DISTRIBUTION AND FRACTIONATION OF SOIL-PHOSPHORUS IN PARTICLE-SIZE SEPARATES IN SOILS OF WESTERN TURKEY

Evaluation of soil phosphorus (P) status is not possible without considering the various forms of P present and distribution of these forms in the soil fractions. Distribution of organic and total P on the whole soil and soil separates were examined in the selected three soil profiles representative to three great soil groups found in Izmir province in the Aegean region of Turkey. The results obtained indicated that total and organic P decrease, to a certain depth, as the depths of the soil profile increases. However, there is an increase in total P content in the lower parts of the B or in the upper parts of the C horizons in Profile I. In all the profiles other than Profile I, two-thirds or more of the total and organic P contents of the whole soil were concentrated in the clay plus silt fractions. The total P contents of the silt and sand fractions in Profile I were much more higher than the day fraction throughout the profile. In all the profiles, aluminum-(Al), iron-(Fe), and reductant-(Red) phosphate contents of the three fractions, namely clay, silt, and sand, were highest in the surface and subsurface horizons, but tends to decrease at the expense of calcium (Ca)-P as the depths of the profiles increase.