N-P-K Ratios...

Discussion in 'Soils, Fertilizers and Composting' started by kia796, Feb 23, 2007.

  1. kia796

    kia796 Active Member

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    I've always been puzzled as to whether there's some "basic knowledge" I should have when buying fertilizer (other than taking Chemistry), over and above that they mean Nitrogen, Phosphorus and Potassium.

    I know N produces green growth, P is important for root and flower development, and K for winter hardiness. And that "numbers" invariably include fillers. But ratiohas been mentioned in these forums several times.

    Evergreen fertilizer, for example. I've seen 8-6-8, yet others (and I've thrown empties away) also said evergreen yet their formulations didn't maintain the ratio, (i.e. 16-12-16, or 4-3-4).

    Guess what I'm asking is: what is the optimum ratio for, say, the evergreen family? Is there some general standardized knowledge for ratios...without going back to school?
     
    Last edited: Feb 23, 2007
  2. JanetW

    JanetW Active Member

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    Evergreen fertilizer 30-10-10, I use Plant Prod. Usually you can decifer which is best for the given situation from the packaging, it usually states what the particular ratio is best used for. Janet
     
  3. kia796

    kia796 Active Member

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    Thanks, JanetW. It's not that I don't trust fertilizer producers, it's simply that somewhere in these forums (I think it was millet?), suggested that fertilizer strengths don't really matter (among what's available), as long as the ratio is the same.

    So, 8-6-8 (which I've used for evergreens...a Scott's product I think), has a different ratio than 30-10-10, which you use.

    I've read, for example, cultural instructions for Wollemia nobilis that suggested 6-0-6 (no phosphorus). Is it then correct to believe a 12-0-12, or a 3-0-3--which follow the ratio issue--is also recommended?

    Are ratios only an indicator of optimum formulations?
    A chemistry/horticulture class is probably what I need. I just can't get my head around this.
     
  4. Ron B

    Ron B Paragon of Plants 10 Years

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    30% N sounds like something that would be intended for lawns. On many (most?) soils probably the bulk of such a high dose will not be used and will run off to end up in the aquatic system.

    Soils are best sampled and sent out for analysis before fertilizing. In this region (Vancouver to Portland) many sites may only benefit from N supplementation, applications of P and K may be superfluous. Repeated applications can produce a toxicity, this is known to be a problem with P in particular.
     
  5. biggam

    biggam Active Member

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    There are various aspects to this question, but I bet you will learn what you want from this thread. A major question is what is the fert. being applied to? If it is going into potting soil (which starts with little fertility) then general suggestions for certain crops can be followed. If you are fertilizing something in the ground (in native soil of what? fertility characteristics) then a general suggestion (or product) may not be the best thing to do (though it may be okay). Often the native soil provides adequate nutrients for plants in the landscape; if you want to effectively (and efficiently) apply fertilizer, then a soil test may be advisable -- an agricultural university or private testing lab could do this. Phosphorous tends to bind to the upper soil layer, so it's not much use adding for deep-rooted plants, and it may be present in high amounts on land previously farmed. Nitrogen is generally the prime nutrient limiting maximum growth, however, maximum growth may not be your goal. Potassium is water-soluble (like nitrogen) and is often needed where nitrogen is needed (again, this is getting general). The last "tree, shrub, & evergreen" fertilizer I bought was 9-6-6, and I bought it specifically for the ratio of nitrogen to potassium. To get at the initial question, a 3-1-2 fert. compared to a 9-3-6 fert. is the same ratio, so you would need 3 lbs. of the former to provide 0.09 lb. of N, or 1 lb. of the latter to provide the same amount of N. Make sense?
     
  6. kia796

    kia796 Active Member

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    thanks, biggam, I'm getting there...

    I bought it specifically for the ratio of nitrogen to potassium.

    How did you know that was the ratio (N to K) that you needed?

    I look at my soil test results, remembering that young evergreens don't do well here until they're older. And wonder how these numbers translate into knowing which evergreens fertilizer, of the many that are available, to use.

