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Phosphorus Fractions and Release Patterns in Typical Mediterranean Soils

Departamento de Ciencias Agroforestales, EUITA, Universidad de Sevilla, Ctra. Utrera Km 1, 41013 Sevilla, Spain

View larger version (22K): [in a new window]   Fig. 1. (a) Relationship between the combined inorganic P fractions according to Golterman as modified by Díaz-Espejo et al. (1999) and the combined P fractions according to the other two fractionation methods used: Olsen and Sommers (1982), and Ruíz et al. (1997). (b) Relationship between the sum of extracted P in the first three steps in the fractionation method of Ruíz et al. (1997) and the sum of extracted P in the first two step in the modified Golterman fractionation method (Díaz-Espejo et al., 1999).

View larger version (20K): [in a new window]   Fig. 2. Olsen P (Olsen et al., 1954) and water-extractable P (WP) as related to P extracted by Ca-EDTA + dithionite (Ca-EDTA-P, Golterman as modified by Díaz-Espejo et al., 1999).

View larger version (16K): [in a new window]   Fig. 3. (a) Citrate bicarbonate dithionite P (CBD-P) as related to the amount of Fe extracted in the same fractionation step (CBD-Fe) (Ruíz et al., 1997). (b) The P/Fe mole ratio in CA extracts as related to the ratio CA-Fe/combined Fe fractions.

View larger version (14K): [in a new window]   Fig. 4. (a) Relationship between the ratio of P extracted by CA-EDTA + dithionite (Ca-EDTA-P) to the combined of P fractions (Díaz-Espejo et al., 1999) and soil pH. (b) Relationship between the ratio of P extracted by citrate (Cit-P) to the combined P fractions (Ruíz et al., 1997) and soil pH.

View larger version (15K): [in a new window]   Fig. 5. (a) Ratio of P extracted by resins at 1 h (Q1h) to the maximum extractable P (Qmax in the Johnson–Mehl equation) as related to the ratio of P extracted by CA-EDTA + dithionite (Ca-EDTA-P) to the combined of P fractions (Díaz-Espejo et al., 1999) and to (b) the ratio of P extracted by citrate (Cit-P) to the combined P fractions (Ruíz et al., 1997).