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| it depends on the actual soil test used but in western region with alkaline soils the common test here in the US is the Olsens test. As mentioned by other posters, fertilizer P combines with other soil minerals so that the resulting compounds are not soluble with the extracting solutions used in the soil test labs. Here it takes about 9 # of P2O5 to raise the soil test by 1 # P. Note one is in the oxide equivalent which is how our fertilizer analysis is expressed but lab results are expressed as elemental P | |
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Soil Tests and Phos question
