EFFECT OF SOIL PROPERTIES ON PHOSPHORUS SORPTION IN 13 SOILS WITH VARYING DEGREE OF WEATHERING

Phosphorus sorption by soils depends on a series of soil properties, most important of which are pH, clay, organic matter, cation exchange capacity (CEC), amorphous Fe, Al and Mn oxides, as well as CaCO₃. However, such properties may vary in soils of different degree of weathering. The aim of this work was to examine the soil properties that affect P sorption in 13 soils of Central Greece, evaluating the effect soil taxonomy may have on P sorption. We chose soils that differed considerably in pH (4 acidic and 9 alkaline) and in taxonomy (4 Alfisols, 4 Entisols, and 5 Inceptisols), and we conducted batch sorption tests with initial added element concentrations of C„=0-100 mg L^-1 at 1-to-10 soil-to-solution ratio. We measured sorption at C„=100 mg L^-1 (q₁₀₀) and the distribution coefficient, K_d-100 (equal to q/C at C₀=100 mg L^-1). We also measured important soil physico-chemical properties, and the sorption indices were correlated with the measured soil properties. When soils were divided according to taxonomy, we found that Alfisols had significantly higher CEC, amorphous Fe and Mn oxides, and q100, but also significantly lower P extractability (water soluble-P and Mehlich-3-P). The other two soil orders did not have different soil properties. When soils were divided according to pH, exchangeable Ca, and the two above mentioned P extractability indices were lower in the acidic group of soils than in the alkaline. These results suggest that although differences in exchangeable Ca are entirely pH-related, differences in extractable P, as well as CEC, Fe and Mn oxides and q100 are taxonomy-related. We also found that K_dl00.was significantly correlated only with exchangeable Ca (R²=0.304, p<0.05). Extractable P decreased with increasing sand, while organic C increased extractable P. We conclude that soil taxonomy is a key factor in understanding P sorption/extractability in soils, because highly weathered soils (here, Alfisols) have higher amorphous oxides content and this tends to enhance P retention by soils.

Extractable phosphorus, Alfisols, amorphous oxides

1. Al-Rohily, K.M., Ghoneim, A.M., Modaihsh, A.S., Mahjoub, M.O., 2013. Phosphorus availability in calcareous soil amended with chemical phosphorus fertilizer, cattle manure and sludge manure. Int. J. Soil Sci. 8, 17-24.

2. Arai, Y., Livi, K.J., 2013. Underassessed phosphorus fixation mechanisms in soil sand fraction. Geoderma 192, 422-429.

3. Fanning, D.S., Fanning, M.C.B., 1989. Soil Morphology, Genesis, and Classification. John Wiley and Sons, New York.

4. Igwe, C.A., Zarei, M., Stahr, K., 2010. Fe and Al oxides distribution in some Ultisols and Inceptisols of southeastern Nigeria in relation to soil total phosphorus. Environ. Earth Sci. 60, 1103-1111.

5. Naeem, A., Akhtar, M., Ahmad, W. 2013. Optimizing available phosphorus in calcareous soils fertilized with diammonium phosphate and phosphoric acid using Freundlich adsorption isotherm. Scientific World J. 2013, 680257 (article number).

6. Rowell, D.L., 1994. Soil Science: Methods and Applications. Prentice Hall, Harlow.