    Test results:
    CEC 6.6
    soil pH 7.9
    Buffer pH ---
    Soluble Salts 0.14
    Exchangeable Calcium (Ca) 1229
    Exchangeable Magnesium (Mg) 35
    Exchangeable Sodium (Na) 8
    % H Base Saturation 0.0
    % K Base Saturation 1.8
    % Mg Base Saturation 4.4
    % Ca Base Saturation 93.3
    % Na Base Saturation 0.5

    Available Phosphorous (P) 14
    Exchangeable Potassium (K) 46
    Available Zinc (Zn) 0.4
    Available Manganese (Mn) 3.5
    Available Copper (Cu) 0.6
    Available Iron (Fe) 11.0

    Though the soil test was done for, say, apple trees (and recommendations were specific to apple trees so I've omitted them), HOW to YOU look at those numbers and KNOW what type of fertilizer to buy to provide optimum conditions for evergreens?

    I don't want to spend the money to do another soil test (and tell the agency) to recommend for evergreens, rather than apples.

    At the risk of insulting horticulture professionals, is there a rule, or code, or fundamental fertilizer knowledge that can help me make the right choice of the many evergreen fertilizer formulations available?

    I know that evergreens tend to like a lower pH, so for years now, I've fertilized young evergreens with a small amount of 21-0-0 (knowing that the sulphur in ammonia sulphate will help lower the pH). They respond by throwing more annual growth than those I didn't fertilize, yet still not to the degree I've witnessed on young evergreens at other properties.

    I won't be insulted if you say "go back to chemistry class".
     
  7. biggam

    biggam Active Member

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    An extension website recommended a ratio of 1.25 to 1 (N to K2O) for fertilizing apples, and I bought it with that in mind, trying to get close to that ratio.

    Ammonia sources of N have an acidifying reaction in the soil, while Nitrate is a slightly basic reaction, and Urea is slightly acidic in its final reaction. I'll let someone else tackle the rest of your latest post :)
     
  8. kia796

    kia796 Active Member

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    Thanks for your explanation.

    Found the following (technical) report, in which fertilizing of spruce was tested:

    Nitrogen accumulation or luxury consumption can occur in nature during pulses of N availability or when supply exceeds the capacity of plants to utilize N for growth...N is invested in storage...New nursery cultural techniques, such as nutrient loading...were designed specifically to stimulate this natural phenomenon, where fertilizer is supplied in excess of demands for current growth to induce luxury uptake.
    Optimum N loading occurs at maximum plant N uptake without causing growth decline, usually achieved at the transition point between luxury consumption and excess fertilizer addition....The newly validated model shows promise as a tool for quantifying fertilizer indices for other species or cultural systems, as well as improving diagnostic precision of tree seedling nutrition.


    The title is "Optimizing Nitrogen Loading of Picea mariana seedlings during nursery culture. Authors: K.F. Salifu and V.R. Timmer.

    Interesting reading, despite its technical stuff. Deficiency to toxicity was covered too.

    High N fertilizers allow the conifer to store N for later use.
    So I'll stop questioning the "optimum ratio" issue! :)
     
  9. kia796

    kia796 Active Member

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    Yippppeeeee, found it...and then this thread can retire!

    http://ohioline.osu.edu/hyg-fact/1000/1002.html

    excerpt:
    Woody plants respond well to fertilizers with a 4-1-2, 3-1-2, 4-1-1, or 3-1-1 ratio such as 24-6-12, 18-6-12, 20-5-5, 12-4-4, respectively. Landscape plants respond to 3 to 4 times as much nitrogen as phosphorus, and twice as much potassium as phosphorus. An application of three pounds of actual nitrogen per 1,000 square feet using a 3-1-2 ratio would include one pound of P2O5 and two pounds of K2O.


    Thanks for your patience with my questions...
     
  10. growest

    growest Active Member 10 Years

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    Kia--one other thing I notice is your very wide ratio between Ca:Mg. Tho you can't remove calcium you could certainly try bumping up the Mg a bit...some agronomists like to see about a 7:1 ratio, yours is more like 20:1
     
  11. kia796

    kia796 Active Member

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    Would frequent and liberal applications of Epsom Salts do the job? Cheap and easy to apply.

