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Old 07-13-2013, 02:44 AM
Victorsaur Victorsaur is offline
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Join Date: Feb 2011
Location: Asheville, NC
Posts: 78
Great to see this thread turning into a good discussion. An article written by NCSU (NC State) states that :

Phosphorus and calcium move very slowly through the soil profile so to be most effective they should be incorporated into the top 6 to 10 inches. These elements can be surface applied but the nutrients will not be as readily available to the plants and will be less effective. It is impossible to tell how much calcium and phosphorus are required without a soil test. However, because most North Carolina soils are low in phosphorus, it is usually safe to add 1 to 2 lbs of P505 per 1000 sq. feet. For soil incorporation of phosphorus, triple superphosphate (0-46-0) is recommended. For 1 to 2 lbs of P505, incorporate 2 to 4 lbs of triple superphosphate per 1000 fe of bed area. Diammonium phosphate (18-46-0 or 16-48-0) is the most soluble phosphorus source and should be used if phosphorus is applied to the surface. For 1 to 2 lbs P205, apply 2 to 4 lbs ofdiammonium phosphate per 1000 ft2 of bed area. This will also supply 0.4 to 0.8 lbs of nitrogen per 1000 sq. feet.

So the argument remains that what this article states is innacurate given that there is already a lot of P available in the soil? Perhaps it varies from soil to soil? The "Tree Doctor" who has been working for huge businesses like the Biltmore estate also says that soils around here are so naturally devoid of Phosphorous that they can usually be amended with a granular application, particularly DAP, but it can take some years to take an effect on the soil.
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