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Soil Chemistry

Phosphorus Fractions and Release Patterns in Typical Mediterranean Soils

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

^* Corresponding author (adelgado{at}us.es)

Phosphorus forms dictate the P release potential of soils in agronomic and environmental terms. The main purposes of this work were to study P forms by sequential chemical fractionation in soils typical of Mediterranean areas, establishing correlations between P fractions and soil properties, and identify the relationships of specific P fractions to P release potential as determined using P sinks (anion-exchange resins). To this end, three different fractionation methods were used. A comparison of the results obtained with the three sequential fractionation schemes provides useful information about P forms in representative Mediterranean soils, allowing the distinction of P fractions which include: (i) the more labile P forms (essentially adsorbed P), (ii) most of pedogenic Ca phosphates, (iii) most of low soluble pedogenic Ca phosphates, (iv) lithogenic Ca phosphates, (v) P occluded in poorly crystalline Fe oxides, and (vi) P occluded in crystalline Fe oxides. The ratio of the P fraction, which includes the more labile P forms (essentially adsorbed) to combined non-organic P fractions was negatively correlated with soil pH (r = –0.83, P < 0.001) and positively correlated with the portion of combined Fe fractions related to poorly crystalline oxides (r = 0.84, P < 0.001). The greatest of P desorbable from resins (Q_max, in the Johnson–Mehl equation) was related mainly to the combined P fractions including adsorbed P and precipitated Ca phosphates in the studied soils. The amount of P desorbed at 1 h (Q_1h) accounted for a sizeable fraction of Q_max (between 29 and 59 %), the Q_1h/Q_max ratio being positively correlated with the portion of combined non-organic P fractions related to adsorbed P (r = 0.66; P < 0.01), and negatively correlated with the portion of combined P fractions related to low soluble pedogenic Ca phosphates (r = –0.67; P < 0.01).

Abbreviations: Cit, citrate • CA, citrate ascorbate • CB, citrate bicarbonate • CBD, citrate bicarbonate dithionite • EDTA, ethylene dinitrilo tetracetic acid • mG, Golterman fractionation method as modified by Díaz-Espejo et al. (1999) • OAc, acetate • OP, organic P • OS, Olsen and Sommers (1982) sequential fractionation method • R, Ruíz et al. (1997) fractionation method • TP, total P • WP, water-extractable P

This article has been cited by other articles:

				C. Saavedra, J. Velasco, P. Pajuelo, F. Perea, and A. Delgado Effects of Tillage on Phosphorus Release Potential in a Spanish Vertisol Soil Sci. Soc. Am. J., January 1, 2007; 71(1): 56 - 63. [Abstract] [Full Text] [PDF]