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Coastal Plain Soils of Southeastern Nigeria: II. Forms of Extractable Iron, Aluminum, and Phosphorus
Author(s) -
Lekwa G.,
Whiteside E. P.
Publication year - 1986
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1986.03615995005000010030x
Subject(s) - udic moisture regime , ammonium oxalate , loam , soil water , chemistry , mineralogy , dithionite , entisol , oxalate , geology , soil science , inorganic chemistry , biochemistry , enzyme
The distribution of citrate dithionite and ammonium‐oxalate extractable Fe 2 O 3 and Al 2 O 3 were determined in nine Coastal Plain pedons of southeastern Nigeria. Distribution of available, organic, and active inorganic forms of P, plus the P fixation and available water holding capacities of these soils were also studied. The dithionite extractable Fe 2 O 3 and Al 2 O 3 generally increased with depth and clay contents in each of the six, loamy, well drained pedons studied. The active Fe ratio usually decreased with depth, suggesting that higher proportions of Fe 2 O 3 were generally present in more crystalline forms in the lower horizons of the well drained soils. The active Al ratio usually increased with depth, but it was high throughout in the more poorly drained, loamy aquic pedons. The well drained ustic pedons contained larger amounts of Fe 2 O 3 ‐d than did the well drained udic pedons. They also contained more Fe 2 O 3 ‐d than Al 2 O 3 ‐d, and the active Fe ratios were higher (≧ 3). The loamy udic pedons and the loamy aquic pedons contained larger amounts of Al 2 O 3 ‐d than Fe 2 O 3 ‐d, particularly in the latter. The sandy Aquod was very low in dithionite and oxalate Fe 2 O 3 and Al 2 O 3 , except that the spodic horizon had maxima of dithionite and oxalate Fe 2 O 3 . Available and total active P contents of the studied soils were generally low. The relative abundance of the extractable inorganic P forms was generally in the order of Fe‐P > Al‐P > Ca‐P in the well‐drained loamy pedons. Organic P in all the pedons was relatively high in the surface horizons and constitutes the most abundant form of P measured in these soils. Phosphorus fixation increased with depth and showed close positive correlations with free iron oxide and clay contents.