Premium
Factors affecting phosphate sorption along a Mediterranean, dolomitic soil and vegetation chronosequence
Author(s) -
CARREIRA J.A.,
LAJTHA K.
Publication year - 1997
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/j.1365-2389.1997.tb00193.x
Subject(s) - sorption , soil water , environmental chemistry , chemistry , chronosequence , carbonate , loam , adsorption , geology , soil science , organic chemistry
Summary Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi‐arid, mediterranean, dolomitic, soil and vegetation chrono‐sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse‐scrubland vegetation. These have small P sorption capacities, large Mg‐Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO 3 /HClO 4 digestion) concentrations (30–130 μg P g −1 ), of which up to 90% is Ca‐bound (HCl‐extractable), are typical of these young soils. P sorption markedly increased when Ca 2+ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra‐sorbed P is the labile‐P fraction sorbed on to (carbonate) surfaces and the apatite‐like fraction (NaHCO 3 ‐extractable and HCl‐extractable fractions). At the other extreme, older more‐intensively weathered, sandy‐clay‐loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P ( ca 400 μg P g −1 ), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl 2 was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe‐oxides (e.g. goethite and haematite) appear to be the most important P‐sorbing component for soils in the Mediterranean region, rather than amorphous Fe‐oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca 2+ , carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.