Organic soil phosphorus is plant-available but is neglected by routine soil-testing methods

In top soils of arable land the percentage of organic phosphorus (P) can range from 20 to 80% of total P concentration. The objectives of our studies were to investigate the effects of an addition of organic P (Na-hexaphytate, C6H6O24P6Na12) on the P bioavailability of various plants (maize, phacelia, pigeon pea, rape, sugar beet, wheat, white lupine) in a standardized soil experiment. Therefore the effect of organic P on growth and P uptake of various plants listed was compared to those fertilized with Ca(H2PO4)2 or without a P addition and the effect of organic P addition on extractable soil-P was analyzed with routine soil-testing methods. Application of organic P (Na-hexaphytate, C6H6O24P6Na12) to a soil did not result in a significant increase of extractable soil-P measured by routine soil-testing methods (CAL, DL, NaHCO3, EUF, Me-III, Water) although the applied organic P was available for various plant species: maize, phacelia, pigeon pea, rape, sugar beet, wheat, white lupine. The results indicate that the bioavailability of organic soil-P is not taken into account by routine soil-testin