RELATIVE EFFICIENCY OF FE-OXIDE STRIP FOR EXTRACTING PHOSPHORUS IN SOME EGYPTIAN SOILS

Three methods for extracting available phosphorous in some Egyptian soils, has been compared with Fe-strip method which proposed by Tzy-Huei Lin et al. (1991). Moreover, to provide a base of comparison, a biological treatment was also established. The results showed that the highest total-P value was recorded for clay soils (1943 mg kg’1), followed by calcareous soil (848.55 mg kg1) and sandy soils (627.4 mg kg1). Amongst the tested soil properties, the statistical analysis revealed that only clay content (r= 0.696 ) and calcium carbonate content (r -0.601j were significantly correlated with the total-P, The data showed that the extracted P percent (from its total) by the tested extractants may be ranked as follows; Soltanpour and Schwab (5.56%) > Fe-strip (13%). While Brayl and Olsen and Sommers methods released minor portion of P. the high P portion extracted by Soltanpour and Schwab may be due to 1) a particular affinity between DTPA and P, 2) this extractant may released various pools of P beside the available portion into solution and 3) the effect of high ionic strength (1M) of NH4HCO. The data also showed that the percent of P released from calcareous soils > sandy soils > clay soils. This may be attributed to the employed methods that may destroy a number of P-minerals in calcareous soils, consequently the recovery % of P increased. While the minor percent of P released from clay soil may be attributed to its highly adsorptive power in that soil. The statistical results showed that Fe-strip was significantly correlated with the widely used soil extractants (r= 0.451 j. The results of biological evaluation of the tested methods indicated that only Fe-strip (M4) ad Olsen and Sommer method (Ma) were significantly correlated with the amount of P-uptake by plants. The regression equations for this relation were: Y 12.29 + 0.94 X R2 = 19.9 Y = 15.30 + 4.86 X R2 = 19,6, respectively. These results concluded that Fe—strip method was satisfactory and gave reliable information about available P for plat.