    Would bumping up the Mg also have the benefit of lowering the pH (albeit only a little). Tad high for evergreens, isn't it? Or did I throw things off by, over the years, sticking mostly with 21-0-0 (in addition to several years of 8-6-8)?

    I felt on our property there was something "out of whack" (hence the thread) because young evergreens don't do well here until they're about 10 or so. Thanks growest!
     
  12. growest

    growest Active Member 10 Years

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    Kia--I'm personally nervous about trying to change anything really quickly...I would tend to apply lots of small doses of the epsom salts. As you say, cheap and effective. I suspect you'll see some nice results very quickly with this.

    The Mg will probably tend to raise the pH even more, but it's already so high it won't make things noticeably worse.

    As a rule, trying to raise pH is way easier than lowering it. My feeling is that the only practical, long term way to drop pH is biologically...I would apply a bit of compost wherever possible as often as possible. Soil microbes tend to push pH toward the ideal range over the long haul.
     
  13. kia796

    kia796 Active Member

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    Oops of course Mg raises pH! We've used literally tons of sulphur (can't remember if it was elemental or flowers of sulphur?), some had to be scratched into the first two inches of soil (destructive in turf areas). Had hoped the 21-0-0 would've done more by now.

    We've been "at this" for nearly 30 years, and the pH has dropped .3 !!
    I agree with you that biological is ALWAYS the best way, but supply is the problem.
    Thanks for the discussion, growest.
     
  14. growest

    growest Active Member 10 Years

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    Wow, 30 years! Looking at the calcium reserves your soil must have, it will take centuries to try to neutralize it all with added sulphur.

    Unfortunately, all that sulphur is also hard on the microbes that help evergreen roots survive in less than ideal conditions (sulphur is a pretty good fungicide).

    Mulches might be useful, I agree trying to get and apply compost is a lot of expense and work. Chips from tree companies are one usually free source of mulch, and quite light to work with. What sort of "evergreens" are you growing?
     
  15. kia796

    kia796 Active Member

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    it will take centuries to try to neutralize it all with added sulphur.
    Time to give up amending...!

    all that sulphur is also hard on the microbes a gardening Catch 22.

    We had brought in several truckloads of bark mulch from a sawmill, which cost us only the shipping. Supply now is no longer free, as the sawmill has installed a cogeneration facility. Bark waste is now used to generate electricity. Good for the environment, bad for mulch-purchasers.

    Years ago we had planted an apple orchard, with one adjacent acre planted to 600 D.fir as a cut-your-own Christmas tree operation. While the apples thrived, the Christmas trees (where we learned by trial-and-error that sulphur-based 21-0-0 fertilizer allowed the trees to thrive) were hit by Tussock Moth in, I believe, the sixth year. But by then we had gained most of the stand's anticipated economic return.

    The south-slope, semi-arid North Okanagan site wasn't conducive to large scale D.fir but at 8foot x 8foot spacing, it did work for a few years. We're now retired, and have cut down the orchard too (well-seasoned apple firewood is fabulous).

    But my love for conifers remains a passion, which are now grown only for our enjoyment: Mugo pines, Spruce (not really suitable here because of the heat and winds but I was able to get them cheap), and D.fir (which really "take off" after about 10 years of TLC).

    As stated earlier, young evergreens don't grow well, despite copious irrigating. Of all the ground covers tried (textile covered in rock; turf; textile covered with bark mulch; bark mulch alone), bark mulch does yield the best results, but tends to blow onto grassy areas during frequent high winds.

    We're definitely in pine country, but a Forestry Dept. "seed tree" map included a D.fir in a canyon 100 feet from my property line.

    A few pics (showing chlorosis?): The first five photos show trees 6 years old, with bone meal added into the planting hole...I wish I had known about miccorhizae (sp?) before! The last photo shows a Pine about 20 years of age.
     

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