Utilization of Soil Organic Phosphorus by Higher Plants

Utilization of Soil Organic Phosphorus by Higher Plants... 

Plants can absorb some soluble organic phosphates, such as phytin and nucleic acid that may be formed from organic matter, but such substances are so readily attacked by microorganisms that it is doubtful if direct absorption of these phosphates occurs to any appreciable extent in soils. Most of the phosphorus undoubtedly enters the root as the primary orthophosphate ion, H2P04, but a lesser amount may be absorbed as the secondary orthophosphate ion, HP04 . A low pH favors the uptake of the primary form and a higher pH favors the absorption of the secondary ion. Unlike nitrate, which is reduced when utilized by plants, phosphate remains in the oxidized state in organic combinations. 

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