total concentration of P in the soil or even the actual concentration of available P, but provide an index measurement of the P that can be taken up by the plant."

    You will never extract all the P from the soil complex without destroying the sample, but the total amount of P doesn't matter. The total amount of plant-available P doesn't even matter. The important part of soil testing is correlation-calibration -- knowing how plant responses correlate to different test values and knowing how fertilizer application rates influence soil test nutrient levels.

    For example, the only reason we know if soil test values are high or low is that we've tested soils with plants that have exhibited deficiency symptoms and we've tested soils with plants that looked really healthy. The only reason we know how much fert is required to bring a soil back to the optimal range is that we've fertilized different rates on soils with particular soil test values and monitored nutrient levels and plant response after that.

    Soil tests aren't the end-all-be-all of plant nutrition. But, they give us a darn good idea of where we are and how to get where we want to be.
  5. Smallaxe

    Smallaxe LawnSite Fanatic
    Messages: 10,082

    Thanks for the link...
    it sounds as though they have the capability to measure how much P is in a given soil, but chose to report only the relevant amount that is expected to be plant available...

    Annual crops have very little chance of acquiring AMFungi in their root systems in order to mine the unavailable P in the same way that lawns are able to do, so their concept of High/Low P in the testing process is skewed from that angle right off the bat...
    i.e. what may be Low for corn, will be more than adequate for turf,,, and this article appeared to consider corn and soybeans...

    IMO,,, turf managers would be further ahead in promoting the soil health and beneficial Fungi than dumping on ferts that are recommended for 240 bushels/A of corn... I still say that grass is the easiest thing in the world to grow, in that it does so well b4 we start meddling to make it better... :)
  6. Skipster

    Skipster LawnSite Bronze Member
    Messages: 1,084

    I think you're still a bit confused (maybe because we didn't explain it well enough). The point of a soil test is to estimate how much of a particular nutrient is available for plant uptake from the soil and correlate that to plant responses in order to gauge fertilizer needs. Mycorrhizae have very little to do with this.

    Also, optimal soil test ranges and fertilizer recomendations are done for specific crops -- there's not a "one size fits all" system like you're talking about. Check out this "Understanding the numbers on your soil test report" paper from the University of Arkansas (http://www.uaex.edu/Other_Areas/publications/PDF/FSA-2118.pdf). Pay special attention to the "Nutrient Availability Index" section and the 'Phosphorus (P) and Potassium (K)' paragraph. You'll see there that optimum soil test levels are different for different plants. For example, little yield response is seen in row crops and forages when fertilizer is added and Mehlich III soil test-P exceeds 36 ppm, but vegetable crops will benefit form fertilizer applications until Mehlich III soil test-P reached 75 ppm.

    Because turfgrass is not grown for grain or biomass harvest, yield is not a factor used in corelation/calibration studies. Instead, color and growth are often used to determine when a fertilizer response occurs in turf crops. Optimum levels and recommendations are not designed to drive corn production, but are designed to produce green healthy turf.

    You need to understand what the soil test report means before you can use it.
  7. phasthound

    phasthound LawnSite Fanatic
    Messages: 5,138

    That is not necessarily true, there are studies that show an increase in yield with crops that have been inoculated with mycorrhizae.
  8. Smallaxe

    Smallaxe LawnSite Fanatic
    Messages: 10,082

    I realize that innoculation of AMF does create the exception to the rule,,, but that is getting ahead of ourselves in the point that was being made about turf vs. annual crops...

    I appreciate that people believe that plant available P in their soil test reports is the only important numbers that matter,, but my point is that turf has the ability to utilize P beyond the "available P"...

    Whereas uninnoculated annual crops are not likely to have time to build the symbiosis with AMF and 'mine' the unavailable P,,, the soil testonly needs to address the available P for agriculture... the reason I was curious about whether soil test would address ALL phos. in the soil is becuz turf grass potentially accesses ALL phos. in the soil...

    This moves into new territory regarding the usefullness of ag. based soil test, so plz don't re-explain the current usage of soil test numbers... I'm challenging the concept of P being low for turfgrass just becuz the available P doesn't seem to be high enough for the lab technician running the test...
    If I am missing something then perhaps I could be informed as to what EXACTLY I am missing,,, and perhaps it could be done in a manner of intelligent discourse ... :)
  9. Skipster

    Skipster LawnSite Bronze Member
    Messages: 1,084

    The research does not support your opinion here. Several papers published in the journal Plant Physiology report that AMF does not increase the amount of P taken up beyond "available P", but instead expands the surface area from which "available P" can be extracted. AMF don't "mine" more P than roots do -- they just increase the area from which P can be found. They also report that AMF are ubiquitous in the soil and naturally form associations with more than 80% of all plants, Poaceae included.

    Research has found that most crops for this association on their own within hours after germination

    Nothing can access ALL P in the soil. Remember, the soil test in only an index value. It's not a concrete number.

    EXACTLY what you're missing is the very meaning of a soil test. It's not a concrete number and it has nothing to do with what a lab technician thinks. The test values and recommendations are backed up with decades of field research -- stuff that was actually done on lawns and research plots.

    All the soil test does is find a way to assign a measurable value to a soil sample, correlate that value to plant activity, then calibrate fertilizer applications to the soil test value and to plant activity.

    The absolute value of any soil nutrient is unneeded.
  10. turfmd101

    turfmd101 LawnSite Bronze Member
    Messages: 1,375

    I have had conversations with Lee Bloomcamp on studies showing applying Milorganite two times per year will help P go from unavailable to available in the soil, "slowly". If anyone is unaware of who Lee Bloomcamp is, you may be industry illiterate. Just saying.

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