Questions about organic sources of phosphorus

appletree729April 3, 2014

My soil tests indicate that I need to increase phosphorus levels. The recommendation I received with the soil test was to add 1.0 lb per 100 sq ft of 0-46-0.

I know that bone meal and rock phosphate are both sources but the calcium reading on the test was also really high, so I'm concerned about adding more calcium via bone meal (does rock phosphate have a lot of calcium as well? Any drawbacks to rock phosphate?)

If I use rock phosphate, I'm unsure of the rate at which I should be applying it - I was going to order off amazon and there are no instructions in the description.

Any tips would be greatly appreciated!

Also - What do people use to raise just the phosphorus levels on lawn? Can I use rock phosphate here as well? Or would you need massive amounts - we have a large lawn and I don't want to be deadlining with several hundred pounds of fertilizer.


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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Link below is to a very informative previous discussion here of this question. It contains a number of sources you can use.

My primary suggestion would well composted manures as well as non-manured compost. Composted manure will supply all the P most any situation requires for both the lawn and the garden. Well dried, it can be applied to lawn areas with the average fertilizer spreader too.


Here is a link that might be useful: Organic sources of phos

    Bookmark   April 3, 2014 at 11:13AM
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The first soil test I had done here said the levels of Phosphorus and Potash were "low optimum" and the amount of organic matter was barely measureable. After a few years of adding enough organic mater, compost and other forms of vegetative waste, the soil tests showed that P and K levels had moved to "high optimum" levels, No other source of P was used other than the organic matter.
I have seen that quite often, soils low in organic matter also testing low in other nutrients that are turned around simply by adding adequate amounts of organic matter.
Any source of Phosphorus you add to your soil will require an active Soil Food Web which requires a soil with adequate levels of organic matter in the soil to function and provide that to the plants growing in that soil.

    Bookmark   April 4, 2014 at 6:26AM
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Thanks - a couple of issues though with adding more organic matter/compost - first, the areas that I am referring to compromise two large areas of our property - the first, the lawn, which is very large - about 9000 sq feet in total. In the past, I've tried to find a way to spread compost over that large of an area and it's just not going to happen, lol.

The other area is not as big and I could easily add compost for nutrients, but I don't think the organic matter is a problem - it's almost 17% here! Which I think is really high! And the lawn itself has 7% OM which I think is also good.

I wonder if compost tea would be a good alternative? Adding microbes and nutrients without the weight (or necessity) of adding compost for organic matter?

Does anyone use guano to raise their phosphorus levels? I wonder if that would be a quicker way to correct the imbalance and then I could maintain it with compost tea?

    Bookmark   April 4, 2014 at 7:29AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

There is some discussion about the guano use in the thread I linked above. My problem with using it is the cost of it when compared to the cost of bagged composted manures - cost difference is night and day. Not to mention the odor difference! :)

I make my own composted manures but bagged is available at something like $2 a 2 cf bag around here.

But I've got to say that IMO 17% org matter sure isn't sufficient and obviously 7% isn't either. I always shoot for 25-30% minimum and more is better.

As for problems spreading compost over a large area - that all depends on the quality of the compost. That can range from coarse mixes of unfinished particles to humic liquids.

While tow-behind special equipment is available for spreading even the coarse stuff it isn't necessary (check local equip rentals). You can easily spread fine textured compost with the average push fertilizer spreader.


    Bookmark   April 4, 2014 at 11:27AM
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As for your original question, calcium phosphates supply roughly twice as many calcium ions as phosphorous ones (for what that's worth) but the other materials in rock phosphates are unknown. In the southwest, much of those are dolomite and other limestones.

As for spreading landscaper-quality topping materials on grass, the rule of thumb is one cubic yard covers 1000 feet 1/3 inch deep, so 9000 feet one inch deep requires 27 yards of stuff, very very roughly $800 from a recycling landfill/dump.

    Bookmark   April 4, 2014 at 5:12PM
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art_1(10 CA)

NPK is by weight so if the recommendation is 1.0 lb per 100 sq ft of 0-46-0, then you could use ~20 lbs per 100 sq ft of 5-2.5-6 horse manure or 46 lbs per 100 sq ft of 1-1-1 compost. These organic sources may vary so this is an estimate.

You can try rock phosphate e.g. ~15 lbs per 100 sq ft of 0-3-0 etc. I am not sure if high calcium in soil is too big of a deal, or about organically fertilizing the lawn. Some say to use alfalfa or soy meal.

    Bookmark   April 6, 2014 at 10:44PM
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I'm surprised the recommendation was for so much P, what they suggest amounts to an equivalent of 200 lb/A P2O5 = 87 lb/A P (check my math :) ).

    Bookmark   April 13, 2014 at 5:56PM
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